Hi, I'm making a project with different devices (sensors, pumps etc) that need different voltage to works (mainly 5v/12v/24v). Actually I'm using a standard USB 5v power supply for the raspberry and an external power supply of 5v for the sensors (connected to the gpio pin with mosfet to not damage it). I'm using darlington array to connect the valves (24v), with an external power supply (24v).
Could I use a unique external power supply of 24V for everythings? ....with a step down regulator for each device.... I have calculated the ampere that I need, and its should be enough....
One more question. In my actual set up I have 2 power supply (USB and external 5v for supply sensors and MCP23s17)...all works like a charm.... I connected the MCP23s17 via mosfets N to the GPIO SPI, and I'm using the 3.3V power pin of my raspberry to connect it.
I have try to power the 3.3v line of the N mosfet providing the current (regulated to 3.3v) from the 5v external power supply, instead of using the 3.3v pin of raspberry....Doesn't works at all..... Could you explain me why?