[EE]: OpAmp Max differential input voltage GL358

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[EE]: OpAmp Max differential input voltage GL358

Justin Richards
Experimenting with using a ESP8266 as a soldering iron PID controller
driving the ADC with the output of an opamp.

The GL358 opamp datasheet specifies max differential input voltage as 32V.

I would like to know if that is as it sounds and I can force the inputs to
have a max of 32v across them with a single supply to the Opamp of +5V.  I
am still learning about opamps and thought the inputs were to be considered
as a virtual ground and they will effectively be at the same potential but
here i would be brute forcing a voltage across them and concerned it may be
damaging and bad practice.

The GL358 (was in the junk box) is configured as a dual amp to amplify the
thermocouple (integral part of soldering tip) output of approx 2mV - 8mV
(~30oC - 400oC)  .to approx 40mV - 1500mV.

One side of the thermocouple is grounded and connected via a resistor to
the inverting input while the other side is connected via another
resistor to the non-inverting input.

I plan to measure temperature then apply 24V across the thermocouple. which
will drive 24V across the two 1k ohm opamp input resistors.

As a caution I plan to have back to back diodes at the inputs to limit the
voltage across them to approx 0.7v.

But back to the original question, are the protection diodes needed given a
maximum differential voltage of 32 volts or is that only if the supply is
also at 32V.

I found a design that disconnects the thermocouple from the opamp during
heating but not sure if that is actually required and obviously simplifies
the design if not.

Regards
Justin
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Re: [EE]: OpAmp Max differential input voltage GL358

Clint Jay
I think perhaps you've got a few misconceptions here.

Thermocouple usually refers to a dissimilar metal junction sensor, applying
heat to it creates a voltage across the two wire ends*, you don't feed
power to a thermocouple.

Most chip datasheets specify the maximum input voltage in relation to VCC,
your GL358 (if I'm reading the datasheet right) will be able to cope with
VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V, 32V will
probably release the magic smoke.

*Thermocouples are *really* useful, put enough of them in series and apply
fire, you can charge a car battery!!!

http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g



On Sat, 12 Sep 2020 at 10:00, Justin Richards <[hidden email]>
wrote:

> Experimenting with using a ESP8266 as a soldering iron PID controller
> driving the ADC with the output of an opamp.
>
> The GL358 opamp datasheet specifies max differential input voltage as 32V.
>
> I would like to know if that is as it sounds and I can force the inputs to
> have a max of 32v across them with a single supply to the Opamp of +5V.  I
> am still learning about opamps and thought the inputs were to be considered
> as a virtual ground and they will effectively be at the same potential but
> here i would be brute forcing a voltage across them and concerned it may be
> damaging and bad practice.
>
> The GL358 (was in the junk box) is configured as a dual amp to amplify the
> thermocouple (integral part of soldering tip) output of approx 2mV - 8mV
> (~30oC - 400oC)  .to approx 40mV - 1500mV.
>
> One side of the thermocouple is grounded and connected via a resistor to
> the inverting input while the other side is connected via another
> resistor to the non-inverting input.
>
> I plan to measure temperature then apply 24V across the thermocouple. which
> will drive 24V across the two 1k ohm opamp input resistors.
>
> As a caution I plan to have back to back diodes at the inputs to limit the
> voltage across them to approx 0.7v.
>
> But back to the original question, are the protection diodes needed given a
> maximum differential voltage of 32 volts or is that only if the supply is
> also at 32V.
>
> I found a design that disconnects the thermocouple from the opamp during
> heating but not sure if that is actually required and obviously simplifies
> the design if not.
>
> Regards
> Justin
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


--
Clint. M0UAW IO83

*No trees were harmed in the sending of this mail. However, a large number
of electrons were greatly inconvenienced.*
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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
Hi Clint,

yes, thermocouples are as you say but with the T12 style soldering tips the
thermocouple is also used as the heating element as strange as that
sounds.  There are only 2 connections to the tip and it provides both
heating and temperature measurement.

I am testing on my bench and applying 12v getting it hot then connecting to
the op-amp and reading the output and has survived many cycles.  And
convinced its a thermocouple as reversing the connections to the op amp has
the expected outcome.  I am so tempted to connect the 12v while connected
to the opamp  ( I found a spare) as it is protected by the 2 x 1k ohm input
resistors but I will heed your advice.

This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed engineered the
same station I have.  On closer inspection I don't see the disconnect when
heating.  I was sure that schematic had a disconnect transistor to protect
the opamp, I will have to watch again.

That station is ok, except I want a web page to tweak all the PID constants
and a rotary encoder with OLED display for fast temperature adjustment.  It
currently has a weird insert card and clunky non-intuitive buttons for temp
adjust.

All is tested ok, my code supports MAX6675, DHT, thermistors and 4diodes in
series and is used at home to make black garlic where the humidity is
maintained with a peristaltic pump etc among other things

A very early version can be seen here
https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller

I now want to leverage of all that development and control a soldering iron
the way I want it.  Fast heating, setable standby temp, easy adjust, just
need to do the last bit.

Cheers Justin

On Sat, Sep 12, 2020 at 5:29 PM Clint Jay <[hidden email]> wrote:

> I think perhaps you've got a few misconceptions here.
>
> Thermocouple usually refers to a dissimilar metal junction sensor, applying
> heat to it creates a voltage across the two wire ends*, you don't feed
> power to a thermocouple.
>
> Most chip datasheets specify the maximum input voltage in relation to VCC,
> your GL358 (if I'm reading the datasheet right) will be able to cope with
> VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V, 32V will
> probably release the magic smoke.
>
> *Thermocouples are *really* useful, put enough of them in series and apply
> fire, you can charge a car battery!!!
>
>
> http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
>
>
>
> On Sat, 12 Sep 2020 at 10:00, Justin Richards <[hidden email]>
> wrote:
>
> > Experimenting with using a ESP8266 as a soldering iron PID controller
> > driving the ADC with the output of an opamp.
> >
> > The GL358 opamp datasheet specifies max differential input voltage as
> 32V.
> >
> > I would like to know if that is as it sounds and I can force the inputs
> to
> > have a max of 32v across them with a single supply to the Opamp of +5V.
> I
> > am still learning about opamps and thought the inputs were to be
> considered
> > as a virtual ground and they will effectively be at the same potential
> but
> > here i would be brute forcing a voltage across them and concerned it may
> be
> > damaging and bad practice.
> >
> > The GL358 (was in the junk box) is configured as a dual amp to amplify
> the
> > thermocouple (integral part of soldering tip) output of approx 2mV - 8mV
> > (~30oC - 400oC)  .to approx 40mV - 1500mV.
> >
> > One side of the thermocouple is grounded and connected via a resistor to
> > the inverting input while the other side is connected via another
> > resistor to the non-inverting input.
> >
> > I plan to measure temperature then apply 24V across the thermocouple.
> which
> > will drive 24V across the two 1k ohm opamp input resistors.
> >
> > As a caution I plan to have back to back diodes at the inputs to limit
> the
> > voltage across them to approx 0.7v.
> >
> > But back to the original question, are the protection diodes needed
> given a
> > maximum differential voltage of 32 volts or is that only if the supply is
> > also at 32V.
> >
> > I found a design that disconnects the thermocouple from the opamp during
> > heating but not sure if that is actually required and obviously
> simplifies
> > the design if not.
> >
> > Regards
> > Justin
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> Clint. M0UAW IO83
>
> *No trees were harmed in the sending of this mail. However, a large number
> of electrons were greatly inconvenienced.*
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
In reply to this post by Clint Jay
>
>
>
> http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g


That made for an interesting read, some clever designs. I did not know
RTG's used heat this way.
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards
A thermistor is not a thermocouple.  You could never put a thermocouple across the heating element, thermocouples have very low resistance, it would pop like a fuse if you put voltage on it, they are normally connected to a very high resistance.  Thermocouples produce mV of output, the op amp you want to use has a high input offset and high input offset drift, it would completely obscure the the actual input voltage.

I think that station monitors the resistance of the element, after briefly disconnecting it from the power supply. Something like this <https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/>


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 5:12 AM, Justin Richards <[hidden email]> wrote:

> Hi Clint,
>
> yes, thermocouples are as you say but with the T12 style soldering tips the
> thermocouple is also used as the heating element as strange as that
> sounds. There are only 2 connections to the tip and it provides both
> heating and temperature measurement.
>
> I am testing on my bench and applying 12v getting it hot then connecting to
> the op-amp and reading the output and has survived many cycles. And
> convinced its a thermocouple as reversing the connections to the op amp has
> the expected outcome. I am so tempted to connect the 12v while connected
> to the opamp ( I found a spare) as it is protected by the 2 x 1k ohm input
> resistors but I will heed your advice.
>
> This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed engineered the
> same station I have. On closer inspection I don't see the disconnect when
> heating. I was sure that schematic had a disconnect transistor to protect
> the opamp, I will have to watch again.
>
> That station is ok, except I want a web page to tweak all the PID constants
> and a rotary encoder with OLED display for fast temperature adjustment. It
> currently has a weird insert card and clunky non-intuitive buttons for temp
> adjust.
>
> All is tested ok, my code supports MAX6675, DHT, thermistors and 4diodes in
> series and is used at home to make black garlic where the humidity is
> maintained with a peristaltic pump etc among other things
>
> A very early version can be seen here
> https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
>
> I now want to leverage of all that development and control a soldering iron
> the way I want it. Fast heating, setable standby temp, easy adjust, just
> need to do the last bit.
>
> Cheers Justin
>
> On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email] wrote:
>
> > I think perhaps you've got a few misconceptions here.
> > Thermocouple usually refers to a dissimilar metal junction sensor, applying
> > heat to it creates a voltage across the two wire ends*, you don't feed
> > power to a thermocouple.
> > Most chip datasheets specify the maximum input voltage in relation to VCC,
> > your GL358 (if I'm reading the datasheet right) will be able to cope with
> > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V, 32V will
> > probably release the magic smoke.
> > *Thermocouples are really useful, put enough of them in series and apply
> > fire, you can charge a car battery!!!
> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> > On Sat, 12 Sep 2020 at 10:00, Justin Richards [hidden email]
> > wrote:
> >
> > > Experimenting with using a ESP8266 as a soldering iron PID controller
> > > driving the ADC with the output of an opamp.
> > > The GL358 opamp datasheet specifies max differential input voltage as
> > > 32V.
> > > I would like to know if that is as it sounds and I can force the inputs
> > > to
> > > have a max of 32v across them with a single supply to the Opamp of +5V.
> > > I
> > > am still learning about opamps and thought the inputs were to be
> > > considered
> > > as a virtual ground and they will effectively be at the same potential
> > > but
> > > here i would be brute forcing a voltage across them and concerned it may
> > > be
> > > damaging and bad practice.
> > > The GL358 (was in the junk box) is configured as a dual amp to amplify
> > > the
> > > thermocouple (integral part of soldering tip) output of approx 2mV - 8mV
> > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > One side of the thermocouple is grounded and connected via a resistor to
> > > the inverting input while the other side is connected via another
> > > resistor to the non-inverting input.
> > > I plan to measure temperature then apply 24V across the thermocouple.
> > > which
> > > will drive 24V across the two 1k ohm opamp input resistors.
> > > As a caution I plan to have back to back diodes at the inputs to limit
> > > the
> > > voltage across them to approx 0.7v.
> > > But back to the original question, are the protection diodes needed
> > > given a
> > > maximum differential voltage of 32 volts or is that only if the supply is
> > > also at 32V.
> > > I found a design that disconnects the thermocouple from the opamp during
> > > heating but not sure if that is actually required and obviously
> > > simplifies
> > > the design if not.
> > >
> > > Regards
> > > Justin
> > >
> > > ---------------
> > >
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> >
> > --
> > Clint. M0UAW IO83
> >
> > No trees were harmed in the sending of this mail. However, a large number
> > of electrons were greatly inconvenienced.
> > -------------------------------------------------------------------------------------------------------------------
> >
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist



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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards
Is that link broken?  I get a 404 error.

