[EE] Detecting a change of level on four lines with digital logic/analog circuitry?

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[EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Jason White-20
Hi everyone,

I have an application where I need to generate at pulse least 1 microsecond
long any time a rising or falling edge is detected on four digital lines.
The four signals can change at any time to any direction. The pulse is used
to trigger a timer providing a reset signal to the rest of the system.
Microcontrollers and programmable logic devices aren't allowed.

Four 74HC123s will do it, but are too big.
Four window comparators monitoring the signal through an RC will do it, but
also seems too big.

Is four schmitt trigger XOR gates with four RC's the smallest
implementation?

I was thinking some sort of analog implementation might be able to do it
smaller. But AC coupling the four signals together would allow them to
cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
better?

Regards,
Jason White
--
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Brent Brown-2
Hi Jason,

How about: Sum the lines with 4 x resistors, feed this analog voltage into the +ve
input of one comparator, and -ve input of another comparator. Remaining inputs to
a C, with R to analog voltage above, where RC time constant sets pulse period.
Combine comparator outputs with 2 x diodes and a pull-up or pull-down resistor as
required.

Brent.

On 4 Jun 2020 at 16:35, Jason White wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microsecond
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is used
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, but
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?


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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

David C Brown
In reply to this post by Jason White-20
How much latency is acceptable.  And is the output pulse retriggerable.

Would using an 8 pin PIC to sample and digitally compare the inputs be too
slow?
With a 32MHz part you would be able  to keep the latency under a micro
second.
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: 01663 733236
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Thu, 4 Jun 2020 at 21:38, Jason White <[hidden email]>
wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microsecond
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is used
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, but
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?
>
> Regards,
> Jason White
> --
> 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] Detecting a change of level on four lines with digital logic/analog circuitry?

James Burkart-2
In reply to this post by Jason White-20
I'm curious. Why not microcontrollers?
--
Sincerely,

James Burkart
*925.667.7175*


On Thu, Jun 4, 2020 at 2:37 PM Jason White <
[hidden email]> wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microsecond
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is used
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, but
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?
>
> Regards,
> Jason White
> --
> 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
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Justin Richards
In reply to this post by Jason White-20
Base on "The four signals can change at any time to any direction " then I
must assume that 2 or more lines may transition at precisley the same time.

Is that a correct assumption.

Justin

On Fri, Jun 5, 2020 at 4:38 AM Jason White <
[hidden email]> wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microsecond
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is used
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, but
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?
>
> Regards,
> Jason White
> --
> 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
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Forrest Christian (List Account)
In reply to this post by Jason White-20
It's too bad that programmable devices are not permitted...   This is
perfect for an edge trigger on a microcontroller, or a tiny programmable
logic device.   I would argue that using the functions available on a
modern programmable device is going to be at least as reliable as any
discrete logic/component solution.

But...

Take four xor gates (1 single 74hc86) each wired as a 'edge to glitch'
converter - that is, wire each line directly to one input pin and through a
rc filter to the other input pin.  This has the effect of slightly delaying
the input to the second input pin, creating a situation where you get a
brief pulse on the output on each edge as it catches up with the
non-delayed first pin.

You can then insert a diode into the output line, creating a 'wired or' for
the output, so if *any* of the units have an edge, you get a pulse.
 Direction of diode and whether you need a pullup/pulldown resistor is left
as an exercise to the reader.

Once you have that pulse, feel free to use an HC123 or a 555 to stretch it
out.

Or you could just try to convince whoever made the 'no programmable
devices' policy that something like a PIC16F15313 which can be factory
programmed by microchip is smaller, cheaper, and is just as reliable.
Plus, it is highly likely that the entire function you describe can be done
in one of the inbuilt "core independent peripherals" which wouldn't even
require the core to be running, and the latency if done right wouldn't be
any more than the discrete solution.  Or you can save a few cents if you
can tolerate a bit of interrupt latency.  Of course, I can understand that
sometimes in an application the 'black box' nature of a programmable device
isn't really possible to use.  But those applications are typically the
type where you're going to have to qualify everything.

On Thu, Jun 4, 2020 at 2:47 PM Jason White <
[hidden email]> wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microsecond
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is used
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, but
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?
>
> Regards,
> Jason White
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


--
- Forrest
--
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

David C Brown
Sorry.  I initially missed the "use last century's technology" caveat.

Using RC filters for digital delays is bad practice since, the output is a
slow edge which should be read by a Schmitt  gate.
However you can get the same effect by using  a slow gate for the delay.
Actually, four inverters take up less real estate than four resistors and
four caps.  Or if the old technology only rule precludes SMT about the same

If you use a 555 for the output monostable you are looking at the
equivalent of four 16 pin DIPs of real estate
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: 01663 733236
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Fri, 5 Jun 2020 at 09:15, Forrest Christian (List Account) <
[hidden email]> wrote:

> It's too bad that programmable devices are not permitted...   This is
> perfect for an edge trigger on a microcontroller, or a tiny programmable
> logic device.   I would argue that using the functions available on a
> modern programmable device is going to be at least as reliable as any
> discrete logic/component solution.
>
> But...
>
> Take four xor gates (1 single 74hc86) each wired as a 'edge to glitch'
> converter - that is, wire each line directly to one input pin and through a
> rc filter to the other input pin.  This has the effect of slightly delaying
> the input to the second input pin, creating a situation where you get a
> brief pulse on the output on each edge as it catches up with the
> non-delayed first pin.
>
> You can then insert a diode into the output line, creating a 'wired or' for
> the output, so if *any* of the units have an edge, you get a pulse.
>  Direction of diode and whether you need a pullup/pulldown resistor is left
> as an exercise to the reader.
>
> Once you have that pulse, feel free to use an HC123 or a 555 to stretch it
> out.
>
> Or you could just try to convince whoever made the 'no programmable
> devices' policy that something like a PIC16F15313 which can be factory
> programmed by microchip is smaller, cheaper, and is just as reliable.
> Plus, it is highly likely that the entire function you describe can be done
> in one of the inbuilt "core independent peripherals" which wouldn't even
> require the core to be running, and the latency if done right wouldn't be
> any more than the discrete solution.  Or you can save a few cents if you
> can tolerate a bit of interrupt latency.  Of course, I can understand that
> sometimes in an application the 'black box' nature of a programmable device
> isn't really possible to use.  But those applications are typically the
> type where you're going to have to qualify everything.
>
> On Thu, Jun 4, 2020 at 2:47 PM Jason White <
> [hidden email]> wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital lines.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do it
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
> >
> > Regards,
> > Jason White
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> - Forrest
> --
> 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
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Forrest Christian (List Account)
I was making the assumption that one would choose a RC time constant which
would meet the rise/fall time qualifications.   You don't need much delay.

On the other hand, adding some slow gates works too...

On Fri, Jun 5, 2020 at 3:12 AM David C Brown <[hidden email]> wrote:

> Sorry.  I initially missed the "use last century's technology" caveat.
>
> Using RC filters for digital delays is bad practice since, the output is a
> slow edge which should be read by a Schmitt  gate.
> However you can get the same effect by using  a slow gate for the delay.
> Actually, four inverters take up less real estate than four resistors and
> four caps.  Or if the old technology only rule precludes SMT about the same
>
> If you use a 555 for the output monostable you are looking at the
> equivalent of four 16 pin DIPs of real estate
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak                           Phone: 01663 733236
> Derbyshire                eMail: [hidden email]
> SK23 7ND          web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>
>
>
> *Sent from my etch-a-sketch*
>
>
> On Fri, 5 Jun 2020 at 09:15, Forrest Christian (List Account) <
> [hidden email]> wrote:
>
> > It's too bad that programmable devices are not permitted...   This is
> > perfect for an edge trigger on a microcontroller, or a tiny programmable
> > logic device.   I would argue that using the functions available on a
> > modern programmable device is going to be at least as reliable as any
> > discrete logic/component solution.
> >
> > But...
> >
> > Take four xor gates (1 single 74hc86) each wired as a 'edge to glitch'
> > converter - that is, wire each line directly to one input pin and
> through a
> > rc filter to the other input pin.  This has the effect of slightly
> delaying
> > the input to the second input pin, creating a situation where you get a
> > brief pulse on the output on each edge as it catches up with the
> > non-delayed first pin.
> >
> > You can then insert a diode into the output line, creating a 'wired or'
> for
> > the output, so if *any* of the units have an edge, you get a pulse.
> >  Direction of diode and whether you need a pullup/pulldown resistor is
> left
> > as an exercise to the reader.
> >
> > Once you have that pulse, feel free to use an HC123 or a 555 to stretch
> it
> > out.
> >
> > Or you could just try to convince whoever made the 'no programmable
> > devices' policy that something like a PIC16F15313 which can be factory
> > programmed by microchip is smaller, cheaper, and is just as reliable.
> > Plus, it is highly likely that the entire function you describe can be
> done
> > in one of the inbuilt "core independent peripherals" which wouldn't even
> > require the core to be running, and the latency if done right wouldn't be
> > any more than the discrete solution.  Or you can save a few cents if you
> > can tolerate a bit of interrupt latency.  Of course, I can understand
> that
> > sometimes in an application the 'black box' nature of a programmable
> device
> > isn't really possible to use.  But those applications are typically the
> > type where you're going to have to qualify everything.
> >
> > On Thu, Jun 4, 2020 at 2:47 PM Jason White <
> > [hidden email]> wrote:
> >
> > > Hi everyone,
> > >
> > > I have an application where I need to generate at pulse least 1
> > microsecond
> > > long any time a rising or falling edge is detected on four digital
> lines.
> > > The four signals can change at any time to any direction. The pulse is
> > used
> > > to trigger a timer providing a reset signal to the rest of the system.
> > > Microcontrollers and programmable logic devices aren't allowed.
> > >
> > > Four 74HC123s will do it, but are too big.
> > > Four window comparators monitoring the signal through an RC will do it,
> > but
> > > also seems too big.
> > >
> > > Is four schmitt trigger XOR gates with four RC's the smallest
> > > implementation?
> > >
> > > I was thinking some sort of analog implementation might be able to do
> it
> > > smaller. But AC coupling the four signals together would allow them to
> > > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > > better?
> > >
> > > Regards,
> > > Jason White
> > > --
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
> >
> >
> > --
> > - Forrest
> > --
> > 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
>


--
- Forrest
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Jason White-20
In reply to this post by Brent Brown-2
Hello Brent,

It's a good idea and I wish I could do it. But there's a problem that I
haven't reconciled - under many circumstances the inputs can change at the
exact same time with the exact same slew rate and cancel out.

Am I correct in thinking that for this implementation to avoid signals
canceling out I would have to set the summing coefficients for each
resistor to be different such that cancelation is not possible. I would end
up with 16 unique voltage levels, one per combination.

Almost seems like an R2R ladder similar to a DAC in conjunction with two
comparators might be an option. An RC could provide a slow moving reference
voltage to the two comparators.

Am I thinking correctly about that particular implementation?

On Thursday, June 4, 2020, Brent Brown <[hidden email]> wrote:

> Hi Jason,
>
> How about: Sum the lines with 4 x resistors, feed this analog voltage into
> the +ve
> input of one comparator, and -ve input of another comparator. Remaining
> inputs to
> a C, with R to analog voltage above, where RC time constant sets pulse
> period.
> Combine comparator outputs with 2 x diodes and a pull-up or pull-down
> resistor as
> required.
>
> Brent.
>
> On 4 Jun 2020 at 16:35, Jason White wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital lines.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do it
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
>
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


--
Jason White
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Jason White-20
In reply to this post by David C Brown
Hi David,

I'm not permitted to use programmable electronic devices. I agree that it
would be a perfect application if they were allowed.

Latency of up to 20ms permissible.

On Friday, June 5, 2020, David C Brown <[hidden email]> wrote:

> How much latency is acceptable.  And is the output pulse retriggerable.
>
> Would using an 8 pin PIC to sample and digitally compare the inputs be too
> slow?
> With a 32MHz part you would be able  to keep the latency under a micro
> second.
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak                           Phone: 01663 733236
> Derbyshire                eMail: [hidden email]
> SK23 7ND          web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>
>
>
> *Sent from my etch-a-sketch*
>
>
> On Thu, 4 Jun 2020 at 21:38, Jason White <whitewaterssoftwareinfo@
> gmail.com>
> wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital lines.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do it
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
> >
> > Regards,
> > Jason White
> > --
> > 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
>


--
Jason White
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Jason White-20
In reply to this post by James Burkart-2
Hello James,

This circuit is involved in area where safety could conceivably be
concerned. I've been asked to avoid programmable devices even if it is
bigger/worse/etc.

On Friday, June 5, 2020, James Burkart <[hidden email]> wrote:

> I'm curious. Why not microcontrollers?
> --
> Sincerely,
>
> James Burkart
> *925.667.7175*
>
>
> On Thu, Jun 4, 2020 at 2:37 PM Jason White <
> [hidden email]> wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital lines.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do it
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
> >
> > Regards,
> > Jason White
> > --
> > 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] Detecting a change of level on four lines with digital logic/analog circuitry?

Jason White-20
In reply to this post by Justin Richards
Hello Justin,

You are correct. If all four signals were added together with the same
summing coefficients they would cancel out sometimes.

On Friday, June 5, 2020, Justin Richards <[hidden email]> wrote:

> Base on "The four signals can change at any time to any direction " then I
> must assume that 2 or more lines may transition at precisley the same time.
>
> Is that a correct assumption.
>
> Justin
>
> On Fri, Jun 5, 2020 at 4:38 AM Jason White <
> [hidden email]> wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital lines.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do it
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
> >
> > Regards,
> > Jason White
> > --
> > 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] Detecting a change of level on four lines with digital logic/analog circuitry?

Jason White-20
In reply to this post by Forrest Christian (List Account)
Hello Forrest,

I agree with you about the microcontrollers. Though, I can't change the
requirements.

Assuming that I can't find a smaller implementation (such as the analog
one) the XOR gates do look attractive.

On Friday, June 5, 2020, Forrest Christian (List Account) <
[hidden email]> wrote:

> It's too bad that programmable devices are not permitted...   This is
> perfect for an edge trigger on a microcontroller, or a tiny programmable
> logic device.   I would argue that using the functions available on a
> modern programmable device is going to be at least as reliable as any
> discrete logic/component solution.
>
> But...
>
> Take four xor gates (1 single 74hc86) each wired as a 'edge to glitch'
> converter - that is, wire each line directly to one input pin and through a
> rc filter to the other input pin.  This has the effect of slightly delaying
> the input to the second input pin, creating a situation where you get a
> brief pulse on the output on each edge as it catches up with the
> non-delayed first pin.
>
> You can then insert a diode into the output line, creating a 'wired or' for
> the output, so if *any* of the units have an edge, you get a pulse.
>  Direction of diode and whether you need a pullup/pulldown resistor is left
> as an exercise to the reader.
>
> Once you have that pulse, feel free to use an HC123 or a 555 to stretch it
> out.
>
> Or you could just try to convince whoever made the 'no programmable
> devices' policy that something like a PIC16F15313 which can be factory
> programmed by microchip is smaller, cheaper, and is just as reliable.
> Plus, it is highly likely that the entire function you describe can be done
> in one of the inbuilt "core independent peripherals" which wouldn't even
> require the core to be running, and the latency if done right wouldn't be
> any more than the discrete solution.  Or you can save a few cents if you
> can tolerate a bit of interrupt latency.  Of course, I can understand that
> sometimes in an application the 'black box' nature of a programmable device
> isn't really possible to use.  But those applications are typically the
> type where you're going to have to qualify everything.
>
> On Thu, Jun 4, 2020 at 2:47 PM Jason White <
> [hidden email]> wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital lines.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do it
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
> >
> > Regards,
> > Jason White
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> - Forrest
> --
> 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] Detecting a change of level on four lines with digital logic/analog circuitry?

