[sdiy] Bi-colour LED

[Jaroslaw Ziembicki]

----- Original Message -----
From: "Theo" <t.hogers at home.nl>
To: "Jaroslaw Ziembicki" <aon.912230836 at aon.at>; "Rob Keeble"
<rob at emulatorarchive.com>
Cc: "SDIY" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, July 03, 2004 5:40 PM
Subject: Re: [sdiy] Bi-colour LED


> 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.

Note: the circuit described here has a great property:
the CURRENT of the LEDs (instead of voltage) is proportional to the input
voltage. That means, the LEDs' nonlinearities don't matter.
Once more - my compliment, Theo...

Kind regards
Jarek