On power from thermocouple stacks, I lived in a house for awhile with a furnace that used a thrermopile (lots of thermocouples in series) to power/drive the gas valve through the thermostat.


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 5:53 AM, Justin Richards <[hidden email]> wrote:

> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
>
> That made for an interesting read, some clever designs. I did not know
> RTG's used heat this way.
>
> ---------------------------------------------------------------------------------------------------
>
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist



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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards
Couldn't find the schematic, but the manual for that iron does have the iron pinout.  Normally it has a built in thermistor for temperature sensing (the 5 pin connector has 2 pins for the thermistor, 2 for heater, and one for ground  see this <https://runawaybrainz.blogspot.com/2014/08/hakko-fx888d-din-connector-pinouts.html> or the manual.  It's possible to only use 2 wires and use the heating element itself as a thermistor, as in the article for Steve Circa I mentioned earlier.  I can't find a readable schematic for that station.


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 5:53 AM, Justin Richards <[hidden email]> wrote:

> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
>
> That made for an interesting read, some clever designs. I did not know
> RTG's used heat this way.
>
> ---------------------------------------------------------------------------------------------------
>
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist



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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
In reply to this post by madscientistatlarge
I am reasonably certain these are thermocouples.  If I heat it up and
connect it to my multimeter it reads about 8mV and drifts down to about
2mV.  I dont think a thermistor would do that.  It reads about 8 ohms when
measuring resistance.

I suspect built into the tip is heating elements that are in series
with the thermocouple and make up each arm of the thermocouple.

There was a x-ray of a soldering iron tip but I am having trouble finding
it.



On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
[hidden email]> wrote:

> A thermistor is not a thermocouple.  You could never put a thermocouple
> across the heating element, thermocouples have very low resistance, it
> would pop like a fuse if you put voltage on it, they are normally connected
> to a very high resistance.  Thermocouples produce mV of output, the op amp
> you want to use has a high input offset and high input offset drift, it
> would completely obscure the the actual input voltage.
>
> I think that station monitors the resistance of the element, after briefly
> disconnecting it from the power supply. Something like this <
> https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> >
>
>
> Sent with ProtonMail Secure Email.
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> [hidden email]> wrote:
>
> > Hi Clint,
> >
> > yes, thermocouples are as you say but with the T12 style soldering tips
> the
> > thermocouple is also used as the heating element as strange as that
> > sounds. There are only 2 connections to the tip and it provides both
> > heating and temperature measurement.
> >
> > I am testing on my bench and applying 12v getting it hot then connecting
> to
> > the op-amp and reading the output and has survived many cycles. And
> > convinced its a thermocouple as reversing the connections to the op amp
> has
> > the expected outcome. I am so tempted to connect the 12v while connected
> > to the opamp ( I found a spare) as it is protected by the 2 x 1k ohm
> input
> > resistors but I will heed your advice.
> >
> > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed engineered
> the
> > same station I have. On closer inspection I don't see the disconnect when
> > heating. I was sure that schematic had a disconnect transistor to protect
> > the opamp, I will have to watch again.
> >
> > That station is ok, except I want a web page to tweak all the PID
> constants
> > and a rotary encoder with OLED display for fast temperature adjustment.
> It
> > currently has a weird insert card and clunky non-intuitive buttons for
> temp
> > adjust.
> >
> > All is tested ok, my code supports MAX6675, DHT, thermistors and 4diodes
> in
> > series and is used at home to make black garlic where the humidity is
> > maintained with a peristaltic pump etc among other things
> >
> > A very early version can be seen here
> >
> https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> >
> > I now want to leverage of all that development and control a soldering
> iron
> > the way I want it. Fast heating, setable standby temp, easy adjust, just
> > need to do the last bit.
> >
> > Cheers Justin
> >
> > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email] wrote:
> >
> > > I think perhaps you've got a few misconceptions here.
> > > Thermocouple usually refers to a dissimilar metal junction sensor,
> applying
> > > heat to it creates a voltage across the two wire ends*, you don't feed
> > > power to a thermocouple.
> > > Most chip datasheets specify the maximum input voltage in relation to
> VCC,
> > > your GL358 (if I'm reading the datasheet right) will be able to cope
> with
> > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V, 32V
> will
> > > probably release the magic smoke.
> > > *Thermocouples are really useful, put enough of them in series and
> apply
> > > fire, you can charge a car battery!!!
> > >
> http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> [hidden email]
> > > wrote:
> > >
> > > > Experimenting with using a ESP8266 as a soldering iron PID controller
> > > > driving the ADC with the output of an opamp.
> > > > The GL358 opamp datasheet specifies max differential input voltage as
> > > > 32V.
> > > > I would like to know if that is as it sounds and I can force the
> inputs
> > > > to
> > > > have a max of 32v across them with a single supply to the Opamp of
> +5V.
> > > > I
> > > > am still learning about opamps and thought the inputs were to be
> > > > considered
> > > > as a virtual ground and they will effectively be at the same
> potential
> > > > but
> > > > here i would be brute forcing a voltage across them and concerned it
> may
> > > > be
> > > > damaging and bad practice.
> > > > The GL358 (was in the junk box) is configured as a dual amp to
> amplify
> > > > the
> > > > thermocouple (integral part of soldering tip) output of approx 2mV -
> 8mV
> > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > One side of the thermocouple is grounded and connected via a
> resistor to
> > > > the inverting input while the other side is connected via another
> > > > resistor to the non-inverting input.
> > > > I plan to measure temperature then apply 24V across the thermocouple.
> > > > which
> > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > As a caution I plan to have back to back diodes at the inputs to
> limit
> > > > the
> > > > voltage across them to approx 0.7v.
> > > > But back to the original question, are the protection diodes needed
> > > > given a
> > > > maximum differential voltage of 32 volts or is that only if the
> supply is
> > > > also at 32V.
> > > > I found a design that disconnects the thermocouple from the opamp
> during
> > > > heating but not sure if that is actually required and obviously
> > > > simplifies
> > > > the design if not.
> > > >
> > > > Regards
> > > > Justin
> > > >
> > > > ---------------
> > > >
> > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > View/change your membership options at
> > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
> > > --
> > > Clint. M0UAW IO83
> > >
> > > No trees were harmed in the sending of this mail. However, a large
> number
> > > of electrons were greatly inconvenienced.
> > >
> -------------------------------------------------------------------------------------------------------------------
> > >
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> >
> > --
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
Please see the manual <https://doc.hakko.com/download.php?_gs=on&l=en&kp=fx888d&d=5680>  It shows the pinout of the iron, and very, very clearly shows the temperature sensor does not share any pins with the heater.  It also shows the resistance of the element and the sensor.  It is a thermistor.  If it were a thermocouple the voltage wouldn't drop when the iron heated.  I suspect you measured poorly/got interferance picked up.  mv signals in that range, when anywhere near power line connections/transformers can be from capacitive coupling.  Also what meter did you use?  I believe you are on a snipe hunt, having been misled.


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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 6:51 AM, Justin Richards <[hidden email]> wrote:

