A few weeks ago my home alarm system went into repairmode because of one empty battery.
The system was already in place when i bought the appartment and the previous owners lost the master code. Now i can either pay €500 to replace the battery and reset/reprogram the system or i can build my own cheaper system on to the existing doorsensors. Something i can ARM and DISARM using SMS and that sends alerts via SMS.
(Thinking about using a Adafruit 32u4 FONA powered with via USB-charger with a battery as a backup.)
I measured the doorsensors with a continuity test, expecting they just are reedswitches that close when the door is closed, but i found out they have a resistance of about 5K Ohm when closed and 10K ohm when opened. Any idea how i program this?
I have some experience with Arduino UNO R3, i know this may sound ambitious for a beginner but i'm happy to learn.
Is it an old system? More usually passive infrared sensors are used for alarms with contacts limited to the external doors.
Are all the door contacts wired in series or is the area divided up into multiple zones which you would want to control separately ?
Even if the alarm is not active, you may still want to monitor the door circuit(s) for continuity so you are warned immediately if there is a fault.
You should be able to easily simulate the whole thing on a breadboard, with each door contact being represented by a pair of 5k resistors. Short one of the resistors in the pair out to simulate a closed door.
Once you have that right, then start with the SMS part.
Ah the tamperproofing with resistance makes sense.
It's about 6 years old.
Euromatec 6.6 main board.
The PIR is a Euromatec SRX1000M.
It's a small appartment with one PIR detector (very sensitive and wide view) and contacts limited to doors with handles on both sides.
I don't know if i can make the PIR work with the 32u4 but i'll have a look.
How would i monitor the doors for errors without being alerted everytime i open the door to my garden?
The PIR will probably be wired in a similar way to the contacts so that a short circuit or a cut wire triggers the alarm. It'll probably have 3 wires - 2 power and one signal (or 4 wires if there is a relay in it). Start by trying to measure the voltage when it detects something and also when there is nothing to detect.
You can monitor the door circuit for an open circuit fault all the time. The maximum resistance (if these are wired in series) is 10K times the number of doors. When the alarm is set, you naturally want to it to trigger when the resistance exceeds 5K times the number of doors.
Well it could be just a small buzzer. It doesn't have to go over the alarm route. That way, if there is a fault when you are at home (without the alarm being set) you are made aware of it.
