[Soekris] How to drive external relays?

[Robert Woodcock]

On Thursday, September 07, 2006, Peter Bako wrote:
> Has anyone ever used a soekris box to drive a set of small relays?  I have
> a project in mind where I would have to control a small series of relays
> and be able to turn them on at pre-scheduled times and keep them on for
> anywhere from 1 to 45 minutes.  The relays would be used to send a larger
> voltage down the line to control end devices.  

Yes. Find a ribbon cable you can butcher and connect it to the GPIO header.
Connect each GPIO line to the base of an NPN transistor through a 10k ohm
resistor. Connect the emitters to ground. Connect the collectors to one
side of your relay coils. Connect the other side of your relay coils to
Vcc (accessible on JP3 on a 4501) through a 1 watt 20 ohm resistor (which
helps keep anything from blowing up if you short across the relay coils).

You should be able to find code in the list archives for any Soekris-
compatible OS to toggle the GPIO ports.