> I am reasonably certain these are thermocouples. If I heat it up and
> connect it to my multimeter it reads about 8mV and drifts down to about
> 2mV. I dont think a thermistor would do that. It reads about 8 ohms when
> measuring resistance.
>
> I suspect built into the tip is heating elements that are in series
> with the thermocouple and make up each arm of the thermocouple.
>
> There was a x-ray of a soldering iron tip but I am having trouble finding
> it.
>
> On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
> [hidden email]> wrote:
>
> > A thermistor is not a thermocouple. You could never put a thermocouple
> > across the heating element, thermocouples have very low resistance, it
> > would pop like a fuse if you put voltage on it, they are normally connected
> > to a very high resistance. Thermocouples produce mV of output, the op amp
> > you want to use has a high input offset and high input offset drift, it
> > would completely obscure the the actual input voltage.
> > I think that station monitors the resistance of the element, after briefly
> > disconnecting it from the power supply. Something like this <
> > https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> >
> > >
> >
> > Sent with ProtonMail Secure Email.
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> > [hidden email]> wrote:
> >
> > > Hi Clint,
> > > yes, thermocouples are as you say but with the T12 style soldering tips
> > > the
> > > thermocouple is also used as the heating element as strange as that
> > > sounds. There are only 2 connections to the tip and it provides both
> > > heating and temperature measurement.
> > > I am testing on my bench and applying 12v getting it hot then connecting
> > > to
> > > the op-amp and reading the output and has survived many cycles. And
> > > convinced its a thermocouple as reversing the connections to the op amp
> > > has
> > > the expected outcome. I am so tempted to connect the 12v while connected
> > > to the opamp ( I found a spare) as it is protected by the 2 x 1k ohm
> > > input
> > > resistors but I will heed your advice.
> > > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed engineered
> > > the
> > > same station I have. On closer inspection I don't see the disconnect when
> > > heating. I was sure that schematic had a disconnect transistor to protect
> > > the opamp, I will have to watch again.
> > > That station is ok, except I want a web page to tweak all the PID
> > > constants
> > > and a rotary encoder with OLED display for fast temperature adjustment.
> > > It
> > > currently has a weird insert card and clunky non-intuitive buttons for
> > > temp
> > > adjust.
> > > All is tested ok, my code supports MAX6675, DHT, thermistors and 4diodes
> > > in
> > > series and is used at home to make black garlic where the humidity is
> > > maintained with a peristaltic pump etc among other things
> > > A very early version can be seen here
> >
> > https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> >
> > > I now want to leverage of all that development and control a soldering
> > > iron
> > > the way I want it. Fast heating, setable standby temp, easy adjust, just
> > > need to do the last bit.
> > > Cheers Justin
> > > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email] wrote:
> > >
> > > > I think perhaps you've got a few misconceptions here.
> > > > Thermocouple usually refers to a dissimilar metal junction sensor,
> > > > applying
> > >
> > > > heat to it creates a voltage across the two wire ends*, you don't feed
> > > > power to a thermocouple.
> > > > Most chip datasheets specify the maximum input voltage in relation to
> > > > VCC,
> > >
> > > > your GL358 (if I'm reading the datasheet right) will be able to cope
> > > > with
> > >
> > > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V, 32V
> > > > will
> > >
> > > > probably release the magic smoke.
> > > > *Thermocouples are really useful, put enough of them in series and
> > > > apply
> > >
> > > > fire, you can charge a car battery!!!
> >
> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> >
> > > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> > > > [hidden email]
> > >
> > > > wrote:
> > > >
> > > > > Experimenting with using a ESP8266 as a soldering iron PID controller
> > > > > driving the ADC with the output of an opamp.
> > > > > The GL358 opamp datasheet specifies max differential input voltage as
> > > > > 32V.
> > > > > I would like to know if that is as it sounds and I can force the
> > > > > inputs
> > >
> > > > > to
> > > > > have a max of 32v across them with a single supply to the Opamp of
> > > > > +5V.
> > >
> > > > > I
> > > > > am still learning about opamps and thought the inputs were to be
> > > > > considered
> > > > > as a virtual ground and they will effectively be at the same
> > > > > potential
> > >
> > > > > but
> > > > > here i would be brute forcing a voltage across them and concerned it
> > > > > may
> > >
> > > > > be
> > > > > damaging and bad practice.
> > > > > The GL358 (was in the junk box) is configured as a dual amp to
> > > > > amplify
> > >
> > > > > the
> > > > > thermocouple (integral part of soldering tip) output of approx 2mV -
> > > > > 8mV
> > >
> > > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > > One side of the thermocouple is grounded and connected via a
> > > > > resistor to
> > >
> > > > > the inverting input while the other side is connected via another
> > > > > resistor to the non-inverting input.
> > > > > I plan to measure temperature then apply 24V across the thermocouple.
> > > > > which
> > > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > > As a caution I plan to have back to back diodes at the inputs to
> > > > > limit
> > >
> > > > > the
> > > > > voltage across them to approx 0.7v.
> > > > > But back to the original question, are the protection diodes needed
> > > > > given a
> > > > > maximum differential voltage of 32 volts or is that only if the
> > > > > supply is
> > >
> > > > > also at 32V.
> > > > > I found a design that disconnects the thermocouple from the opamp
> > > > > during
> > >
> > > > > heating but not sure if that is actually required and obviously
> > > > > simplifies
> > > > > the design if not.
> > > > > Regards
> > > > > Justin
> > > > >
> > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > View/change your membership options at
> > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > >
> > > > --
> > > > Clint. M0UAW IO83
> > > > No trees were harmed in the sending of this mail. However, a large
> > > > number
> > >
> > > > of electrons were greatly inconvenienced.
> >
> > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > View/change your membership options at
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> > >
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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
In reply to this post by madscientistatlarge
The station you link to uses a different style of tip T18 series where the
element is not part of the tip but rather the heating element is the
traditional setup with what I suspect is a separate element and separate
thermistor which are slow to respond and suffer more from over shoot.

The FX-951 uses the T12 tips that incorp the thermocouple and element into
the tip.  They cant be separated, directly connected and integral to the
tip and therefore can be more tightly controlled. There are only 2 possible
electrical connections.  The outer shield is not in any way connected to
the other two connections.  It reads open circuit.

There are many projects that treat the T12 tips as thermocouples.  There is
some debate regarding the type.  Most have assumed type K but some believe
these tips better fit a type C profile.  If I plug my tip into the Fluke 87
in temperature mode, it seems to read a bit low.  I initially dismissed
this as bogus connections but it seems to fit the type C thermocouple
tables.  eg at 1000oC K is about 42mV wheres type C is about 18mV,  Type C
also fits with my approx value of 8mV for 400oC

Back to the original question, i found some datasheets that state a max
input current of 50mA, so if i size the input resistors correctly and use
diodes to clamp the input, I think it should be possible to minimise the
input current and protect the opamp. 6k ohms on each input should limit the
current to around 5mA assuming a max driving voltage of 30v.  I intend to
use 24V, I see someone has direct connected to a solar panel. that would
nominally have Voc of 21V.


On Sat, Sep 12, 2020 at 8:45 PM madscientistatlarge <
[hidden email]> wrote:

> Couldn't find the schematic, but the manual for that iron does have the
> iron pinout.  Normally it has a built in thermistor for temperature sensing
> (the 5 pin connector has 2 pins for the thermistor, 2 for heater, and one
> for ground  see this <
> https://runawaybrainz.blogspot.com/2014/08/hakko-fx888d-din-connector-pinouts.html>
> or the manual.  It's possible to only use 2 wires and use the heating
> element itself as a thermistor, as in the article for Steve Circa I
> mentioned earlier.  I can't find a readable schematic for that station.
>
>
> Sent with ProtonMail Secure Email.
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Saturday, September 12, 2020 5:53 AM, Justin Richards <
> [hidden email]> wrote:
>
> > >
> http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> >
> > That made for an interesting read, some clever designs. I did not know
> > RTG's used heat this way.
> >
> >
> ---------------------------------------------------------------------------------------------------
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards

That resistance is wrong according to the manual which says  ohms for the sensor and 2 ohms or less for the heater.  Have you connected any of the wires together?  If you directly put a power supply across the sensor it was likely damaged.  It has a 6 pin plug on it originally, Yes?  Thermocouples are very unlikely to share any wire/pin with the heater, it would make the measurement very noisy etc.  You could email Hakko and ask them what kind of sensor it is.  They apparently have removed the schematics from other websites but are likely willing to tell you what kind of sensor it is and what pins it's normally connected to.  The sensor should be between the two blue wires and it likely is a thermocouple, but somethings gone wrong.  Again, it's all in the instruction manual.


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 6:51 AM, Justin Richards <[hidden email]> wrote:

> I am reasonably certain these are thermocouples. If I heat it up and
> connect it to my multimeter it reads about 8mV and drifts down to about
> 2mV. I dont think a thermistor would do that. It reads about 8 ohms when
> measuring resistance.
>
> I suspect built into the tip is heating elements that are in series
> with the thermocouple and make up each arm of the thermocouple.
>
> There was a x-ray of a soldering iron tip but I am having trouble finding
> it.
>
> On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
> [hidden email]> wrote:
>
> > A thermistor is not a thermocouple. You could never put a thermocouple
> > across the heating element, thermocouples have very low resistance, it
> > would pop like a fuse if you put voltage on it, they are normally connected
> > to a very high resistance. Thermocouples produce mV of output, the op amp
> > you want to use has a high input offset and high input offset drift, it
> > would completely obscure the the actual input voltage.
> > I think that station monitors the resistance of the element, after briefly
> > disconnecting it from the power supply. Something like this <
> > https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> >
> > >
> >
> > Sent with ProtonMail Secure Email.
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> > [hidden email]> wrote:
> >
> > > Hi Clint,
> > > yes, thermocouples are as you say but with the T12 style soldering tips
> > > the
> > > thermocouple is also used as the heating element as strange as that
> > > sounds. There are only 2 connections to the tip and it provides both
> > > heating and temperature measurement.
> > > I am testing on my bench and applying 12v getting it hot then connecting
> > > to
> > > the op-amp and reading the output and has survived many cycles. And
> > > convinced its a thermocouple as reversing the connections to the op amp
> > > has
> > > the expected outcome. I am so tempted to connect the 12v while connected
> > > to the opamp ( I found a spare) as it is protected by the 2 x 1k ohm
> > > input
> > > resistors but I will heed your advice.
> > > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed engineered
> > > the
> > > same station I have. On closer inspection I don't see the disconnect when
> > > heating. I was sure that schematic had a disconnect transistor to protect
> > > the opamp, I will have to watch again.
> > > That station is ok, except I want a web page to tweak all the PID
> > > constants
> > > and a rotary encoder with OLED display for fast temperature adjustment.
> > > It
> > > currently has a weird insert card and clunky non-intuitive buttons for
> > > temp
> > > adjust.
> > > All is tested ok, my code supports MAX6675, DHT, thermistors and 4diodes
> > > in
> > > series and is used at home to make black garlic where the humidity is
> > > maintained with a peristaltic pump etc among other things
> > > A very early version can be seen here
> >
> > https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> >
> > > I now want to leverage of all that development and control a soldering
> > > iron
> > > the way I want it. Fast heating, setable standby temp, easy adjust, just
> > > need to do the last bit.
> > > Cheers Justin
> > > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email] wrote:
> > >
> > > > I think perhaps you've got a few misconceptions here.
> > > > Thermocouple usually refers to a dissimilar metal junction sensor,
> > > > applying
> > >
> > > > heat to it creates a voltage across the two wire ends*, you don't feed
> > > > power to a thermocouple.
> > > > Most chip datasheets specify the maximum input voltage in relation to
> > > > VCC,
> > >
> > > > your GL358 (if I'm reading the datasheet right) will be able to cope
> > > > with
> > >
> > > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V, 32V
> > > > will
> > >
> > > > probably release the magic smoke.
> > > > *Thermocouples are really useful, put enough of them in series and
> > > > apply
> > >
> > > > fire, you can charge a car battery!!!
> >
> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> >
> > > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> > > > [hidden email]
> > >
> > > > wrote:
> > > >
> > > > > Experimenting with using a ESP8266 as a soldering iron PID controller
> > > > > driving the ADC with the output of an opamp.
> > > > > The GL358 opamp datasheet specifies max differential input voltage as
> > > > > 32V.
> > > > > I would like to know if that is as it sounds and I can force the
> > > > > inputs
> > >
> > > > > to
> > > > > have a max of 32v across them with a single supply to the Opamp of
> > > > > +5V.
> > >
> > > > > I
> > > > > am still learning about opamps and thought the inputs were to be
> > > > > considered
> > > > > as a virtual ground and they will effectively be at the same
> > > > > potential
> > >
> > > > > but
> > > > > here i would be brute forcing a voltage across them and concerned it
> > > > > may
> > >
> > > > > be
> > > > > damaging and bad practice.
> > > > > The GL358 (was in the junk box) is configured as a dual amp to
> > > > > amplify
> > >
> > > > > the
> > > > > thermocouple (integral part of soldering tip) output of approx 2mV -
> > > > > 8mV
> > >
> > > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > > One side of the thermocouple is grounded and connected via a
> > > > > resistor to
> > >
> > > > > the inverting input while the other side is connected via another
> > > > > resistor to the non-inverting input.
> > > > > I plan to measure temperature then apply 24V across the thermocouple.
> > > > > which
> > > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > > As a caution I plan to have back to back diodes at the inputs to
> > > > > limit
> > >
> > > > > the
> > > > > voltage across them to approx 0.7v.
> > > > > But back to the original question, are the protection diodes needed
> > > > > given a
> > > > > maximum differential voltage of 32 volts or is that only if the
> > > > > supply is
> > >
> > > > > also at 32V.
> > > > > I found a design that disconnects the thermocouple from the opamp
> > > > > during
> > >
> > > > > heating but not sure if that is actually required and obviously
> > > > > simplifies
> > > > > the design if not.
> > > > > Regards
> > > > > Justin
> > > > >
> > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > View/change your membership options at
> > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > >
> > > > --
> > > > Clint. M0UAW IO83
> > > > No trees were harmed in the sending of this mail. However, a large
> > > > number
> > >
> > > > of electrons were greatly inconvenienced.
> >
> > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > View/change your membership options at
> > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
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> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> >
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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
In reply to this post by madscientistatlarge
> were a thermocouple the voltage wouldn't drop when the iron heated.  I
> suspect you measured poorly/got interferance picked up.  mv signals in that
> Sent with ProtonMail Secure Email.
>

