[sdiy] Bi-colour LED

[Theo]

Just one opamp, one resistor, the duo LED and two diodes (1N4048) will do.

Opamp + input to ground
Resistor is the input and goes to the opamp - input.
Now the feedback loop:
The anodes of the dual LED go to the output and - input of the opamp.
To the common cathode of the LEDs you connect the anodes of the diodes.
Cathodes of the diodes again connect to output and - input of the opamp.

If you scribble this on some paper you will see how it works immediately.
For each direction the blocking LED is bypassed with a diode.

HTH
Have fun,
Theo



----- Original Message -----
From: Jaroslaw Ziembicki <aon.912230836 at aon.at>


> ----- Original Message -----
> From: "Rob Keeble" <rob at emulatorarchive.com>
> To: <synth-diy at dropmix.xs4all.nl>
> Sent: Friday, July 02, 2004 9:27 PM
> Subject: [sdiy] Bi-colour LED
>
>
> > Hi,
> > I have found some rather nice blue/red bi-colour LED's (3 lead common
> > cathode) which I'd like to use for monitoring CV/signal amplitude in my
> > Modular synth. Red for + and blue for - voltages. Any ideas on how I can
> use
> > an Op Amp to drive these LED's, all the circuits I have seen are single
> LED
> > or 2 lead bi-colour.
>
> Hello,
> You will need 2 opamps, 2 diodes and 5 resistors.
> I can send you the schematics if you want.
>
> Regards,
> Jarek
>
>
>