William Chops Westfield wrote:
>> I'm helping a co-worker design an improved RS232 breakout
>> box (for in-house use), which will have an LED for each
>> of the lines (except ground). Each LED has three states:
>> Green (active), Red (inactive), and Off (no signal).
>>
>> What is the most straightforward way to implement this?
>>
> 
> Without loading the port, eh?  You should be able to bias
> NPN and PNP transistors (or mosfets, or logic gates) so that
> one gate is on if the signal is negative, one if the signal is
> positive, and neither if the signal is absent.  You may have to
> abuse or provide protection diodes for rs232, though. See the
> attached schematic (which is actually for a logic probe of ancient
> vintage.)

This solution would require a negative supply to work with RS232.

> With a PIC, I'd be tempted to use A-D converter pins for inputs
> and detect actual voltages, then display digitally...  This might
> turn out easier, and you could do something like yellow for voltages
> present but not within legal range...

Same problem.

Vitaliy
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