It was my intention to state that when heated and measured it starts out
reading 8mV then drops to around 2mV as it cools.
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards
Do the tips look like this <https://www.amazon.com/Soldering-Station-Solder-Replacement-FX-951/dp/B07FYV7ZV8>?  In which case there are 3 connections, 2 would be for the heater and one would be for a thermisor with one wire shared.  This would have to be a thermistor, a thermocouple would work very, very poorly in this case.


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 6:51 AM, Justin Richards <[hidden email]> wrote:

> I am reasonably certain these are thermocouples. If I heat it up and
> connect it to my multimeter it reads about 8mV and drifts down to about
> 2mV. I dont think a thermistor would do that. It reads about 8 ohms when
> measuring resistance.
>
> I suspect built into the tip is heating elements that are in series
> with the thermocouple and make up each arm of the thermocouple.
>
> There was a x-ray of a soldering iron tip but I am having trouble finding
> it.
>
> On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
> [hidden email]> wrote:
>
> > A thermistor is not a thermocouple. You could never put a thermocouple
> > across the heating element, thermocouples have very low resistance, it
> > would pop like a fuse if you put voltage on it, they are normally connected
> > to a very high resistance. Thermocouples produce mV of output, the op amp
> > you want to use has a high input offset and high input offset drift, it
> > would completely obscure the the actual input voltage.
> > I think that station monitors the resistance of the element, after briefly
> > disconnecting it from the power supply. Something like this <
> > https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> >
> > >
> >
> > Sent with ProtonMail Secure Email.
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> > [hidden email]> wrote:
> >
> > > Hi Clint,
> > > yes, thermocouples are as you say but with the T12 style soldering tips
> > > the
> > > thermocouple is also used as the heating element as strange as that
> > > sounds. There are only 2 connections to the tip and it provides both
> > > heating and temperature measurement.
> > > I am testing on my bench and applying 12v getting it hot then connecting
> > > to
> > > the op-amp and reading the output and has survived many cycles. And
> > > convinced its a thermocouple as reversing the connections to the op amp
> > > has
> > > the expected outcome. I am so tempted to connect the 12v while connected
> > > to the opamp ( I found a spare) as it is protected by the 2 x 1k ohm
> > > input
> > > resistors but I will heed your advice.
> > > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed engineered
> > > the
> > > same station I have. On closer inspection I don't see the disconnect when
> > > heating. I was sure that schematic had a disconnect transistor to protect
> > > the opamp, I will have to watch again.
> > > That station is ok, except I want a web page to tweak all the PID
> > > constants
> > > and a rotary encoder with OLED display for fast temperature adjustment.
> > > It
> > > currently has a weird insert card and clunky non-intuitive buttons for
> > > temp
> > > adjust.
> > > All is tested ok, my code supports MAX6675, DHT, thermistors and 4diodes
> > > in
> > > series and is used at home to make black garlic where the humidity is
> > > maintained with a peristaltic pump etc among other things
> > > A very early version can be seen here
> >
> > https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> >
> > > I now want to leverage of all that development and control a soldering
> > > iron
> > > the way I want it. Fast heating, setable standby temp, easy adjust, just
> > > need to do the last bit.
> > > Cheers Justin
> > > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email] wrote:
> > >
> > > > I think perhaps you've got a few misconceptions here.
> > > > Thermocouple usually refers to a dissimilar metal junction sensor,
> > > > applying
> > >
> > > > heat to it creates a voltage across the two wire ends*, you don't feed
> > > > power to a thermocouple.
> > > > Most chip datasheets specify the maximum input voltage in relation to
> > > > VCC,
> > >
> > > > your GL358 (if I'm reading the datasheet right) will be able to cope
> > > > with
> > >
> > > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V, 32V
> > > > will
> > >
> > > > probably release the magic smoke.
> > > > *Thermocouples are really useful, put enough of them in series and
> > > > apply
> > >
> > > > fire, you can charge a car battery!!!
> >
> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> >
> > > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> > > > [hidden email]
> > >
> > > > wrote:
> > > >
> > > > > Experimenting with using a ESP8266 as a soldering iron PID controller
> > > > > driving the ADC with the output of an opamp.
> > > > > The GL358 opamp datasheet specifies max differential input voltage as
> > > > > 32V.
> > > > > I would like to know if that is as it sounds and I can force the
> > > > > inputs
> > >
> > > > > to
> > > > > have a max of 32v across them with a single supply to the Opamp of
> > > > > +5V.
> > >
> > > > > I
> > > > > am still learning about opamps and thought the inputs were to be
> > > > > considered
> > > > > as a virtual ground and they will effectively be at the same
> > > > > potential
> > >
> > > > > but
> > > > > here i would be brute forcing a voltage across them and concerned it
> > > > > may
> > >
> > > > > be
> > > > > damaging and bad practice.
> > > > > The GL358 (was in the junk box) is configured as a dual amp to
> > > > > amplify
> > >
> > > > > the
> > > > > thermocouple (integral part of soldering tip) output of approx 2mV -
> > > > > 8mV
> > >
> > > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > > One side of the thermocouple is grounded and connected via a
> > > > > resistor to
> > >
> > > > > the inverting input while the other side is connected via another
> > > > > resistor to the non-inverting input.
> > > > > I plan to measure temperature then apply 24V across the thermocouple.
> > > > > which
> > > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > > As a caution I plan to have back to back diodes at the inputs to
> > > > > limit
> > >
> > > > > the
> > > > > voltage across them to approx 0.7v.
> > > > > But back to the original question, are the protection diodes needed
> > > > > given a
> > > > > maximum differential voltage of 32 volts or is that only if the
> > > > > supply is
> > >
> > > > > also at 32V.
> > > > > I found a design that disconnects the thermocouple from the opamp
> > > > > during
> > >
> > > > > heating but not sure if that is actually required and obviously
> > > > > simplifies
> > > > > the design if not.
> > > > > Regards
> > > > > Justin
> > > > >
> > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > View/change your membership options at
> > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > >
> > > > --
> > > > Clint. M0UAW IO83
> > > > No trees were harmed in the sending of this mail. However, a large
> > > > number
> > >
> > > > of electrons were greatly inconvenienced.
> >
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> > > > View/change your membership options at
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> > >
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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
In reply to this post by madscientistatlarge
We are talking about completely different irons and stations.  If you
google images of the T12 tip you will see that there just isnt the number
of connections you are suggesting,

In my hakko there is only 2 wires going from the circuit board to the
plug.  If you had a close look of the FX-951 tear down and reverse
engineering that I originally linked to you would see this.  There is no
measurable connection between the outer cas and the two ring-contacts.

This describes the T12 and indicates the sensor is infact a thermocouple
http://redlightgreen.org/2019/09/obzor-nabora-vysokokachestvennyh-pajalnyh-zhal-t12/


I had to google snip hunt.

