[Soekris] How can I get a signal to the outside world?

Robert Woodcock rwoodcock at printinc.com
Mon Oct 13 14:03:02 UTC 2003

The GPIO lines are 3.3v, you can use that to switch a 12v relay using an
NPN transistor fed by a 10K resistor.

I did this earlier this year and posted my experiences to the list. Wiring
details and Linux userspace GPIO code are here:


-----Original Message-----
From: Curtis V. Schleich [mailto:cvslist at ccaonline.com]
Sent: Monday, October 06, 2003 6:53 AM
To: soekris-tech at lists.soekris.com
Subject: [Soekris] How can I get a signal to the outside world?

Here is my plan:  I've got a 4521 that rode out a lightning strike.  The
power input does not work, but feeding it with POE works fine.  PCMCIA
sockets are toast.  I want to use this as a "babysitter" board for a system
I've got in a pretty inaccessible place.  I'm using wisp-dist (but not
married to it...) I need to be able to trip a small relay to interrupt 12VDC
power to another 4521 for a few seconds.  I'm basically going to use a ping
test to see if the other soekris is connected to the head-end via the 802.11
card.  If it is not, I want to reboot the other (baby-sat) soekris board.

I've fiddled around to the point that I've got error led control, and I can
use that if someone can point me to a relay with a 1-2 VDC coil, or a
circuit diagram that will allow that 2VDC signal to control a 12VDC supply
voltage.  I've been working that angle with no luck.  The other idea is to
use the GPIO pins, but I've not found a driver for linux (kernel version
2.4.20, and I can compile if someone can get me source).  My last resort
will be to remove console from COM1, and use it, but I'd prefer to avoid
that approach if possible, mainly because of the boot sequence and the
resulting scenario of having no console (I'm not even sure I can do

Anyway, any input will be greatly appreciated.  I'll be glad to share any
resulting working system with the list.

Thanks, all!

Curtis V. Schleich,
CCA and CCAonline,
cvslist (at) ccaonline (dot) com

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