On Apr 19, 2007, at 5:14 PM, Vitaliy 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.)

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...

BillW
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