So, I have done some experimenting. Original wiring photo attached.
- My intercom really seems to be unsupported by the Opener. The connection to the system is made by two wires. Internally there is a doorbell speaker connected by additional 2 wires and a handset connected by a structured cable. There is a simple passive opening button in the form of a spring making contact with a ground-connected contact on the board.
- Connection in the bus-intercom mode failed in all variants (Urmet bus, generic bus, both with or without doorbell suppression).
- I managed to make connection in “other door” mode shortcuting the opening button. Ok, this is a satisfactory solution.
- But I don’t give up so easy. I’d really like to have ring detection functions working. So I thought I would use the doorbell speaker for that. So I connected the yellow wire to one contact and black to the other contact of the speaker. Not detecting ring. Then I experimented with using different ground contacts in the device for the black. NO combination made the Opener detect the ring.
I have done some voltage measurements:
- 5.8 V between bus lines with off-hook handset and 9,5 V with hung-up handset
- the same voltages between open button and ground
- 4,8 V between the speaker and ground when no ring
- 0 V between the two contacts of the speaker when no ring
- about 4 V between the two contacts of the speaker when door bell rings
I’m no electrician and most probably I was making stupid iterations. But is my idea in principle correct? Can the speaker connection in general be used for the ring detection and “only” software limitation of the Opener makes it fail?