David C Brown
In reply to this post by Jason White-20
If you use the solution proposed by fForest and amendment by me you would
be OK..  Each XOR gate output would be a pulse and you are ORing them so
even if tow changed together you would get a pulse out of the or gate
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: 01663 733236
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Fri, 5 Jun 2020 at 11:44, Jason White <[hidden email]>
wrote:

> Hello Brent,
>
> It's a good idea and I wish I could do it. But there's a problem that I
> haven't reconciled - under many circumstances the inputs can change at the
> exact same time with the exact same slew rate and cancel out.
>
> Am I correct in thinking that for this implementation to avoid signals
> canceling out I would have to set the summing coefficients for each
> resistor to be different such that cancelation is not possible. I would end
> up with 16 unique voltage levels, one per combination.
>
> Almost seems like an R2R ladder similar to a DAC in conjunction with two
> comparators might be an option. An RC could provide a slow moving reference
> voltage to the two comparators.
>
> Am I thinking correctly about that particular implementation?
>
> On Thursday, June 4, 2020, Brent Brown <[hidden email]> wrote:
>
> > Hi Jason,
> >
> > How about: Sum the lines with 4 x resistors, feed this analog voltage
> into
> > the +ve
> > input of one comparator, and -ve input of another comparator. Remaining
> > inputs to
> > a C, with R to analog voltage above, where RC time constant sets pulse
> > period.
> > Combine comparator outputs with 2 x diodes and a pull-up or pull-down
> > resistor as
> > required.
> >
> > Brent.
> >
> > On 4 Jun 2020 at 16:35, Jason White wrote:
> >
> > > Hi everyone,
> > >
> > > I have an application where I need to generate at pulse least 1
> > microsecond
> > > long any time a rising or falling edge is detected on four digital
> lines.
> > > The four signals can change at any time to any direction. The pulse is
> > used
> > > to trigger a timer providing a reset signal to the rest of the system.
> > > Microcontrollers and programmable logic devices aren't allowed.
> > >
> > > Four 74HC123s will do it, but are too big.
> > > Four window comparators monitoring the signal through an RC will do it,
> > but
> > > also seems too big.
> > >
> > > Is four schmitt trigger XOR gates with four RC's the smallest
> > > implementation?
> > >
> > > I was thinking some sort of analog implementation might be able to do
> it
> > > smaller. But AC coupling the four signals together would allow them to
> > > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > > better?
> >
> >
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> Jason White
> --
> 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] Detecting a change of level on four lines with digital logic/analog circuitry?

Brent Brown-2
In reply to this post by Jason White-20
I don't know if your thinking is correct, only that it is similar to mine ;-)Does seem like having 16 unique voltage levels would avoid simultaneously changing signals going un-noticed. Then I start to wonder if the slowly tracking comparator reference level might result in a mis-detection in some scenario. Another factor to throw in is need for hysteresis to prevent comparator oscillation.Feels like it might be the start of an idea. I'd want a Spice simulation or a bread-board test to convince myself it's worth pursuing, or not.
-------- Original message --------From: Jason White <[hidden email]> Date: 6/5/20  10:50 PM  (GMT+12:00) To: "Microcontroller discussion list - Public." <[hidden email]> Subject: Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry? Hello Brent,It's a good idea and I wish I could do it. But there's a problem that Ihaven't reconciled - under many circumstances the inputs can change at theexact same time with the exact same slew rate and cancel out.Am I correct in thinking that for this implementation to avoid signalscanceling out I would have to set the summing coefficients for eachresistor to be different such that cancelation is not possible. I would endup with 16 unique voltage levels, one per combination.Almost seems like an R2R ladder similar to a DAC in conjunction with twocomparators might be an option. An RC could provide a slow moving referencevoltage to the two comparators.Am I thinking correctly about that parti!
 cular implementation?On Thursday, June 4, 2020, Brent Brown <[hidden email]> wrote:> Hi Jason,>> How about: Sum the lines with 4 x resistors, feed this analog voltage into> the +ve> input of one comparator, and -ve input of another comparator. Remaining> inputs to> a C, with R to analog voltage above, where RC time constant sets pulse> period.> Combine comparator outputs with 2 x diodes and a pull-up or pull-down> resistor as> required.>> Brent.>> On 4 Jun 2020 at 16:35, Jason White wrote:>> > Hi everyone,> >> > I have an application where I need to generate at pulse least 1> microsecond> > long any time a rising or falling edge is detected on four digital lines.> > The four signals can change at any time to any direction. The pulse is> used> > to trigger a timer providing a reset signal to the rest of the system.> > Microcontrollers and programmable logic devices aren't allowed.> >> > Four 74HC123s will do it, but are too big.> > Four window comparators monitoring the sig!
 nal through an RC will do it,> but> > also seems too big.> >> > Is four schmitt trigger XOR gates with four RC's the smallest> > implementation?> >> > I was thinking some sort of analog implementation might be able to do it> > smaller. But AC coupling the four signals together would allow them to> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it> > better?>>> --> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive> View/change your membership options at> http://mailman.mit.edu/mailman/listinfo/piclist>-- Jason White-- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archiveView/change your membership options athttp://mailman.mit.edu/mailman/listinfo/piclist
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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

