In Boxer and Domovoy RS485 devices and the Secret Mini panel, you can use an imitation of a subscriber handset. This is a 50 Ohm resistor connected in series with a diode and connected instead of a headset, for example:
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0.25 W, 51 Ohm, Carbon resistor, Taiwan (chipdip.ru)●
1N4001, Rectifier diode 1A 50V [DO-41] (chipdip.ru)The polarity needs to be clarified on the website of the manufacturer of the switching units.
If you do not need to connect headsets in the entire building (then a switching unit is not required), you need to connect + to LINE, – to GND.
The maximum number of apartments supported by the white list is limited by the number of apartments supported by the analog panel