Is there an easy way to take the PWM output from a Raspberry Pi Pico W that scales from 0-3.3V DC so that it scales from 0-10V?
I have several devices that can accept a variable output voltage in the 0-10V range as a control signal, but the Pico can only push 3.3 V max.
The pump I’m trying to control won’t even turn on at 3.3V, much less scale the pump speed relative to the control voltage. So what I need is to transform the output PWM voltage from the Pi so that it ranges from 0-10V.
I’m guessing (hoping?) that there’s a board or device that doesn’t require me to solder up a circuit from scratch to do this.
Thoughts?
Edit: An analog version of what I want to do already works, but it’s too cumbersome: basically, I attach an Adafruit digipot (via I2C) to the Pi, and then attach a separate 10V VCC source to the digipot. The voltage divider on the potentiometer can then be controlled to output 0-10V.
I’m trying to avoid that, however, as I would have to have a separate digipot for each device I want to control. Also, some of the devices I’m looking at specifically say they take a 0-10V PWM input as a control signal (separate from the actual power supplied to the device).
My 2p take on this is that you’re interpreting the PWM output as an analog voltage of 0-3.3v but that’s not how it works. The PWM pin provides 3.3v pulses that vary between off - tiny spikes - fatter spikes - full on.
So all you need is a MOSFET powered from a 10v power supply supply driven by the Pico’s PWM pin that can faithfully switch 10v pulses at the same pulse-width from the Pico i.e. an amplifier. I’m sure someone can point to a simple circuit to do that (just a MOSFET and some resistors?)
Thanks for the quick response! As a low-level electronics noob, I always appreciate good advice and knowledge shares.
I do have a question, though: From what I understand with PWM, isn’t the amplitude of the square wave equal to the output voltage? So, if the amplitude is 10V, but the duty cycle is only 50%, that would average out to a relative 5V output - correct?
Or am I missing something (which is highly likely).
Edit: And, for example, the light I’m talking about says that it takes a 0-10V PWM control signal. I interpreted that to mean a 10V signal that varies the duty cycle between 0 (0V) and 100% (10V)?
Again, I’m probably getting that wrong - hence all the questions.
With PWM as it’s name implies its the pulse width - not its frequency or amplitude - that changes.
Typically used to dim LEDs which are not easy to dim by simply changing the voltage.
For a supply of 3.3v and setting to on:off -
Using a 25:75 pulse the full voltage is only present for a quarter cycle so the average voltage is 0.82v.
Using a 50:50 pulse the full voltage is only present for half a cycle so the average voltage is 1.65v.
Using a 75:25 pulse the full voltage is present for three-quarters of a cycle so the average voltage is 2.47v.
The same pulse being switched on a 10v supply would give pro-rata “voltage” output
Depending on the frequency used, a LED might visibly flash but a motor would simply “see” a lower voltage.
I think I understand - the max output voltage doesn’t vary (for a Pico, that’s 3.3V). The duty cycle determines how much of that voltage something like a motor “sees”.
So, if I want to vary the PWM voltage between 0-10V, I have to have something that either:
Supplies an initial max output voltage of 10V, or
Uses the PWM output of 0-3.3V to control another device capable of providing a variable output up to 10V.
Or, in the case of the pumps I’ve referred to, (some base value) - 4.5 V.
For a 10 volt device you will need an actual 10 (or 12) volt power supply.
Then use a motor driver circuit driven by the PWM pin that switches the motor with effectively 10v pulses.
Logistically making a high-speed on/off switch in series with the motor.
Something like this (though out of stock at Pimoroni)
