[En-Nut-Discussion] 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: en-nut-discussion-bounces at egnite.de
[mailto:en-nut-discussion-bounces at egnite.de] On Behalf Of William Baker
Sent: Monday, June 13, 2005 12:44 PM
To: en-nut-discussion at egnite.de
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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