David C Brown
In reply to this post by Jason White-20
How should the system react if one of the inputs changes after another
input has triggered the 1mS pulse?
Or to put it another way: how should the system react if there were changes
on one or other of the inputs every 500uS.
__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak                           Phone: 01663 733236
Derbyshire                eMail: [hidden email]
SK23 7ND          web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*


On Thu, 4 Jun 2020 at 21:38, Jason White <[hidden email]>
wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microsecond
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is used
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, but
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?
>
> Regards,
> Jason White
> --
> 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] Detecting a change of level on four lines with digital logic/analog circuitry?

Peter Onion
In reply to this post by Jason White-20
On Thu, 2020-06-04 at 16:35 -0400, Jason White wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microsecond
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is used
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, but
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?
>
> Regards,
> Jason White

Thread is now TL:DR so sorry if this has been suggested already.

Feed each signal into a two bit shift register. Xoring the two outputs will give you a
pulse on each transition.  Clock the shift register fast enough to ensure you catch the
shortest pulses on the inputs.   Or the xor outputs together and trigger your monostable
with that.

PeterO
 

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Re: [EE] Detecting a change of level on four lines with digital logic/analog circuitry?

Jason White-20
In reply to this post by David C Brown
Hello David,

I'm actually only after a 1 microsecond long pulse. I need signal to go
high for 1us every time the inputs change. So if a change occurs during
that 1us output pulse the pulse needs extended.

On Fri, Jun 5, 2020 at 11:02 AM David C Brown <[hidden email]> wrote:

> How should the system react if one of the inputs changes after another
> input has triggered the 1mS pulse?
> Or to put it another way: how should the system react if there were changes
> on one or other of the inputs every 500uS.
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak                           Phone: 01663 733236
> Derbyshire                eMail: [hidden email]
> SK23 7ND          web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>
>
>
> *Sent from my etch-a-sketch*
>
>
> On Thu, 4 Jun 2020 at 21:38, Jason White <
> [hidden email]>
> wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital lines.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do it
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
> >
> > Regards,
> > Jason White
> > --
> > 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] Detecting a change of level on four lines with digital logic/analog circuitry?

Jesse Lackey
In reply to this post by Jason White-20
Ah yes ... either Medical or Aerospace/Military, avoiding triggering
(pardon the pun) a software validation/verification requirement (a big
deal).  I've had to play these games when upgrading medical gear at a
previous job, fun up to a point.  For medical programmable logic did not
count in the "software" realm, since it did not have a CPU, and
apparently the auditor and our CTO had scuffle over where the line was.
The CTO prevailed, but all this was designed 10+ years ago.

It is deeply ironic when one has to design weirdo things in order to
avoid onerous safety verification procedures that much more
understandable/conventional basic logic/code would require.

