Hallo,
I want show my way of presence detection. I build myself a plug board to detect if a certain key is plugged in. The plugs are standard audiojacks in which i soldered a resistor. Then I have a another resistor so I get a voltage divider and measure the analog voltage between the resistors. To read more than one jack I’m switching between the different plugs with some FETs (probably working with transistors as well, just had FETs liing arround) where every jack has its own resistor Value and therefore a different measured voltage. After measuring the voltages I send the information back to openhab via MQTT.
Greetings