Hello all, I am brand new to this space. I am building a simple circuit that senses moisture through a capacitive moisture sensor, and based on a reading turns on a pump to pump water and increase the moisture level. The complication is I want to expand the pump set-up to include 4 different pumps driven by 4 different moisture sensors. Ideally, the setup would be completely battery powered (both the pi pico and the pumps) so it would not need to be connected to a wall outlet. I am struggling with how to set up this system from a power perspective, as the pumps and relay board seem to be tripping the pico, causing it to error and turn off/restart.
What is the best way to wire, and power remotely, the 4 motor setup above? Thank you for your help.
There have been volumes written about driving 5V relays with 3.3V so will not go into it here.
As for your immediate problemsm. The Pico will drive the 3.3V logic. Which in turn will switch the relays.
I think I am correct in saying the Pico WILL NOT directly drive the relays and certainly WILL NOT directly drive any pump. These have to be separately powered although could be the same actual supply.
If you can find a relay module that is fitted with 3V relays these will be OK at 3.3V but NOT directly from the Pico I/O. Some of these units have provision to power the relays separately. Use one of these and you can power from external 5V. Or I think some have 12V relays. The same applies.
The pumps. That is up to you. If you are going to power from 5V it makes sense to have 5V pumps if suitable ones are available. Some of the greenhouse systems seen on this forum in the past have been 24VAC. That does not matter as this bit is being switched by a relay.
Power requirement. This depends on the current each component requires. Add everything up. Consider worst case, that is all 4 pumps being on at the same time. Add about 50% for headroom. Then you can start considering exactly what you need to power all this.
There is NO short cut to all of this.
Try to do it with minimal up or down voltage conversion as each time you convert you lose something like 15% of your power.
Cheers Bob
As Bob mentioned, the Pico’s 3.3V output will be enough to switch the relay contacts, the 5V VBUS pin on a Pico will be fine for powering a relay module itself while it is plugged to a USB connection.
Depending on how you’re powering the Pico you may be causing a voltage drop by having all 4 relay channels going at once, do you get the same issue if you’re only running say one or two of the relays at once?
Like I said there have been volumes written on operating these relays at 3.3V so I am not going to repeat now. But basically 3.3V is WELL OUTSIDE the manufacturer’s spec for this type of relay’s operation.
Of course all 4 relays and pumps could be operating at the same time. That is worst case and if you don’t consider this you are nothing short of crazy and if you insist on going in too light with power supply current requirements I will stay well and truly clear.
Cheers Bob
