I'm looking to use my Spark Core to control my door buzzer in my apartment. I'd like to identify the correct parts I need to build the required circuit, but this seems to be dependent on the voltage and current type that the buzzer system uses. I have been referencing this question: to try and identify the proper relay and transistor needed. Here is the schematic for my buzzer system (My apartment unit has model 3404 inside it with LISTEN, TALK, and DOOR buttons):
http://www.leedan.com/Pacific_AF-1000_Diagram.jpg
According to this similar example, I need to find a relay with a coil voltage equal to that of the door buzzer system. Also, as the Spark core provides 3.3 VDC, I believe I would need to amplify this using a transistor. From the schematic, can you help me identify what the voltage and type the system uses, and also what types of relay and transistor I would need for the circuit?
Many thanks!
Best Answer
simulate this circuit – Schematic created using CircuitLab
As noted in comments, the transistor can be any general purpose switching transistor. The transistor must be able to handle the current necessary to activate the relay coil. The relay coil must be able to be switched on by 3.3V. The relay must be capable of switching a 16 VAC load and be able to handle 0.625 Amps.
Note that the AC ground likely won't be connected to the Spark Core's ground because there shouldn't be a need and it could cause issues if you hook things up wrong.
A high signal from the Spark Core will activate the relay and activate the Buzzer. A low signal would block current in Q1 which would prevent RLY1 from activating which would prevent the buzzer from activating.