OpenSprinkler › Forums › Hardware Questions › OpenSprinkler › Query with the firmware driving of the DC board › Reply To: Query with the firmware driving of the DC board
Ah, I know what happened — and this is admittedly my fault not updating the part number properly. So QB1 and QB2 originally were MMBT3904 NPN transistors, and as such they should have base resistors (anywhere between 1K to 10K should be ok). However, in the end I decided to minimize the number of different parts so these were replaced by AO3400 N-channel MOSFETs, since the board already uses AO3400. As is there is now only a 10K pull-down resistor between gate and source, there is no more base resistor. So if you used MMBT3904 then it would have no base resistor causing large current draw. I think this is probably what happened. I am sorry about the inconsistency in the schematic and I will update it in github shortly.