Hijacking simple intercom system buzzer - Page 1
Forum section: electronics / projects

author: pini.grigio
author_rank: Contributor
timestamp: August 14, 2024, 08:34:26 am
content: Hi,I have this somewhat old intercom system in my apartment - simple handset with a buzzer and two auxiliary buttons - one opens the main entrance and one is currently out of use.For the purpose of training my dog I'd like to commandeer the buzzer, so I can activate it without having someone downstairs ringing my apartment.I opened up the handset and I couldn't really make any sense of the wiring:I measured 17V on some of these lines (referenced to what I speculated was ground).Im not at all familiar with how these buzzers work - I'm assuming it's much like a relay.My plan was to probe the two terminals on the buzzer and see what signal is coming in when its activated, and then simply apply that signal myself.However I'm a bit hesitant as I wouldn't want to damage the intercom controller downstairs.Has anyone done anything like this and can offer advice?Thanks!

author: SuzyC
author_rank: Frequent Contributor
timestamp: August 14, 2024, 03:30:20 pm
content: Rather than trying to spend untold hours to figure this wiring puzzle out, why not record the sound of the buzzer on your smartphone and manually playback the recorded buzzer sound for your dog to hear.

author: Gyro
author_rank: Super Contributor
timestamp: August 14, 2024, 06:37:40 pm
content: Quote from: pini.grigio on August 14, 2024, 08:34:26 amThat's the problem, there's no way to guarantee not damaging the intercom controller. Looking at the photo, the buzzer looks like an AC driven one, so it isn't just a matter of putting the other button in parallel with anything.

author: madires
author_rank: Super Contributor
timestamp: August 14, 2024, 07:16:49 pm
content: It's a simple AC electromagnetic buzzer (typically 8-12 V). Usually one leg of the buzzer is connected to a common ground, and the other leg is switched by the doorbell button at the door directly to a transformer's secondary output tap (the other tap is connected to the common ground). That first tap isn't wired to the intercom telephone (just to the door station). So you can't power the buzzer via the intercom system from within the telephone.

author: pini.grigio
author_rank: Contributor
timestamp: August 15, 2024, 07:20:34 am
content: Quote from: madires on August 14, 2024, 07:16:49 pmUndoubtably the safest option, but I'd be missing out on the fun of experimenting with the intercom setupQuote from: Gyro on August 14, 2024, 06:37:40 pmQuote from: madires on August 14, 2024, 07:16:49 pmThanks.I broke out the scope and after some probing it seems like the orange line is ground - so the green wire presumably drives the buzzer with an AC signal?Im not quite sure why its also connected to the PCB, but the way this thing is wired up makes me question if its even wired up correctly.Seems like the best option would be to unplug the buzzer completely and drive it from some external source. Ill try and get a measurement of the incoming signal and recreate it using an RPi, a +-12V supply I have lying around and some FET

author: madires
author_rank: Super Contributor
timestamp: August 15, 2024, 11:30:02 am
content: The common ground should be also connected to the speaker, microphone and door opener switch. BTW, S2 could be wired for calling all tenants.