[En-Nut-Discussion] 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" <bbaker at priefert.com>
>To: <en-nut-discussion at egnite.de>
>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
>>
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