>
> That resistance is wrong according to the manual which says  ohms for the
> sensor and 2 ohms or less for the heater.  Have you connected any of the
> wires together?  If you directly put a power supply across the sensor it
> was likely damaged.  It has a 6 pin plug on it originally, Yes?
> Thermocouples are very unlikely to share any wire/pin with the heater, it
> would make the measurement very noisy etc.  You could email Hakko and ask
> them what kind of sensor it is.  They apparently have removed the
> schematics from other websites but are likely willing to tell you what kind
> of sensor it is and what pins it's normally connected to.  The sensor
> should be between the two blue wires and it likely is a thermocouple, but
> somethings gone wrong.  Again, it's all in the instruction manual.
>
>
> Sent with ProtonMail Secure Email.
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Saturday, September 12, 2020 6:51 AM, Justin Richards <
> [hidden email]> wrote:
>
> > I am reasonably certain these are thermocouples. If I heat it up and
> > connect it to my multimeter it reads about 8mV and drifts down to about
> > 2mV. I dont think a thermistor would do that. It reads about 8 ohms when
> > measuring resistance.
> >
> > I suspect built into the tip is heating elements that are in series
> > with the thermocouple and make up each arm of the thermocouple.
> >
> > There was a x-ray of a soldering iron tip but I am having trouble finding
> > it.
> >
> > On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
> > [hidden email]> wrote:
> >
> > > A thermistor is not a thermocouple. You could never put a thermocouple
> > > across the heating element, thermocouples have very low resistance, it
> > > would pop like a fuse if you put voltage on it, they are normally
> connected
> > > to a very high resistance. Thermocouples produce mV of output, the op
> amp
> > > you want to use has a high input offset and high input offset drift, it
> > > would completely obscure the the actual input voltage.
> > > I think that station monitors the resistance of the element, after
> briefly
> > > disconnecting it from the power supply. Something like this <
> > >
> https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> > >
> > > >
> > >
> > > Sent with ProtonMail Secure Email.
> > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> > > [hidden email]> wrote:
> > >
> > > > Hi Clint,
> > > > yes, thermocouples are as you say but with the T12 style soldering
> tips
> > > > the
> > > > thermocouple is also used as the heating element as strange as that
> > > > sounds. There are only 2 connections to the tip and it provides both
> > > > heating and temperature measurement.
> > > > I am testing on my bench and applying 12v getting it hot then
> connecting
> > > > to
> > > > the op-amp and reading the output and has survived many cycles. And
> > > > convinced its a thermocouple as reversing the connections to the op
> amp
> > > > has
> > > > the expected outcome. I am so tempted to connect the 12v while
> connected
> > > > to the opamp ( I found a spare) as it is protected by the 2 x 1k ohm
> > > > input
> > > > resistors but I will heed your advice.
> > > > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed
> engineered
> > > > the
> > > > same station I have. On closer inspection I don't see the disconnect
> when
> > > > heating. I was sure that schematic had a disconnect transistor to
> protect
> > > > the opamp, I will have to watch again.
> > > > That station is ok, except I want a web page to tweak all the PID
> > > > constants
> > > > and a rotary encoder with OLED display for fast temperature
> adjustment.
> > > > It
> > > > currently has a weird insert card and clunky non-intuitive buttons
> for
> > > > temp
> > > > adjust.
> > > > All is tested ok, my code supports MAX6675, DHT, thermistors and
> 4diodes
> > > > in
> > > > series and is used at home to make black garlic where the humidity is
> > > > maintained with a peristaltic pump etc among other things
> > > > A very early version can be seen here
> > >
> > >
> https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> > >
> > > > I now want to leverage of all that development and control a
> soldering
> > > > iron
> > > > the way I want it. Fast heating, setable standby temp, easy adjust,
> just
> > > > need to do the last bit.
> > > > Cheers Justin
> > > > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email] wrote:
> > > >
> > > > > I think perhaps you've got a few misconceptions here.
> > > > > Thermocouple usually refers to a dissimilar metal junction sensor,
> > > > > applying
> > > >
> > > > > heat to it creates a voltage across the two wire ends*, you don't
> feed
> > > > > power to a thermocouple.
> > > > > Most chip datasheets specify the maximum input voltage in relation
> to
> > > > > VCC,
> > > >
> > > > > your GL358 (if I'm reading the datasheet right) will be able to
> cope
> > > > > with
> > > >
> > > > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V,
> 32V
> > > > > will
> > > >
> > > > > probably release the magic smoke.
> > > > > *Thermocouples are really useful, put enough of them in series and
> > > > > apply
> > > >
> > > > > fire, you can charge a car battery!!!
> > >
> > >
> http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> > >
> > > > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> > > > > [hidden email]
> > > >
> > > > > wrote:
> > > > >
> > > > > > Experimenting with using a ESP8266 as a soldering iron PID
> controller
> > > > > > driving the ADC with the output of an opamp.
> > > > > > The GL358 opamp datasheet specifies max differential input
> voltage as
> > > > > > 32V.
> > > > > > I would like to know if that is as it sounds and I can force the
> > > > > > inputs
> > > >
> > > > > > to
> > > > > > have a max of 32v across them with a single supply to the Opamp
> of
> > > > > > +5V.
> > > >
> > > > > > I
> > > > > > am still learning about opamps and thought the inputs were to be
> > > > > > considered
> > > > > > as a virtual ground and they will effectively be at the same
> > > > > > potential
> > > >
> > > > > > but
> > > > > > here i would be brute forcing a voltage across them and
> concerned it
> > > > > > may
> > > >
> > > > > > be
> > > > > > damaging and bad practice.
> > > > > > The GL358 (was in the junk box) is configured as a dual amp to
> > > > > > amplify
> > > >
> > > > > > the
> > > > > > thermocouple (integral part of soldering tip) output of approx
> 2mV -
> > > > > > 8mV
> > > >
> > > > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > > > One side of the thermocouple is grounded and connected via a
> > > > > > resistor to
> > > >
> > > > > > the inverting input while the other side is connected via another
> > > > > > resistor to the non-inverting input.
> > > > > > I plan to measure temperature then apply 24V across the
> thermocouple.
> > > > > > which
> > > > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > > > As a caution I plan to have back to back diodes at the inputs to
> > > > > > limit
> > > >
> > > > > > the
> > > > > > voltage across them to approx 0.7v.
> > > > > > But back to the original question, are the protection diodes
> needed
> > > > > > given a
> > > > > > maximum differential voltage of 32 volts or is that only if the
> > > > > > supply is
> > > >
> > > > > > also at 32V.
> > > > > > I found a design that disconnects the thermocouple from the opamp
> > > > > > during
> > > >
> > > > > > heating but not sure if that is actually required and obviously
> > > > > > simplifies
> > > > > > the design if not.
> > > > > > Regards
> > > > > > Justin
> > > > > >
> > > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > > View/change your membership options at
> > > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > > >
> > > > > --
> > > > > Clint. M0UAW IO83
> > > > > No trees were harmed in the sending of this mail. However, a large
> > > > > number
> > > >
> > > > > of electrons were greatly inconvenienced.
> > >
> > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > View/change your membership options at
> > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > >
> > > > --
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> > > > View/change your membership options at
> > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
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>
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards
here's a link for a home made controller for the t12.  <https://www.hackster.io/sfrwmaker/soldering-iron-controller-for-hakko-t12-tips-on-arduino-f7a888>  Apparently it is a thermocouple and shares the ground line, this is a very bad design.  Hacko discontinued it a long time ago though I know clones are still being made.


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 7:43 AM, Justin Richards <[hidden email]> wrote:

> The station you link to uses a different style of tip T18 series where the
> element is not part of the tip but rather the heating element is the
> traditional setup with what I suspect is a separate element and separate
> thermistor which are slow to respond and suffer more from over shoot.
>
> The FX-951 uses the T12 tips that incorp the thermocouple and element into
> the tip. They cant be separated, directly connected and integral to the
> tip and therefore can be more tightly controlled. There are only 2 possible
> electrical connections. The outer shield is not in any way connected to
> the other two connections. It reads open circuit.
>
> There are many projects that treat the T12 tips as thermocouples. There is
> some debate regarding the type. Most have assumed type K but some believe
> these tips better fit a type C profile. If I plug my tip into the Fluke 87
> in temperature mode, it seems to read a bit low. I initially dismissed
> this as bogus connections but it seems to fit the type C thermocouple
> tables. eg at 1000oC K is about 42mV wheres type C is about 18mV, Type C
> also fits with my approx value of 8mV for 400oC
>
> Back to the original question, i found some datasheets that state a max
> input current of 50mA, so if i size the input resistors correctly and use
> diodes to clamp the input, I think it should be possible to minimise the
> input current and protect the opamp. 6k ohms on each input should limit the
> current to around 5mA assuming a max driving voltage of 30v. I intend to
> use 24V, I see someone has direct connected to a solar panel. that would
> nominally have Voc of 21V.
>
> On Sat, Sep 12, 2020 at 8:45 PM madscientistatlarge <
> [hidden email]> wrote:
>
> > Couldn't find the schematic, but the manual for that iron does have the
> > iron pinout. Normally it has a built in thermistor for temperature sensing
> > (the 5 pin connector has 2 pins for the thermistor, 2 for heater, and one
> > for ground see this <
> > https://runawaybrainz.blogspot.com/2014/08/hakko-fx888d-din-connector-pinouts.html>
> > or the manual. It's possible to only use 2 wires and use the heating
> > element itself as a thermistor, as in the article for Steve Circa I
> > mentioned earlier. I can't find a readable schematic for that station.
> > Sent with ProtonMail Secure Email.
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Saturday, September 12, 2020 5:53 AM, Justin Richards <
> > [hidden email]> wrote:
> >
> > > >
> >
> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> >
> > > That made for an interesting read, some clever designs. I did not know
> > > RTG's used heat this way.
> >
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards
Problem with that measurement is that you have unwanted thermocouples every where wires with different metal connect.  In any case, 32V will absolutely let the smoke out if you are supply the op amp with <30V.  Please send a schematic of your' test setup, or call hako and ask them.  It looks like some use a temperature sensor and read switch in the hande.  A photo of the disassembled handle would really help.


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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 7:49 AM, Justin Richards <[hidden email]> wrote:

> > were a thermocouple the voltage wouldn't drop when the iron heated. I
> > suspect you measured poorly/got interferance picked up. mv signals in that
> > Sent with ProtonMail Secure Email.
>
> It was my intention to state that when heated and measured it starts out
> reading 8mV then drops to around 2mV as it cools.
>
> -----------------------------------------------------------------------------------------------------------------------------
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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
In my opinion it is a superior design as it can be tightly controlled and
recover quicker when soldering. The FX-951 that connects to a FM-2808
handle that supports the T12 tips does not look discontinued, at least
there appears to be no hint on the Hakko site that I could find.

Yes, there are unwanted thermocouples everywhere and I spent some time
eliminating these in a previous design until it became apparent that if
there are an equal number of the same type in each leg then they can
effectively cancel out.

My tests with a CRO seem to indicate that it is relatively noise free,
repeatable and I am using leads that would definitely have many dissimilar
metals making thermocouples and it was this I assumed was the cause of
lower readings relative to a K type until I discovered it is most likely a
C type.

I believe the TS100 and TS80 use a similar design which work very well
according to some reviews.

It may have been a TS100 tip that was x-ray'ed.  Still looking...

On Sat, Sep 12, 2020 at 10:08 PM madscientistatlarge <
[hidden email]> wrote:

> Problem with that measurement is that you have unwanted thermocouples
> every where wires with different metal connect.  In any case, 32V will
> absolutely let the smoke out if you are supply the op amp with <30V.
> Please send a schematic of your' test setup, or call hako and ask them.  It
> looks like some use a temperature sensor and read switch in the hande.  A
> photo of the disassembled handle would really help.
>
>
> Sent with ProtonMail Secure Email.
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Saturday, September 12, 2020 7:49 AM, Justin Richards <
> [hidden email]> wrote:
>
> > > were a thermocouple the voltage wouldn't drop when the iron heated. I
> > > suspect you measured poorly/got interferance picked up. mv signals in
> that
> > > Sent with ProtonMail Secure Email.
> >
> > It was my intention to state that when heated and measured it starts out
> > reading 8mV then drops to around 2mV as it cools.
> >
> >
> -----------------------------------------------------------------------------------------------------------------------------
> >
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
In reply to this post by Justin Richards
Ok, here's the manual for the 951 <https://www.manualslib.com/manual/1388136/Hakko-Electronics-951.html?page=3#manual>  from the specified resistance you no it's some type of RTD, thermocouples usally measure as a low resistance.  The manual says 43-58 ohms for the sensor, which means it's some type of RTD/thermistor.  Also note the sensor has 2 wires that aren't shared.  See the pinout on page 2.  It uses a 5 pin connector, 2 for power, two for sensor, and one for tip ground.  Also the t12 and t15 are the same with the difference being what country they are sold to, it's more marketing scam.


