On 4/19/07, Vitaliy <spam@maksimov.org> 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?
>
> We have a solution using a MAX248 (which is also used to convert to TTL),
> and an inverter to drive LEDs, which takes care of the Green/Red
> functionality. However, we're having some difficulty with finding a simple
> and elegant solution that would turn the LED off.
>

I have doubts about the utility of such device but that is fortunately
yours (or your customer's) problem. The RS232 is able to deliver with
the worst driver around 5-10mA on lines without dropping the voltage
level required by the receiver (which is more than +/-3V).

If the specs say indeed 30mA then do not believe the RS232 specs.

So I guess no other gate or IC is requested for this implementation
except three leds and resistors ...(OK, maybe some transistors if you
really want).
As long the active is the inverse of inactive why must be both signalised ?
(christmas tree?) When there is no signal af course that both active
and inactive will be off.
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