J


Jason White wrote:

> Hello James,
>
> This circuit is involved in area where safety could conceivably be
> concerned. I've been asked to avoid programmable devices even if it is
> bigger/worse/etc.
>
> On Friday, June 5, 2020, James Burkart <[hidden email]> wrote:
>
>> I'm curious. Why not microcontrollers?
>> --
>> Sincerely,
>>
>> James Burkart
>> *925.667.7175*
>>
>>
>> On Thu, Jun 4, 2020 at 2:37 PM Jason White <
>> [hidden email]> wrote:
>>
>>> Hi everyone,
>>>
>>> I have an application where I need to generate at pulse least 1
>> microsecond
>>> long any time a rising or falling edge is detected on four digital lines.
>>> The four signals can change at any time to any direction. The pulse is
>> used
>>> to trigger a timer providing a reset signal to the rest of the system.
>>> Microcontrollers and programmable logic devices aren't allowed.
>>>
>>> Four 74HC123s will do it, but are too big.
>>> Four window comparators monitoring the signal through an RC will do it,
>> but
>>> also seems too big.
>>>
>>> Is four schmitt trigger XOR gates with four RC's the smallest
>>> implementation?
>>>
>>> I was thinking some sort of analog implementation might be able to do it
>>> smaller. But AC coupling the four signals together would allow them to
>>> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
>>> better?
>>>
>>> Regards,
>>> Jason White
>>> --
>>> 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] Detecting a change of level on four lines with digital logic/analog circuitry?

Denny Esterline-2
I've mentioned it before, but some of my product ends up installed in power
plants. Some of those plants are fueled with fissionable material...
Even though I'm nowhere near the "fun" parts, even the discussion of
whether or not we need to comply with those software requirements was
deemed so onerous that we designed with a half dozen discrete logic gates
instead of a micro.

The standing joke is that our entire product costs less than the paperclip
budget for the compliance process.



On Thu, Jun 11, 2020 at 8:44 AM Jesse Lackey <[hidden email]>
wrote:

> Ah yes ... either Medical or Aerospace/Military, avoiding triggering
> (pardon the pun) a software validation/verification requirement (a big
> deal).  I've had to play these games when upgrading medical gear at a
> previous job, fun up to a point.  For medical programmable logic did not
> count in the "software" realm, since it did not have a CPU, and
> apparently the auditor and our CTO had scuffle over where the line was.
> The CTO prevailed, but all this was designed 10+ years ago.
>
> It is deeply ironic when one has to design weirdo things in order to
> avoid onerous safety verification procedures that much more
> understandable/conventional basic logic/code would require.
>
> J
>
>
> Jason White wrote:
> > Hello James,
> >
> > This circuit is involved in area where safety could conceivably be
> > concerned. I've been asked to avoid programmable devices even if it is
> > bigger/worse/etc.
> >
> > On Friday, June 5, 2020, James Burkart <[hidden email]> wrote:
> >
> >> I'm curious. Why not microcontrollers?
> >> --
> >> Sincerely,
> >>
> >> James Burkart
> >> *925.667.7175*
> >>
> >>
> >> On Thu, Jun 4, 2020 at 2:37 PM Jason White <
> >> [hidden email]> wrote:
> >>
> >>> Hi everyone,
> >>>
> >>> I have an application where I need to generate at pulse least 1
> >> microsecond
> >>> long any time a rising or falling edge is detected on four digital
> lines.
> >>> The four signals can change at any time to any direction. The pulse is
> >> used
> >>> to trigger a timer providing a reset signal to the rest of the system.
> >>> Microcontrollers and programmable logic devices aren't allowed.
> >>>
> >>> Four 74HC123s will do it, but are too big.
> >>> Four window comparators monitoring the signal through an RC will do it,
> >> but
> >>> also seems too big.
> >>>
> >>> Is four schmitt trigger XOR gates with four RC's the smallest
> >>> implementation?
> >>>
> >>> I was thinking some sort of analog implementation might be able to do
> it
> >>> smaller. But AC coupling the four signals together would allow them to
> >>> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> >>> better?
> >>>
> >>> Regards,
> >>> Jason White
> >>> --
> >>> 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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