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 7:59 AM, Justin Richards <[hidden email]> wrote:

> We are talking about completely different irons and stations. If you
> google images of the T12 tip you will see that there just isnt the number
> of connections you are suggesting,
>
> In my hakko there is only 2 wires going from the circuit board to the
> plug. If you had a close look of the FX-951 tear down and reverse
> engineering that I originally linked to you would see this. There is no
> measurable connection between the outer cas and the two ring-contacts.
>
> This describes the T12 and indicates the sensor is infact a thermocouple
> http://redlightgreen.org/2019/09/obzor-nabora-vysokokachestvennyh-pajalnyh-zhal-t12/
>
> I had to google snip hunt.
>
> > That resistance is wrong according to the manual which says ohms for the
> > sensor and 2 ohms or less for the heater. Have you connected any of the
> > wires together? If you directly put a power supply across the sensor it
> > was likely damaged. It has a 6 pin plug on it originally, Yes?
> > Thermocouples are very unlikely to share any wire/pin with the heater, it
> > would make the measurement very noisy etc. You could email Hakko and ask
> > them what kind of sensor it is. They apparently have removed the
> > schematics from other websites but are likely willing to tell you what kind
> > of sensor it is and what pins it's normally connected to. The sensor
> > should be between the two blue wires and it likely is a thermocouple, but
> > somethings gone wrong. Again, it's all in the instruction manual.
> > Sent with ProtonMail Secure Email.
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Saturday, September 12, 2020 6:51 AM, Justin Richards <
> > [hidden email]> wrote:
> >
> > > I am reasonably certain these are thermocouples. If I heat it up and
> > > connect it to my multimeter it reads about 8mV and drifts down to about
> > > 2mV. I dont think a thermistor would do that. It reads about 8 ohms when
> > > measuring resistance.
> > > I suspect built into the tip is heating elements that are in series
> > > with the thermocouple and make up each arm of the thermocouple.
> > > There was a x-ray of a soldering iron tip but I am having trouble finding
> > > it.
> > > On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
> > > [hidden email]> wrote:
> > >
> > > > A thermistor is not a thermocouple. You could never put a thermocouple
> > > > across the heating element, thermocouples have very low resistance, it
> > > > would pop like a fuse if you put voltage on it, they are normally
> > > > connected
> > >
> > > > to a very high resistance. Thermocouples produce mV of output, the op
> > > > amp
> > >
> > > > you want to use has a high input offset and high input offset drift, it
> > > > would completely obscure the the actual input voltage.
> > > > I think that station monitors the resistance of the element, after
> > > > briefly
> > >
> > > > disconnecting it from the power supply. Something like this <
> >
> > https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> >
> > > > >
> > > >
> > > > Sent with ProtonMail Secure Email.
> > > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > > On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> > > > [hidden email]> wrote:
> > > >
> > > > > Hi Clint,
> > > > > yes, thermocouples are as you say but with the T12 style soldering
> > > > > tips
> > >
> > > > > the
> > > > > thermocouple is also used as the heating element as strange as that
> > > > > sounds. There are only 2 connections to the tip and it provides both
> > > > > heating and temperature measurement.
> > > > > I am testing on my bench and applying 12v getting it hot then
> > > > > connecting
> > >
> > > > > to
> > > > > the op-amp and reading the output and has survived many cycles. And
> > > > > convinced its a thermocouple as reversing the connections to the op
> > > > > amp
> > >
> > > > > has
> > > > > the expected outcome. I am so tempted to connect the 12v while
> > > > > connected
> > >
> > > > > to the opamp ( I found a spare) as it is protected by the 2 x 1k ohm
> > > > > input
> > > > > resistors but I will heed your advice.
> > > > > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed
> > > > > engineered
> > >
> > > > > the
> > > > > same station I have. On closer inspection I don't see the disconnect
> > > > > when
> > >
> > > > > heating. I was sure that schematic had a disconnect transistor to
> > > > > protect
> > >
> > > > > the opamp, I will have to watch again.
> > > > > That station is ok, except I want a web page to tweak all the PID
> > > > > constants
> > > > > and a rotary encoder with OLED display for fast temperature
> > > > > adjustment.
> > >
> > > > > It
> > > > > currently has a weird insert card and clunky non-intuitive buttons
> > > > > for
> > >
> > > > > temp
> > > > > adjust.
> > > > > All is tested ok, my code supports MAX6675, DHT, thermistors and
> > > > > 4diodes
> > >
> > > > > in
> > > > > series and is used at home to make black garlic where the humidity is
> > > > > maintained with a peristaltic pump etc among other things
> > > > > A very early version can be seen here
> >
> > https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> >
> > > > > I now want to leverage of all that development and control a
> > > > > soldering
> > >
> > > > > iron
> > > > > the way I want it. Fast heating, setable standby temp, easy adjust,
> > > > > just
> > >
> > > > > need to do the last bit.
> > > > > Cheers Justin
> > > > > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email] wrote:
> > > > >
> > > > > > I think perhaps you've got a few misconceptions here.
> > > > > > Thermocouple usually refers to a dissimilar metal junction sensor,
> > > > > > applying
> > > > >
> > > > > > heat to it creates a voltage across the two wire ends*, you don't
> > > > > > feed
> > >
> > > > > > power to a thermocouple.
> > > > > > Most chip datasheets specify the maximum input voltage in relation
> > > > > > to
> > >
> > > > > > VCC,
> > > > >
> > > > > > your GL358 (if I'm reading the datasheet right) will be able to
> > > > > > cope
> > >
> > > > > > with
> > > > >
> > > > > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or -1.5V,
> > > > > > 32V
> > >
> > > > > > will
> > > > >
> > > > > > probably release the magic smoke.
> > > > > > *Thermocouples are really useful, put enough of them in series and
> > > > > > apply
> > > > >
> > > > > > fire, you can charge a car battery!!!
> >
> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> >
> > > > > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> > > > > > [hidden email]
> > > > >
> > > > > > wrote:
> > > > > >
> > > > > > > Experimenting with using a ESP8266 as a soldering iron PID
> > > > > > > controller
> > >
> > > > > > > driving the ADC with the output of an opamp.
> > > > > > > The GL358 opamp datasheet specifies max differential input
> > > > > > > voltage as
> > >
> > > > > > > 32V.
> > > > > > > I would like to know if that is as it sounds and I can force the
> > > > > > > inputs
> > > > >
> > > > > > > to
> > > > > > > have a max of 32v across them with a single supply to the Opamp
> > > > > > > of
> > >
> > > > > > > +5V.
> > > > >
> > > > > > > I
> > > > > > > am still learning about opamps and thought the inputs were to be
> > > > > > > considered
> > > > > > > as a virtual ground and they will effectively be at the same
> > > > > > > potential
> > > > >
> > > > > > > but
> > > > > > > here i would be brute forcing a voltage across them and
> > > > > > > concerned it
> > >
> > > > > > > may
> > > > >
> > > > > > > be
> > > > > > > damaging and bad practice.
> > > > > > > The GL358 (was in the junk box) is configured as a dual amp to
> > > > > > > amplify
> > > > >
> > > > > > > the
> > > > > > > thermocouple (integral part of soldering tip) output of approx
> > > > > > > 2mV -
> > >
> > > > > > > 8mV
> > > > >
> > > > > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > > > > One side of the thermocouple is grounded and connected via a
> > > > > > > resistor to
> > > > >
> > > > > > > the inverting input while the other side is connected via another
> > > > > > > resistor to the non-inverting input.
> > > > > > > I plan to measure temperature then apply 24V across the
> > > > > > > thermocouple.
> > >
> > > > > > > which
> > > > > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > > > > As a caution I plan to have back to back diodes at the inputs to
> > > > > > > limit
> > > > >
> > > > > > > the
> > > > > > > voltage across them to approx 0.7v.
> > > > > > > But back to the original question, are the protection diodes
> > > > > > > needed
> > >
> > > > > > > given a
> > > > > > > maximum differential voltage of 32 volts or is that only if the
> > > > > > > supply is
> > > > >
> > > > > > > also at 32V.
> > > > > > > I found a design that disconnects the thermocouple from the opamp
> > > > > > > during
> > > > >
> > > > > > > heating but not sure if that is actually required and obviously
> > > > > > > simplifies
> > > > > > > the design if not.
> > > > > > > Regards
> > > > > > > Justin
> > > > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > > > View/change your membership options at
> > > > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > > > >
> > > > > > --
> > > > > > Clint. M0UAW IO83
> > > > > > No trees were harmed in the sending of this mail. However, a large
> > > > > > number
> > > > >
> > > > > > of electrons were greatly inconvenienced.
> > > >
> > > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > > View/change your membership options at
> > > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > > >
> > > > > --
> > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > > View/change your membership options at
> > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > >
> > > > --
> > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > > View/change your membership options at
> > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
> > > --
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> >
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist



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Re: [EE]: OpAmp Max differential input voltage GL358

Justin Richards
Thanks for the link but that is the 951 952 soldering gun.  A completely
different beast from the FX-951 soldering station that connects to an
FM2025 handle.that uses T12 tips.

Mine is more like
https://doc.hakko.com/download.php?_gs=on&l=en&kp=fx+951&d=401 and
indicates the heater and sensor resistance should be 8 ohms which is what I
get.  It is only taken from two point as shown in the diagram.

Thanks for all your input




On Sat, Sep 12, 2020 at 10:37 PM madscientistatlarge <
[hidden email]> wrote:

