protecting inputs

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protecting inputs

William Baker
I am trying to protect the inputs on my Ethernut.  Under normal
circumstances, the inputs should be wired to a nice protected TTL
friendly 5V circuit.  However, this is an industial environment and
there is a lot of 24V circuitry on the device.  I am sure that circuits
will be misconnected/shorted during assembly/maintenance/testing of the
equipment.

I'm happy to add a friendly daughter-board with screw connectors, but am
unsure about the circuitry.  I need the device to survive a temporary
24V misconnection to any of the digital inputs.  Zener's and resistors?  
Unity gain op-amp?  I'm a software guy with only passing knowledge of
hardware.

Any recommendations?

I realize this an electronic question and not 100% on topic.  Please excuse.

bbaker

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RE: protecting inputs

William Basser
I would recommend using opto isolators.  They are inexpensive and provide
isolation from outside voltages coming into a Micro pin.  I have attached a
schematic for your perusal.

Bill Basser
Cyber Integration, LLC

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of William Baker
Sent: Monday, June 13, 2005 12:44 PM
To: [hidden email]
Subject: [En-Nut-Discussion] protecting inputs

I am trying to protect the inputs on my Ethernut.  Under normal
circumstances, the inputs should be wired to a nice protected TTL
friendly 5V circuit.  However, this is an industial environment and
there is a lot of 24V circuitry on the device.  I am sure that circuits
will be misconnected/shorted during assembly/maintenance/testing of the
equipment.

I'm happy to add a friendly daughter-board with screw connectors, but am
unsure about the circuitry.  I need the device to survive a temporary
24V misconnection to any of the digital inputs.  Zener's and resistors?  
Unity gain op-amp?  I'm a software guy with only passing knowledge of
hardware.

Any recommendations?

I realize this an electronic question and not 100% on topic.  Please excuse.

bbaker

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Re: protecting inputs

Andrea Cannavicci
In reply to this post by William Baker
Normally, when you must interface a digital board (TTL or LVTTL) to any
environment
that use non-TTL voltage level the best protection is to use photocoupler.
This is possible if the interface signals are quite slow (<100Khz). For fast
signals you can use open-collector transistor (I use 2n2222).
Note that this type of protection can be use for non-bidirectional signal.
Simple resistor and diodes are a possible solution, but not 100% effective.

If you want I can send you same protection circuit example I have used and
debugged.

Andrea Cannavicci.


----- Original Message -----
From: "William Baker" <[hidden email]>
To: <[hidden email]>
Sent: Monday, June 13, 2005 7:43 PM
Subject: [En-Nut-Discussion] protecting inputs


> I am trying to protect the inputs on my Ethernut.  Under normal
> circumstances, the inputs should be wired to a nice protected TTL
> friendly 5V circuit.  However, this is an industial environment and
> there is a lot of 24V circuitry on the device.  I am sure that circuits
> will be misconnected/shorted during assembly/maintenance/testing of the
> equipment.
>
> I'm happy to add a friendly daughter-board with screw connectors, but am
> unsure about the circuitry.  I need the device to survive a temporary
> 24V misconnection to any of the digital inputs.  Zener's and resistors?
> Unity gain op-amp?  I'm a software guy with only passing knowledge of
> hardware.
>
> Any recommendations?
>
> I realize this an electronic question and not 100% on topic.  Please
excuse.
>
> bbaker
>
> _______________________________________________
> En-Nut-Discussion mailing list
> [hidden email]
> http://www.egnite.de/mailman/listinfo.cgi/en-nut-discussion

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Re: protecting inputs

Vincent Gijsen
Optocouplers are indeed a good idee to protect your inputs but you could
try the stuff below.

Maybe another thought: Relais, they are quiet slow, but galvanical
separated (i'm not sure galvanical is a correct english word ;)) and
they are available in 24V so that whould be easy interfacing with te
rest of your stuff.

Another possibility is a Triac.


Andrea Cannavicci wrote:

>Normally, when you must interface a digital board (TTL or LVTTL) to any
>environment
>that use non-TTL voltage level the best protection is to use photocoupler.
>This is possible if the interface signals are quite slow (<100Khz). For fast
>signals you can use open-collector transistor (I use 2n2222).
>Note that this type of protection can be use for non-bidirectional signal.
>Simple resistor and diodes are a possible solution, but not 100% effective.
>
>If you want I can send you same protection circuit example I have used and
>debugged.
>
>Andrea Cannavicci.
>
>
>----- Original Message -----
>From: "William Baker" <[hidden email]>
>To: <[hidden email]>
>Sent: Monday, June 13, 2005 7:43 PM
>Subject: [En-Nut-Discussion] protecting inputs
>
>
>  
>
>>I am trying to protect the inputs on my Ethernut.  Under normal
>>circumstances, the inputs should be wired to a nice protected TTL
>>friendly 5V circuit.  However, this is an industial environment and
>>there is a lot of 24V circuitry on the device.  I am sure that circuits
>>will be misconnected/shorted during assembly/maintenance/testing of the
>>equipment.
>>
>>I'm happy to add a friendly daughter-board with screw connectors, but am
>>unsure about the circuitry.  I need the device to survive a temporary
>>24V misconnection to any of the digital inputs.  Zener's and resistors?
>>Unity gain op-amp?  I'm a software guy with only passing knowledge of
>>hardware.
>>
>>Any recommendations?
>>
>>I realize this an electronic question and not 100% on topic.  Please
>>    
>>
>excuse.
>  
>
>>bbaker
>>
>>_______________________________________________
>>En-Nut-Discussion mailing list
>>[hidden email]
>>http://www.egnite.de/mailman/listinfo.cgi/en-nut-discussion
>>    
>>
>
>_______________________________________________
>En-Nut-Discussion mailing list
>[hidden email]
>http://www.egnite.de/mailman/listinfo.cgi/en-nut-discussion
>
>
>  
>

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