Hi everyone,

My apartment has a Comelit handset that lets me press a button to open the front door after someone keys in my apartment number downstairs. I want to learn more about EE and circuits and this would be a great first project.

I was inspired by this link. The author uses an Arduino to listen for a buzz pulse sequence which will in turn open the front door by grounding the unlock circuit.

I'd like to first learn how to complete the 'Open Door' button circuit as soon as my apartment is buzzed (once I understand how this works I'll undo it obviously!) and then afterwards I'd like learn how to hook up an Arduino to open when I send a sequence of buzzes to my apartment (e.g. LONG LONG SHORT)

The wiring diagram for my handset is here. Terminal D is 'Call' and Terminal A is 'Lock'.

Project 1: Figure out how to trigger Terminal A (unlock door) when Terminal D fires
Project 2: Hook up Terminal D to my Arduino to trigger Terminal A (unlock door) when a set of conditions are passed.

I'm a complete EE newb and not quite sure where to start. Should I get a multimeter and measure what the unlock button is doing and then wire the 'call' wire to a transistor to then trigger the unlock circuit?

My apologies if my description is cringeworthy and completely wrong.
I'm not looking for someone to hold my hand here but I would really appreciate being pointed in the right direction!

 

This is the circuit diagram of the 'Open Door' button

 

View attachment 116693
This is the circuit diagram of the 'Open Door' button

Then it would appear you just need to add a NO relay contact across the C2 and P2 connections.
The relay is controlled by your Arduino or other control circuit and when the relay contacts close, the door should open.

 

Then it would appear you just need to add a NO relay contact across the C2 and P2 connections.
The relay is controlled by your Arduino or other control circuit and when the relay contacts close, the door should open.

Thanks so much for your reply! I really appreciate it.
For my Project 1 above, would a simple relay like this work? http://www.maplin.co.uk/p/24v-dc-10a-spdt-pcb-relay-n06ee

 

For my Project 1 above, would a simple relay like this work? http://www.maplin.co.uk/p/24v-dc-10a-spdt-pcb-relay-n06ee

That would work but it requires 24Vdc to operate.
You likely want one that will operate from your circuit supply voltage, such as these 5V units.
Those can still switch the 24Vdc load.