Pump PWM signal

#1

I bought two of the pumps with the PWM speed control. However, I do not entirely understand how to connect them.

I have a 24V DC power supply for the pump, and a 5V DC power supply for a Raspberri pi. I want to have the Pi output the PWM signal. But the red/black wires already connect to the 24V power supply (via a relay). Presumably the negative end of the two power supplies should be connected somehow? How do I do this?

Probably a stupid question - go easy on me please :wink:

#2

You don’t need a relay.

  • Connect Raspberry Pi GND to pump GND (black)
  • Connect Rasperry Pi output pin (PWM) to blue wire
  • Connect 24V supply + to pump red wire and - to pump black wire.

Switch the pump on and off with the digital output of the Pi, or use PWM for speed control. The pump will be off for values under 10%.

BrewBlox firmware can also send the PWM signal from the Spark.

#3

Thanks for the speedy response. So that I understand this correctly, I will effectively connect 24V - to Pi GND then?

#4

Yes. Voltage is relative. By connecting GNDs of different circuits, you ensure that they have the same reference level. So 5V in one circuit equals 5V in the other circuit.