[sdiy] Module input isolation?

[John Speth]

>     What you need to add greatly depends on the chip and what you need
> to do.  For bringing out an LM311 input pin, I would have a 
> resistor in
> series with the pin (1K -> 10K range I would think), and then 
> you would
> want to have back to back diodes (like 1n914's) from the + to - input,
> plus clamp diodes to the two power supply rails ( two diodes,  Cathode
> of D1 to V+, Anode D1 to input, Cathode D2 to input, Anode of 
> D2 to V-,
> per input).  Doing all this will probably make the thing 
> close to bullit
> proof.

What does the back/back diodes do?

JJS
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