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What kind of circuit would I have to devise in order to read a certain amount of voltage (let's say 0.5V) from my RITTO Twinbus Door Bell system with my RPi?

In detail what I want to achieve: there is a Diode flashing when somebody rings the bell and there is also a 4-legged button soldered on the board I can press to open the door. I want to control these with my RPi. I am capable of soldering and understanding physics but I have gotten a bit rusty on the details.

The alternative would be a 500 Eur+ propietery system, which I want avoid to invest in.

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So you want to read out the LED, and be able to simulate a button press?

Safest way would be to use a light sensor to read the LED, and a relay to trigger the button press.

(These units seem to be operated on 15V AC power http://en.ritto.de/uploads/tx_seqdownload/4573_System_-_Handbook_10_2001.pdf)

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  • Thanks for your reply. I read out the current from my wall for my unit (not quite the same you posted, but this system: See 7630 at ritto.de/uploads/tx_seqdownload/…) and it has 24,8V AC. Reading out the LED with a light sensor sounds like a marvellous idea. Do you have a link to some component? Could you help me to build a circuit based on that. How would I relay the button press? This does not have to be mechanical of course, but can be soldered onto the RITTO circuit where the button is fixed upon.
    – user10193
    Apr 19 '14 at 11:00
  • Since I don't know the voltages used on the board itself, the safest would be to not rely on any voltage. That is why I proposed both the light sensor and the relay. As for the relay, just connect it in parallel with the button (the button has 4 pins, but they are internally connected in 2 pairs). The led would be a bit more tricky. How bright is it? Is it okay if the led is no longer visible (removing daylight will make detecting it easier)? I'd be happy to try and make a diagram for you.
    – Gerben
    Apr 19 '14 at 15:05

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