> Ok, here's the manual for the 951 <
> https://www.manualslib.com/manual/1388136/Hakko-Electronics-951.html?page=3#manual>
> from the specified resistance you no it's some type of RTD, thermocouples
> usally measure as a low resistance.  The manual says 43-58 ohms for the
> sensor, which means it's some type of RTD/thermistor.  Also note the sensor
> has 2 wires that aren't shared.  See the pinout on page 2.  It uses a 5 pin
> connector, 2 for power, two for sensor, and one for tip ground.  Also the
> t12 and t15 are the same with the difference being what country they are
> sold to, it's more marketing scam.
>
>
> Sent with ProtonMail Secure Email.
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Saturday, September 12, 2020 7:59 AM, Justin Richards <
> [hidden email]> wrote:
>
> > We are talking about completely different irons and stations. If you
> > google images of the T12 tip you will see that there just isnt the number
> > of connections you are suggesting,
> >
> > In my hakko there is only 2 wires going from the circuit board to the
> > plug. If you had a close look of the FX-951 tear down and reverse
> > engineering that I originally linked to you would see this. There is no
> > measurable connection between the outer cas and the two ring-contacts.
> >
> > This describes the T12 and indicates the sensor is infact a thermocouple
> >
> http://redlightgreen.org/2019/09/obzor-nabora-vysokokachestvennyh-pajalnyh-zhal-t12/
> >
> > I had to google snip hunt.
> >
> > > That resistance is wrong according to the manual which says ohms for
> the
> > > sensor and 2 ohms or less for the heater. Have you connected any of the
> > > wires together? If you directly put a power supply across the sensor it
> > > was likely damaged. It has a 6 pin plug on it originally, Yes?
> > > Thermocouples are very unlikely to share any wire/pin with the heater,
> it
> > > would make the measurement very noisy etc. You could email Hakko and
> ask
> > > them what kind of sensor it is. They apparently have removed the
> > > schematics from other websites but are likely willing to tell you what
> kind
> > > of sensor it is and what pins it's normally connected to. The sensor
> > > should be between the two blue wires and it likely is a thermocouple,
> but
> > > somethings gone wrong. Again, it's all in the instruction manual.
> > > Sent with ProtonMail Secure Email.
> > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > On Saturday, September 12, 2020 6:51 AM, Justin Richards <
> > > [hidden email]> wrote:
> > >
> > > > I am reasonably certain these are thermocouples. If I heat it up and
> > > > connect it to my multimeter it reads about 8mV and drifts down to
> about
> > > > 2mV. I dont think a thermistor would do that. It reads about 8 ohms
> when
> > > > measuring resistance.
> > > > I suspect built into the tip is heating elements that are in series
> > > > with the thermocouple and make up each arm of the thermocouple.
> > > > There was a x-ray of a soldering iron tip but I am having trouble
> finding
> > > > it.
> > > > On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
> > > > [hidden email]> wrote:
> > > >
> > > > > A thermistor is not a thermocouple. You could never put a
> thermocouple
> > > > > across the heating element, thermocouples have very low
> resistance, it
> > > > > would pop like a fuse if you put voltage on it, they are normally
> > > > > connected
> > > >
> > > > > to a very high resistance. Thermocouples produce mV of output, the
> op
> > > > > amp
> > > >
> > > > > you want to use has a high input offset and high input offset
> drift, it
> > > > > would completely obscure the the actual input voltage.
> > > > > I think that station monitors the resistance of the element, after
> > > > > briefly
> > > >
> > > > > disconnecting it from the power supply. Something like this <
> > >
> > >
> https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> > >
> > > > > >
> > > > >
> > > > > Sent with ProtonMail Secure Email.
> > > > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > > > On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> > > > > [hidden email]> wrote:
> > > > >
> > > > > > Hi Clint,
> > > > > > yes, thermocouples are as you say but with the T12 style
> soldering
> > > > > > tips
> > > >
> > > > > > the
> > > > > > thermocouple is also used as the heating element as strange as
> that
> > > > > > sounds. There are only 2 connections to the tip and it provides
> both
> > > > > > heating and temperature measurement.
> > > > > > I am testing on my bench and applying 12v getting it hot then
> > > > > > connecting
> > > >
> > > > > > to
> > > > > > the op-amp and reading the output and has survived many cycles.
> And
> > > > > > convinced its a thermocouple as reversing the connections to the
> op
> > > > > > amp
> > > >
> > > > > > has
> > > > > > the expected outcome. I am so tempted to connect the 12v while
> > > > > > connected
> > > >
> > > > > > to the opamp ( I found a spare) as it is protected by the 2 x 1k
> ohm
> > > > > > input
> > > > > > resistors but I will heed your advice.
> > > > > > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed
> > > > > > engineered
> > > >
> > > > > > the
> > > > > > same station I have. On closer inspection I don't see the
> disconnect
> > > > > > when
> > > >
> > > > > > heating. I was sure that schematic had a disconnect transistor to
> > > > > > protect
> > > >
> > > > > > the opamp, I will have to watch again.
> > > > > > That station is ok, except I want a web page to tweak all the PID
> > > > > > constants
> > > > > > and a rotary encoder with OLED display for fast temperature
> > > > > > adjustment.
> > > >
> > > > > > It
> > > > > > currently has a weird insert card and clunky non-intuitive
> buttons
> > > > > > for
> > > >
> > > > > > temp
> > > > > > adjust.
> > > > > > All is tested ok, my code supports MAX6675, DHT, thermistors and
> > > > > > 4diodes
> > > >
> > > > > > in
> > > > > > series and is used at home to make black garlic where the
> humidity is
> > > > > > maintained with a peristaltic pump etc among other things
> > > > > > A very early version can be seen here
> > >
> > >
> https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> > >
> > > > > > I now want to leverage of all that development and control a
> > > > > > soldering
> > > >
> > > > > > iron
> > > > > > the way I want it. Fast heating, setable standby temp, easy
> adjust,
> > > > > > just
> > > >
> > > > > > need to do the last bit.
> > > > > > Cheers Justin
> > > > > > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email]
> wrote:
> > > > > >
> > > > > > > I think perhaps you've got a few misconceptions here.
> > > > > > > Thermocouple usually refers to a dissimilar metal junction
> sensor,
> > > > > > > applying
> > > > > >
> > > > > > > heat to it creates a voltage across the two wire ends*, you
> don't
> > > > > > > feed
> > > >
> > > > > > > power to a thermocouple.
> > > > > > > Most chip datasheets specify the maximum input voltage in
> relation
> > > > > > > to
> > > >
> > > > > > > VCC,
> > > > > >
> > > > > > > your GL358 (if I'm reading the datasheet right) will be able to
> > > > > > > cope
> > > >
> > > > > > > with
> > > > > >
> > > > > > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or
> -1.5V,
> > > > > > > 32V
> > > >
> > > > > > > will
> > > > > >
> > > > > > > probably release the magic smoke.
> > > > > > > *Thermocouples are really useful, put enough of them in series
> and
> > > > > > > apply
> > > > > >
> > > > > > > fire, you can charge a car battery!!!
> > >
> > >
> http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> > >
> > > > > > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> > > > > > > [hidden email]
> > > > > >
> > > > > > > wrote:
> > > > > > >
> > > > > > > > Experimenting with using a ESP8266 as a soldering iron PID
> > > > > > > > controller
> > > >
> > > > > > > > driving the ADC with the output of an opamp.
> > > > > > > > The GL358 opamp datasheet specifies max differential input
> > > > > > > > voltage as
> > > >
> > > > > > > > 32V.
> > > > > > > > I would like to know if that is as it sounds and I can force
> the
> > > > > > > > inputs
> > > > > >
> > > > > > > > to
> > > > > > > > have a max of 32v across them with a single supply to the
> Opamp
> > > > > > > > of
> > > >
> > > > > > > > +5V.
> > > > > >
> > > > > > > > I
> > > > > > > > am still learning about opamps and thought the inputs were
> to be
> > > > > > > > considered
> > > > > > > > as a virtual ground and they will effectively be at the same
> > > > > > > > potential
> > > > > >
> > > > > > > > but
> > > > > > > > here i would be brute forcing a voltage across them and
> > > > > > > > concerned it
> > > >
> > > > > > > > may
> > > > > >
> > > > > > > > be
> > > > > > > > damaging and bad practice.
> > > > > > > > The GL358 (was in the junk box) is configured as a dual amp
> to
> > > > > > > > amplify
> > > > > >
> > > > > > > > the
> > > > > > > > thermocouple (integral part of soldering tip) output of
> approx
> > > > > > > > 2mV -
> > > >
> > > > > > > > 8mV
> > > > > >
> > > > > > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > > > > > One side of the thermocouple is grounded and connected via a
> > > > > > > > resistor to
> > > > > >
> > > > > > > > the inverting input while the other side is connected via
> another
> > > > > > > > resistor to the non-inverting input.
> > > > > > > > I plan to measure temperature then apply 24V across the
> > > > > > > > thermocouple.
> > > >
> > > > > > > > which
> > > > > > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > > > > > As a caution I plan to have back to back diodes at the
> inputs to
> > > > > > > > limit
> > > > > >
> > > > > > > > the
> > > > > > > > voltage across them to approx 0.7v.
> > > > > > > > But back to the original question, are the protection diodes
> > > > > > > > needed
> > > >
> > > > > > > > given a
> > > > > > > > maximum differential voltage of 32 volts or is that only if
> the
> > > > > > > > supply is
> > > > > >
> > > > > > > > also at 32V.
> > > > > > > > I found a design that disconnects the thermocouple from the
> opamp
> > > > > > > > during
> > > > > >
> > > > > > > > heating but not sure if that is actually required and
> obviously
> > > > > > > > simplifies
> > > > > > > > the design if not.
> > > > > > > > Regards
> > > > > > > > Justin
> > > > > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list
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Re: [EE]: OpAmp Max differential input voltage GL358

madscientistatlarge
Here's the service manual, still no schematic which is just silly.  These are expensive and not hard to reverse engineer.  I've found most things aren't that hard to reverse engineer, especially something so simple.  The software may be protected, but that's pretty easy to emulate as well.


Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, September 12, 2020 8:59 AM, Justin Richards <[hidden email]> wrote:

