I've got a burglar alarm that works off a 12V transformer. The only trouble is when the alarm is activated via the system it doesn't stop until the system code is entered into the keypad.
I'm wanting a circuit I can cut into the 12V siren feed (from the alarm unit) that will shut the alarm off after 20 minutes but will re-set when the voltage feed from the system is finally lost. It has been along time since I looked at electronic circuits so any advice would be greatly appreciated.
I have worked with 555 timers before. Could a monostable 555 timer be used for this application?
I'm looking for a not too overly complex solution that I can easily put together myself using breadboard.
Thank you for your time.
Regards, Mark Hodgkinson