Troubleshooting DSC Alarm Panel Interface

Hi! Can you please help me troubleshoot my Arduino Uno circuit? It interfaces with my alarm system and sends via WiFi the alarm messages to an MQTT broker. I use the relay to detect when the alarm fires by detecting the signal the alarm panel sends to the siren. The alarm has 12v logic so I use 10kohms voltage dividers to drop the voltage going to digital inputs 2 and 4. Everything worked fine for a few days but then the Arduino got fried. I haven’t been able to pinpoint the problem.

Any help would be greatly appreciated. Thanks

Hi, How have you got the siren relay wired?

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png? (Not a fritzy diagram)

Thanks.. Tom.. :)

TomGeorge, here you go.

If voltage on DATA is 12V, voltage on pin 4 is 6V, too much, 5.5V MAX, make R2 & R4 6.8K.

OP’s circuit.

If you want to use that relay sensing the siren, then I suggest my modification, this will completely isolate the BELL from the UNO, 10K might work,if not try 4k7 , or 1k.
Modified Circuit.
Arduino Alarm Circuit1.jpg

As outsider has said, you need to recalculate your potential divider to get 12V to 5V.

Tom… :slight_smile:

Tom, Outsider, thank you for your help.


Hi György,

I want to connect to my DSC from my Arduino. What do you think, can I connect right before the Keypad? It is easily accessible to me, the main alarm not.

My other question: DSC doesn't complain about the Arduino? I read somewhere that keypads are programmed to the alarm, if you remove or add one then you must pair it with master code.