[En-Nut-Discussion] protecting inputs

[Andrea Cannavicci]

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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