Bypass a push button as a power supply

Hi everyone,
My name is Yaer. I am a medical student in France. I've been using arduino for a year now.

I hope you guys can help me with my project. I've recently moved in a new appartement wich is not equiped with a doorphone. I live in the first floor so it's not a big deal. My friends call on my cellphone and i go open to them.

But then i decided to resolve the problem. I've built a remote control (using an arduino, a 433mhz transmitter and a relay) and thought of placing it behind the door's electromagnet. The tests worked fine at home. There's just one thing i haven't predicted: opening the door mechanism was quite difficult. So I tried to place it behind the push button of the door. Access is easy. But supplying my device is detected as a button push. (I was stupid not thinking of this! :stuck_out_tongue: )

So my question is the following:

Is there a solution to cheat the logic level detection or do I have to open the door mechanism?

I'm using an arduino pro mini.
The button is supplied with 12v.

Thanks everyone!

Not real clear what you are trying to describe. However maybe you just need a simple relay that the arduino turns on and off and the relay contacts are wired across the two terminals of the switch that presently opens your door. Does that help?

http://www.ebay.com/itm/New-1-Channel-H-L-Level-Triger-Optocoupler-Relay-Module-for-Arduino-5V-/221409246814?pt=LH_DefaultDomain_0&hash=item338d04fe5e

Hi,
Thanks for your fast reply but it doesn’t realy help. I’m sorry I’m not clear. My english may be bad. I’ve draw some schems in paint to explain myself.

This one is doable, but the mechanism of the electromagnet is hard to access.

This one is what I hope I can do. But I don’t know how to supply power to my arduino without triggering the logic level detection of the push button.
From my point of view, the second option is just impossible. I post my problem here to see if there was a way i didn’t think of. I thought of using a battery but opening the button system every week is not easy. I would prefer the first option.

So If someone find a way to make the arduino “invisible” please let me know.

Thanks for your help, and sorry again for the poor english.

If I understand you correctly, you’ve got a door release switch which pulls a 12V signal down to ground, and you want to use the 12V signal to power an Arduino.

How much current can you draw from the incoming 12V line before it is detected as a button press, and what is the supply voltage at that point?

Yes that is exactly what I'm trying to do.
Just to make it clear to me, is it a voltage drop that is detected as a signal, or some current thing ? (I'm not very intuitive with current...) I was thinking of placing a 12v battery with potentiometer backward to the electric flow in order to test the signal limit. Will this do? Is there a more precise way?