Dario Greggio wrote:

>>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... 

Especially a laptop port.
And many laptops don't even put out true RS232 levels. I've had problems with
Dells, HPs, Compaq's (the worst) where the signalling was BARELY over the 3V
thresold of the spec, (and the 1889 receivers commonly used).

> Me too would not "overload" the line hard-wiring Leds to it. (though it 
> may work, sure)
> The PIC approach from Timothy sounds the best, due to "minimum pulse 
> time" and some more features you can throw in as well.

You CAN draw enough to light LED's without causing a problem with the signal.
I've been doing it for decades now with an early break out box.
They wouldn't have sold 10's of thousands of them if they didn't work.
About $10.
What is his time worth?
It seems silly to convert from RS232 levels to TTL to JUST drive some
LEDs. And I certainly wouldn't use Maxim 'unobtainium' chips.
A a few transistors or fets are sufficient for the described task, turning on
LEDs based on one of three input levels.

And you certainly don't need expensive level shifting chips to convert RS232
levels to TTL. A zener diode and series resistor are sufficient.

R


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