Hi,
My burglar alarm has a landline dialler interface to notify me when the alarm is triggered, but I don't have a landline in my house.
I reckon it must be possible to make my own interface from the alarm to an old mobile phone, so that when the alarm is triggered, it dials me on the mobile instead.
Sounds like a job for digispark!
I have a couple of old Nokia phones that (Nokia N73 or Nokia 6210) both of which have speed dial function, making them VERY easy to canabalise to dial any number (in theory!). Long pressing any number keys dials a pre-stored number with just the one key.
My thought is that I can solder wires under any chosen digit key (probably the "9" since that button is already broken off), and also under the hang up button. Shorting the "9" key's wires, will initiate the call. Shorting the hangup button's wires will end the call.
The code for the digispark to dial out should be very easy, since that is a just 3 step process. Will probably consist of when triggered from the alarm, momentary press hangup (to wake phone). Long press 9 key (for say 1 sec) to initiate quick dial of pre-stored number. After a set delay (maybe 20 secs), press hang up again.
I figure this will work well since the call will be made from a pre-pay sim which will be a dedicated number used only by my alarm. Therefore when I get the call from that number, I'll know what has called me, so won't matter that is it just a silent call! However, I suspect in an alarm situation, the internal sounder will be loud enough to be heard through the mobile's microphone, so will give me a siren down the call. If that works, as suspected, then I could also choose to have the alarm sysetm call me for other reasons too (when siren is not sounding) , as I would potentially be able to distinguish between the siren sounding and not sounding. Perhaps configuring the alarm panel to give me a call for a fringe case that I wouldn't want the main alarm to sound for!
I'm not sure there is an easy way to use the existing dialler feature of the alarm, so I'm most likely to use one of the main relay outputs from the alarm as the trigger. These give a 12v output feed when the alarm is sounded. I see two options for using these to trigger the digispark to dial:
- Simplest is to canabalise a USB car adapter to power the digispark from the 12v feed, so that the digispark is off until the alarm is triggered. Then it would power on, auto boot and auto run the script when powered up by the alarm output.
- However slightly more flexible, but more complicated wiring, would be for the digispark to always be running waiting for the 12v triggering signal as an input. This would allow the digispark program to potentially do other things too.
The part I am most stumped by is the interface from the digispark to the phone key wires. I am guessing this should be a transistor on one digital output each (one for hangup and one from the number key chosen - probably "9". I guess if I used 3 outputs, I could even get the program to dial 2 numbers in sequence, by using 2 of the speed dials:- say "8" and "9"). What sort of arrangement should I be thinking of from digispark to phone button wires? Could I get away with running a common ground between the two devices (digispark and phone) and just running a voltage (or sinking a voltage) to the appropriate wire, or should I run it through a transistor to short the two wires per button?
Can anyone here help with the transistor arrangement and wiring?
I'll try to open the phone in the next day or so, and play with a multimeter to see if I can figure out whether it is grounding to trigger the button, or feeding it a voltage to trigger it.... or if as I guess if it is neither, but instead some sort of matrix arrangement, then it will definietly need to be a transistor to short the two wires.
The other part I would need help with would be if I chose not to power the digispark from the 12v triggered output, and instead wanted that running as an input feed, I'd need to suitably interface that 12v signal as an input to the digispark, so I didn't blow the digispark input. Again, I suspect this is another transistor!
I am planning to do some background reading too, but wanting to get this thread running too to document the process.
Keen to get a working prototype in the coming days, as I want some remote alarm coverage of my property this week if I can....
Thanks for your interest.
Mike
