You might want to consider changing the LEDs to something other than
red/green.  8% of people have some form of color blindness, and
red-green color blindness is the most popular at 1 in 20 males (5%).

If nothing else, please choose very high brightness frosted (not
clear) LEDs, and a green color that tends towards yellow.

-Adam

On 4/21/07, Vitaliy <spam@maksimov.org> wrote:
> 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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