[HomeBrew] Two color LEDs

[Ian Wilson]

The simplest solution is probably to use a quad half-bridge such as the
L293D (http://www.alltronics.com/download/1330.pdf).
If this is too expensive, you can lash up two half bridges using one NPN and
one PNP transistor each, with an inverter between them.
In each half bridge, the collectors and bases of the PNP and NPN connect
together.  Emitter of the PNP goes to the +rail.  Emitter of
the NPN goes to ground.  The output is taken from the point where the
collectors are joined. Connecting the bases (through a resistor)
to +rail turns on the NPN and turns off the PNP.  Vice versa if you connect
the bases to ground.

A motor, or two-color LED, would be connected between two half bridges.

The L293D is simpler though :)

Hope this helps,

--ian K3IMW/6

> Does anyone have a simple circuit for driving dual color (red/green)
LED's?  That is, the two leaded kind which are red polarized
> one way(e.g. +/-) and green the other (-/+).  No relays please.  I'm
looking for solid state solution.

> Op amp's can reverse output polarity, but they're usually pretty low
current.  Need about 10 to 20 mA for most LEDs.