OpenSprinkler › Forums › Hardware Questions › OpenSprinkler Pi (OSPi) › OSPi 12vdc – should there be a ground between COM socket and transitor ground? › Reply To: OSPi 12vdc – should there be a ground between COM socket and transitor ground?
First thing is to check the orange terminal block: on your picture, the pin on the left (closer to a row of 5 or 6 ground pins) should be ground, and the pin on the right (closer to the COM) terminal is the COM wire. So obviously these two pins (on the orange terminal clock) are NOT connected — the two sharp triangles facing each other are called PCB spark gaps, they are for releasing high voltage charges but are normally completed separated from each other.
Next, if you are using 12VDC to power the board, DC power has polarity. So make sure the negative of the power goes to the ground pin on the orange terminal block, and the positive goes to the other (i.e. COM wire).
If the power is connected correctly, the power supply’s negative pin is obviously shared with the circuit ground, and that in turn should be shared with each of your transistors’ emitter pins.