cosax
Posts: 13
Joined: Tue Apr 30, 2013 1:18 pm

Extend current security alarm system

Thu May 09, 2013 4:56 am

Hello everybody,

I have just started experimenting with the pi and I have a question (which may sound silly...). I have a simple security alarm system at home and I would like to extend its functionality by connecting "in parallel" the raspberry pi, possibly together with piface. So, I would like each PIR to connect to both the existing system as well as pi. This will allow me to gradually add functionality (eg. logging or sending emails on events, something that my current systems doesn't support) while keeping the current system for driving the bell, handling the keypad, powering the PIRs, making calls etc. Is this possible? Can a PIR physically connect to 2 systems? Do I need to build some kind of opto-isolation?

Thanks in advance for your help!

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Posts: 121
Joined: Wed Oct 17, 2012 10:10 pm
Location: Brisbane Australia

Re: Extend current security alarm system

Fri May 10, 2013 8:22 am

I've essentially done the same thing very recently with my piface. Had originally planned to wire the PIR contacts in parallel to my RPi+PiFace and my existing system but I discovered the PIRs had line end resistors in series with the NC contacts so I decided to completely rip out the existing system and remove those resistors from all the PIRs. If your existing system only reads NC contacts, then you may be ok but you should check the open contact voltage on your existing system to ensure it is around the 5V used on the PiFace otherwise (I guess) you risk damaging the PiFace board.

My RPi software sends emails (including to sms gateway) on alarm and is completely web based. I also used a $7 ebay USB numeric keyboard for optional direct entry. The PiFace drives a siren screamer directly. It you are like me you will have a box full of old plug pack power supplies so I just used an 12V, 1A power supply to power the PIRs and siren. In fact, I also used an old 5V supply I had and wired it to the PiFace board to back feed the RPi as well, i.e. not through the microusb. I did not use anything from the existing system except the PIRs and their wiring.

I plan to post all my software and installer script to github soon and will post a blog about my setup.

cosax
Posts: 13
Joined: Tue Apr 30, 2013 1:18 pm

Re: Extend current security alarm system

Sat May 11, 2013 1:17 pm

Thanks for you answer. Sounds like you have built a very good system.

I have checked my existing security system and there are no EOL resistors installed for the PIRs. Also the open contact voltage is 5V. So, if I were to pursue my original idea, can I connect each PIR to the existing and to the RPi/piface at the same time?

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Posts: 121
Joined: Wed Oct 17, 2012 10:10 pm
Location: Brisbane Australia

Re: Extend current security alarm system

Sat May 11, 2013 10:33 pm

I think that would be ok.

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