A photo relay coupled MOSFET
The input connector is a 3-pole, so follow the standard Thereminico which provides + 5VDC central pole. But in this circuit the +5 Volt is not used, then you can use two single cables Dupont for signal and to GND.
If you have to drive multiple forms together, you could combine the Central Server with GND, with a spot of solder on the bottom of the print. That way you could carry only one bulk cable (GND) and then use the Central Server to bring mass to neighboring modules
More info on the theremino official site: