Need help with a phone controlled electronic door system I'm building

Discussion in 'The Projects Forum' started by ssankoo, May 25, 2014.

  1. ssankoo

    Thread Starter New Member

    May 25, 2014
    Hey guys!

    Recently I've started gaining more and more interest in electronics and circuits and now that I am working on a few projects I am stuck with a project. I know the basics of electronics (what components do etc) but am new to this forum.

    I live in an apartment on the first floor. When somebody comes over and rings the bell I have to walk to the door of my apartment and press a button which opens the front door of the complex for a few seconds. I want to automate this by wiring a cellphone to the 'buzzing' circuit so I can call a specific number and then the door opens normally for a few seconds without me having to physically press the button.

    The system that's in place now is a Siedle BTS 850-02 and I can remove the casing very easily. This shows 3 contacts labelled Ta, Tb and Ert (Ert is probably German for ground). I can also access the button wiring inside the phone's circuit. (the wiring for the 3 buttons up front) and the connections look something like this. Now I know that connecting the (in the previous images marked) red and blue contacts will open the door and I've tried soldering 2 seperate wires to each of these contacts but the contacts are very small and it's extremely hard to solder that perfectly.

    My idea was to use a phone (which I already have), insert a sim card (which I bought), open up the phone and somehow make use of the buzzing circuit by remove the buzzer component and using a 3.3 volt optocoupler (first I wanted to use a relay) with the now loose 2 wires to control the connection of the wires I wanted to solder to the button of the door system.

    As I said I got stuck on the soldering part because it was so hard to solder that perfectly. I also think my Optocoupler is broken, I used this one but the resistance between pin 4 and 5 stayed 1 when I measured with a multimeter when I connected it to an Arduino's 3.3V output. I am now considering using some sort of linear actuator (solonoid maybe?) to physically pressing the button but I'm not sure if this is the best way to go.

    Can you guys help me out with this or maybe give me a few tips on what I should do or look out for?

    Thanks a lot!

    I forgot I actually found this forum by google and came upon this thread. I think that person wants to accomplish partially the same thing, but that thread is almost 3 years old and I didn't find too much good information on there.
    Last edited: May 25, 2014
  2. crutschow


    Mar 14, 2008
    Show a picture of what you are trying to solder.

    How did you connect the Arduino to the opto coupler? Did you add a resistor in series with the opto input? Did you measure the opt's output resistance in both directions with the meter?
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Interesting project but methinks you will be doing just as much walking, getting up to switch the phone charger on/off ;). Anyway, I'm sure the exercise would be beneficial.
  4. ssankoo

    Thread Starter New Member

    May 25, 2014
    Thanks for taking the time to reply! Looking at this example, I connected pin 1 to the Arduino's 3.3V supply without a resistor (I thought it wasn't necessary because 3.3V is still quite low). I then connected pin 2 to ground, pin 4 to one side of the phone's buzzer and pin 5 to the other side of the phone's buzzer (and since I only need a connection, I don't think it matters which wire goes to which side). I did measure the opt's output resistance in both directions but to be sure, I'll do that again this afternoon. When I get home I'll also add a picture of what I'm trying to do.

    Again thanks for the help!
  5. ssankoo

    Thread Starter New Member

    May 25, 2014
    Haha thanks for replying, but I'm getting enough exercise as it is and the phone is a very old one, so it probably needs to be charged twice a month. I could also just leave the charger plugged :)