Magnetic Door Switch

Be careful to match the voltage and current before trying. Otherwise you could get blue smoke . To be sure, use isolation circuit  switch like this:

http://yourduino.com/sunshop2/index.php?l=product_detail&p=60

Clem

What is the open-circuit voltage at the zone terminals?

Will have a check with I get home tonight.

I was thinking there could be a potential issue if i linked to the terminals on the panel as the switch would have 2 live feeds...

Clem's right. My ancient alarm system feeds 12volts out to the switches (which are simple reed switches operated by a magnet screwed to the door). My system is a four wire system with two wires to 'make' contacts and the other two looped so that, if the cable is cut, the alarm goes off. It is not really necessary for the door switches, but is necessary for the contact mats.

Never connect anything like this directly to the Raspi. There are relay boards for the PI which would be fine for this application. Use a pin on the GPIO to operate the relay and let the relay contacts operate the alarm circuit. The only other issue is if the reeds are open or closed when the door is shut (they are probably closed as this is both cheaper and much more reliable. If you get a relay board with changeover contacts rather than just make contacts you can be sure you won't have to keep powering the relay to keep the alarm off.

The solid state switch that Clem suggests is overkill for what you want to do and does not isolate the earth connection from the Raspi. I found this for £1.14.

FACILLA 5V 2-Channel Relay Module Shield for: Amazon.co.uk: Electronics

Be warned, though, it is 'make' contacts, only, which probably means you are going to need it powered on to stop the alarm.

Or you could make something up with this 5 volt relay from Farnel.

30.22.7.005.0010 - FINDER - RELAY, POWER, PCB, DPCO, 5V DC | CPC

It needs 40mA at 5 Volts to operate and has two changeover contacts. Magpi magazine has a simple circuit with a single transistor to drive a relay (you mustn't try directly from the GPIO pins). Or, try this circuit.

http://www.susa.net/wordpress/2012/06/raspberry-pi-relay-using-gpio/

If my thinking is right he is looking monitor the zone circuits, not trigger them.

His original discussion may shed some light on the subject: http://www.element14.com/community/thread/41234/l/raspberry-pi-and-existing-accenta-gen-4-alarm

Thanks guys!

The more I think about this, the more I'm going towards changing the alarm panel to one which  I can fully integrate with the PI.  Ideally using something like this AD2USB, The AlarmDecoder Store which taps in to the alarm panel ports used to monitor the alarm.  The only issue is that I can't find an alarm panel which is compatible with this device and available in the uk.

My goal is made of 2 parts, one is to use the existing PIRs and reed switches to use as inputs in the PI so I can control the lights in the house.  Secondly I'd like to monitor my alarm system and be able to change the state of the alarm remotely. ...

Thanks Paul, yes i'm looking to use the switch as an input.

Also royleith

Looking at the silkscreen on the relay module you pictures, there are changeover contacts on the relay.

The data sheet for the relay seems to confirm this: http://www.mycomkits.com/reference/Songle_SRD(T73)_Relay.pdf

You could wire it to the NC terminal and leave the relay de-energised.

Hi shyambhundia

Looks like an interesting module you've found there. I would investigate USB driver compatibility with the Pi before purchasing. You could also look into the RS232 version they produce.

Yep, thats on my checklist..But i've seen it being done on another blog..ill see if i can dig it out.  They also do a PI version too.

But I need to find a panel first