OpenSprinkler › Forums › Hardware Questions › Alternative hardware › Re: Re: Alternative hardware
September 9, 2014 at 3:18 pm #25164
OSPi uses a 74HC595 shift register to generate 8 outputs. The shift register take 4 GPIO pins. It’s implemented this way so you can easily cascade additional shift registers to produce more outputs without using more GPIO pins (and that’s how the expansion boards work).
If you want to use 8 GPIO pins to directly drive relay board, you can use Rich Zimmerman’s sprinklers_pi program, which supports this option.