Thank you all for your suggestions. To answer some of your
questions/comments:


- We're working on a device that has the ability to be powered from the COM
port, as well as another 12V source. We're simultaneously developing
software that will work in conjunction with the device. Among other things,
the software controls the states of each of the control lines, and monitors
the input pins. Simular projects are likely to take place in the near
future, so the breakout box is likely to see long-term use.

- The "dual LEDs/resistors" breakout box someone has suggested draws too
much current, and causes a significant voltage drop, to the point where the
device fails to start (it is continually resetting). So the box has to have
a relatively high impedance, so as to minimize its effect on the RS232
lines.

- Someone correctly hinted that developers' time is expensive. Since the
final product will be produced in very limited quantities, it's important to
keep the development time to a minimum (no tinkering, if possible), but
parts cost is not an issue. The circuit design doesn't need to be clever, it
just has to work.

- LEDs must be able to indicate +/- levels on RS232 lines, as well as the
"no signal" condition.


We've settled on using eight MAX221s (one per line), each of which has an
#INVALID output that goes high whenever there's voltage on the respective
control or data line. The pin goes low whenever the voltage is in the
undefined region.

LEDs are the RGY kind. The #INVALID pin is connected through an inverter to
the Gnd pin of the LED (to disable it when the signal is not present).

The Rout pin of the MAX221 is fed into a buffer and an inverter, the outputs
of which are connected to G and R pins of the LED.

Wasteful and unelegant, I know. :)


I'm saving the entire thread, there's another "breakout box" project
(non-RS232) that we've had on our to-do list for a while, which may utilize
some of the interesting ideas presented here. So thank you again for your
input.

Sincerely,

Vitaliy


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