Robert Rolf wrote:
>I take it that you've never heard of 2 pin bicolor LEDs?
> Commonly used on RS232 break out boxes to do exactly what
> you are asking. One LED + one current limiting resistor per signal line.
> RS232 spec says up to 30mA supplied. LED lights with a few mA
> so you drive the LED DIRECTLY from the RS232 signal lines.
> One polarity gives you red. The other, green, and no voltage
> is black.

I have a breakout box from B&B Electronics, which is designed exactly this 
way. However, first of all -- good luck drawing 30 mA from a serial port... 
maybe at 0V, and only with *some* ports. Second, and I should have probably 
mentioned it, I would like to affect the lines as little as possible. We 
have designs which are powered from the port, and it's not a good idea to 
add more load to the port (voltage drops below threshold).

> Why are you trying to do it the "REALLY HARD WAY' with the
> Maxim device? LED don't care too about voltage. Just current.

See above.

> A bunch of LM339 comparators, with bias at RS232 thresholds
> (+3V, -3V, is spec) will let you drive the LEDs directly (with
> current limits of course) if you really need a buffered solution.
> And remember that you only need ONE current limiting resistor per
> pair of LEDs since only one is on at a time.

Any other ideas?

Best Regards,

Vitaliy 

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