> Thanks for the link but that is the 951 952 soldering gun. A completely
> different beast from the FX-951 soldering station that connects to an
> FM2025 handle.that uses T12 tips.
>
> Mine is more like
> https://doc.hakko.com/download.php?_gs=on&l=en&kp=fx+951&d=401 and
> indicates the heater and sensor resistance should be 8 ohms which is what I
> get. It is only taken from two point as shown in the diagram.
>
> Thanks for all your input
>
> On Sat, Sep 12, 2020 at 10:37 PM madscientistatlarge <
> [hidden email]> wrote:
>
> > Ok, here's the manual for the 951 <
> > https://www.manualslib.com/manual/1388136/Hakko-Electronics-951.html?page=3#manual>
> > from the specified resistance you no it's some type of RTD, thermocouples
> > usally measure as a low resistance. The manual says 43-58 ohms for the
> > sensor, which means it's some type of RTD/thermistor. Also note the sensor
> > has 2 wires that aren't shared. See the pinout on page 2. It uses a 5 pin
> > connector, 2 for power, two for sensor, and one for tip ground. Also the
> > t12 and t15 are the same with the difference being what country they are
> > sold to, it's more marketing scam.
> > Sent with ProtonMail Secure Email.
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Saturday, September 12, 2020 7:59 AM, Justin Richards <
> > [hidden email]> wrote:
> >
> > > We are talking about completely different irons and stations. If you
> > > google images of the T12 tip you will see that there just isnt the number
> > > of connections you are suggesting,
> > > In my hakko there is only 2 wires going from the circuit board to the
> > > plug. If you had a close look of the FX-951 tear down and reverse
> > > engineering that I originally linked to you would see this. There is no
> > > measurable connection between the outer cas and the two ring-contacts.
> > > This describes the T12 and indicates the sensor is infact a thermocouple
> >
> > http://redlightgreen.org/2019/09/obzor-nabora-vysokokachestvennyh-pajalnyh-zhal-t12/
> >
> > > I had to google snip hunt.
> > >
> > > > That resistance is wrong according to the manual which says ohms for
> > > > the
> > >
> > > > sensor and 2 ohms or less for the heater. Have you connected any of the
> > > > wires together? If you directly put a power supply across the sensor it
> > > > was likely damaged. It has a 6 pin plug on it originally, Yes?
> > > > Thermocouples are very unlikely to share any wire/pin with the heater,
> > > > it
> > >
> > > > would make the measurement very noisy etc. You could email Hakko and
> > > > ask
> > >
> > > > them what kind of sensor it is. They apparently have removed the
> > > > schematics from other websites but are likely willing to tell you what
> > > > kind
> > >
> > > > of sensor it is and what pins it's normally connected to. The sensor
> > > > should be between the two blue wires and it likely is a thermocouple,
> > > > but
> > >
> > > > somethings gone wrong. Again, it's all in the instruction manual.
> > > > Sent with ProtonMail Secure Email.
> > > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > > On Saturday, September 12, 2020 6:51 AM, Justin Richards <
> > > > [hidden email]> wrote:
> > > >
> > > > > I am reasonably certain these are thermocouples. If I heat it up and
> > > > > connect it to my multimeter it reads about 8mV and drifts down to
> > > > > about
> > >
> > > > > 2mV. I dont think a thermistor would do that. It reads about 8 ohms
> > > > > when
> > >
> > > > > measuring resistance.
> > > > > I suspect built into the tip is heating elements that are in series
> > > > > with the thermocouple and make up each arm of the thermocouple.
> > > > > There was a x-ray of a soldering iron tip but I am having trouble
> > > > > finding
> > >
> > > > > it.
> > > > > On Sat, Sep 12, 2020 at 8:11 PM madscientistatlarge <
> > > > > [hidden email]> wrote:
> > > > >
> > > > > > A thermistor is not a thermocouple. You could never put a
> > > > > > thermocouple
> > >
> > > > > > across the heating element, thermocouples have very low
> > > > > > resistance, it
> > >
> > > > > > would pop like a fuse if you put voltage on it, they are normally
> > > > > > connected
> > > > >
> > > > > > to a very high resistance. Thermocouples produce mV of output, the
> > > > > > op
> > >
> > > > > > amp
> > > > >
> > > > > > you want to use has a high input offset and high input offset
> > > > > > drift, it
> > >
> > > > > > would completely obscure the the actual input voltage.
> > > > > > I think that station monitors the resistance of the element, after
> > > > > > briefly
> > > > >
> > > > > > disconnecting it from the power supply. Something like this <
> >
> > https://circuitcellar.com/resources/ee-tips/how-to-measure-temperature-with-a-soldering-iron/
> >
> > > > > > >
> > > > > >
> > > > > > Sent with ProtonMail Secure Email.
> > > > > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > > > > On Saturday, September 12, 2020 5:12 AM, Justin Richards <
> > > > > > [hidden email]> wrote:
> > > > > >
> > > > > > > Hi Clint,
> > > > > > > yes, thermocouples are as you say but with the T12 style
> > > > > > > soldering
> > >
> > > > > > > tips
> > > > >
> > > > > > > the
> > > > > > > thermocouple is also used as the heating element as strange as
> > > > > > > that
> > >
> > > > > > > sounds. There are only 2 connections to the tip and it provides
> > > > > > > both
> > >
> > > > > > > heating and temperature measurement.
> > > > > > > I am testing on my bench and applying 12v getting it hot then
> > > > > > > connecting
> > > > >
> > > > > > > to
> > > > > > > the op-amp and reading the output and has survived many cycles.
> > > > > > > And
> > >
> > > > > > > convinced its a thermocouple as reversing the connections to the
> > > > > > > op
> > >
> > > > > > > amp
> > > > >
> > > > > > > has
> > > > > > > the expected outcome. I am so tempted to connect the 12v while
> > > > > > > connected
> > > > >
> > > > > > > to the opamp ( I found a spare) as it is protected by the 2 x 1k
> > > > > > > ohm
> > >
> > > > > > > input
> > > > > > > resistors but I will heed your advice.
> > > > > > > This chap https://youtu.be/vudfIq6PQMw?t=1290 has reversed
> > > > > > > engineered
> > > > >
> > > > > > > the
> > > > > > > same station I have. On closer inspection I don't see the
> > > > > > > disconnect
> > >
> > > > > > > when
> > > > >
> > > > > > > heating. I was sure that schematic had a disconnect transistor to
> > > > > > > protect
> > > > >
> > > > > > > the opamp, I will have to watch again.
> > > > > > > That station is ok, except I want a web page to tweak all the PID
> > > > > > > constants
> > > > > > > and a rotary encoder with OLED display for fast temperature
> > > > > > > adjustment.
> > > > >
> > > > > > > It
> > > > > > > currently has a weird insert card and clunky non-intuitive
> > > > > > > buttons
> > >
> > > > > > > for
> > > > >
> > > > > > > temp
> > > > > > > adjust.
> > > > > > > All is tested ok, my code supports MAX6675, DHT, thermistors and
> > > > > > > 4diodes
> > > > >
> > > > > > > in
> > > > > > > series and is used at home to make black garlic where the
> > > > > > > humidity is
> > >
> > > > > > > maintained with a peristaltic pump etc among other things
> > > > > > > A very early version can be seen here
> >
> > https://hackaday.io/project/167840-slowcooker-esp8266-based-pid-controller
> >
> > > > > > > I now want to leverage of all that development and control a
> > > > > > > soldering
> > > > >
> > > > > > > iron
> > > > > > > the way I want it. Fast heating, setable standby temp, easy
> > > > > > > adjust,
> > >
> > > > > > > just
> > > > >
> > > > > > > need to do the last bit.
> > > > > > > Cheers Justin
> > > > > > > On Sat, Sep 12, 2020 at 5:29 PM Clint Jay [hidden email]
> > > > > > > wrote:
> > >
> > > > > > > > I think perhaps you've got a few misconceptions here.
> > > > > > > > Thermocouple usually refers to a dissimilar metal junction
> > > > > > > > sensor,
> > >
> > > > > > > > applying
> > > > > > >
> > > > > > > > heat to it creates a voltage across the two wire ends*, you
> > > > > > > > don't
> > >
> > > > > > > > feed
> > > > >
> > > > > > > > power to a thermocouple.
> > > > > > > > Most chip datasheets specify the maximum input voltage in
> > > > > > > > relation
> > >
> > > > > > > > to
> > > > >
> > > > > > > > VCC,
> > > > > > >
> > > > > > > > your GL358 (if I'm reading the datasheet right) will be able to
> > > > > > > > cope
> > > > >
> > > > > > > > with
> > > > > > >
> > > > > > > > VCC +/-1.5V, so for 5V VCC you could safely input +6.5V or
> > > > > > > > -1.5V,
> > >
> > > > > > > > 32V
> > > > >
> > > > > > > > will
> > > > > > >
> > > > > > > > probably release the magic smoke.
> > > > > > > > *Thermocouples are really useful, put enough of them in series
> > > > > > > > and
> > >
> > > > > > > > apply
> > > > > > >
> > > > > > > > fire, you can charge a car battery!!!
> >
> > http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#g
> >
> > > > > > > > On Sat, 12 Sep 2020 at 10:00, Justin Richards
> > > > > > > > [hidden email]
> > > > > > >
> > > > > > > > wrote:
> > > > > > > >
> > > > > > > > > Experimenting with using a ESP8266 as a soldering iron PID
> > > > > > > > > controller
> > > > >
> > > > > > > > > driving the ADC with the output of an opamp.
> > > > > > > > > The GL358 opamp datasheet specifies max differential input
> > > > > > > > > voltage as
> > > > >
> > > > > > > > > 32V.
> > > > > > > > > I would like to know if that is as it sounds and I can force
> > > > > > > > > the
> > >
> > > > > > > > > inputs
> > > > > > >
> > > > > > > > > to
> > > > > > > > > have a max of 32v across them with a single supply to the
> > > > > > > > > Opamp
> > >
> > > > > > > > > of
> > > > >
> > > > > > > > > +5V.
> > > > > > >
> > > > > > > > > I
> > > > > > > > > am still learning about opamps and thought the inputs were
> > > > > > > > > to be
> > >
> > > > > > > > > considered
> > > > > > > > > as a virtual ground and they will effectively be at the same
> > > > > > > > > potential
> > > > > > >
> > > > > > > > > but
> > > > > > > > > here i would be brute forcing a voltage across them and
> > > > > > > > > concerned it
> > > > >
> > > > > > > > > may
> > > > > > >
> > > > > > > > > be
> > > > > > > > > damaging and bad practice.
> > > > > > > > > The GL358 (was in the junk box) is configured as a dual amp
> > > > > > > > > to
> > >
> > > > > > > > > amplify
> > > > > > >
> > > > > > > > > the
> > > > > > > > > thermocouple (integral part of soldering tip) output of
> > > > > > > > > approx
> > >
> > > > > > > > > 2mV -
> > > > >
> > > > > > > > > 8mV
> > > > > > >
> > > > > > > > > (~30oC - 400oC) .to approx 40mV - 1500mV.
> > > > > > > > > One side of the thermocouple is grounded and connected via a
> > > > > > > > > resistor to
> > > > > > >
> > > > > > > > > the inverting input while the other side is connected via
> > > > > > > > > another
> > >
> > > > > > > > > resistor to the non-inverting input.
> > > > > > > > > I plan to measure temperature then apply 24V across the
> > > > > > > > > thermocouple.
> > > > >
> > > > > > > > > which
> > > > > > > > > will drive 24V across the two 1k ohm opamp input resistors.
> > > > > > > > > As a caution I plan to have back to back diodes at the
> > > > > > > > > inputs to
> > >
> > > > > > > > > limit
> > > > > > >
> > > > > > > > > the
> > > > > > > > > voltage across them to approx 0.7v.
> > > > > > > > > But back to the original question, are the protection diodes
> > > > > > > > > needed
> > > > >
> > > > > > > > > given a
> > > > > > > > > maximum differential voltage of 32 volts or is that only if
> > > > > > > > > the
> > >
> > > > > > > > > supply is
> > > > > > >
> > > > > > > > > also at 32V.
> > > > > > > > > I found a design that disconnects the thermocouple from the
> > > > > > > > > opamp
> > >
> > > > > > > > > during
> > > > > > >
> > > > > > > > > heating but not sure if that is actually required and
> > > > > > > > > obviously
> > >
> > > > > > > > > simplifies
> > > > > > > > > the design if not.
> > > > > > > > > Regards
> > > > > > > > > Justin
> > > > > > > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list
> > > > > > > > > archive
> > >
> > > > > > > > > View/change your membership options at
> > > > > > > > > http://mailman.mit.edu/mailman/listinfo/piclist
> > > > > > > >
> > > > > > > > --
> > > > > > > > Clint. M0UAW IO83
> > > > > > > > No trees were harmed in the sending of this mail. However, a
> > > > > > > > large
> > >
> > > > > > > > number
> > > > > > >
> > > > > > > > of electrons were greatly inconvenienced.
> > > > > >
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