How to use a Potentiometer with Raspberry PI Pico (MicroPython)

Last Updated on 23rd September 2023 by peppe8o

This tutorial will show you how to use a potentiometer with a Raspberry PI Pico microcontroller. This will show you how to arrange the wirings for a simple connection and how to prepare a MicroPython code to use it.

What is a Potentiometer

A potentiometer is an electronic component including a knob used to manually increase or decrease a resistance into a circuit.

It has 3 terminals, connected with a resistive element. The 2 outer PINs should be connected to ground and Vcc, while the intermediate PIN outputs a voltage value depending on the knob position.

The 2 external PINs can be exchanged, in the sense that you can connect Ground and Vcc in one verse or the opposite one. But, the output will change complementing the Vcc value. Let me explain this with an example.

Let’s suppose that you have connected a 3,3V Vcc and ground at the outer PINs. You move the knob to a position so that you have an output of 2 V. Then, leaving the knob fixed, you exchange the Vcc PIN with the GND. Your new output will result equal to 1,3 V (that is 3,3 V – 2V).

Potentiometers are usually employed to control volume in audio systems, as well as to adjust tone settings.

Linear and Logarithmic Potentiometers

There are 2 common types of potentiometers: linear and logarithmic.

A linear potentiometer has a resistance increasing linearly on the knob rotation. This means that if you place the knob in the mid of its rotation, it will output exactly half of the Vcc value. You can identify linear potentiometers by the “B” letter printed on its label:

The label highlighted in the picture identifies a linear potentiometer with a max 10kOhm resistance.

A logarithmic potentiometer, on the other hand, has a resistance which not varies linearly, according to a logarithmic scale. These potentiometers can appear similar to the linear ones, but they are marked with an “A” label, near the potentiometer resistance.

What We Need

As usual, I suggest adding from now to your favourite e-commerce shopping cart all the needed hardware, so that at the end you will be able to evaluate overall costs and decide if to continue with the project or remove them from the shopping cart. So, hardware will be only:

• Raspberry PI Pico microcontroller (with a common micro USB cable)
• potentiometer
• breadboard (optional)
• dupont wirings

Step-by-Step Procedure

For this tutorial, I’m going to show you how to perform a simple potentiometer usage by reading its value. We’ll connect the potentiometer output to an analog port of Raspberry PI Pico, so that we’ll read the resulting values estimating the result both in analog value, in Volt, and percentage.

Wiring Diagram for Potentiometer with Raspberry PI Pico

Please arrange the wiring as shown in the following picture, according to Raspberry PI Pico Pinout. Please note that the Vcc connects the 3V3(output) PIN:

Please find below some pictures from my small lab:

Install MicroPython on Raspberry PI Pico

Connect your Raspberry PI Pico to Thonny and install MicroPython. For the very first steps and to install MicroPython, you can refer to my tutorial about the First steps with Raspberry PI Pico.

Get the MictoPython Code for Potentiometer

Please download the following MicroPython script from my download area:

pico_potentiometer.py

The following lines will explain the code line by line.

At the beginning, the script imports the required modules. the sleep function will just allow us to reduce the number of readings to 1 per second, in order to make the result readable from the Thonny shell (or it will scroll too fast).

from machine import ADC
from time import sleep

We’ve used the Raspberry PI Pico PIN 26, which is the ADC0 port. It’s a good practice to set the port number to a specific variable (for better code clarity) and then initialize the ADC object:

pot_pin = 26
pot = ADC(pot_pin)

This code reads the potentiometer output inside an infinite loop (“while True:”). In every loop, our Raspberry PI Pico reads its value with the read_u16 function. Please remember that it will return a result between 0 and 65535 (which is a range with 2 elevated to 16 values starting from zero).

while True:
    pot_value = pot.read_u16()

As we provided a Vcc of 3,3V, our result will be always inside the 0V-3,3V. The following code line maps the result in this range. The next line calculates the percentage with the same logic:

    volt = round((3.3/65535)*pot_value,2)
    percent = int(pot_value/65535*100)

The last code line simply prints the results and the “sleep(1)” adds a second of delay to make it possible for you to read the results.

    print("Volt: "+str(volt)+" | Read value: "+str(pot_value)+" | percent: "+str(percent)+"%")
    sleep(1)

Running the pico_potentiometer.py Script

Run this script in your Thonny IDE (F5) and you will start reading the output from the potentiometer in absolute values. Voltage values, and percentage values. By rotating the potentiometer knob, you will see these values changing, like in the following shell excerpt:

>>> %Run -c $EDITOR_CONTENT
Volt: 0.02 | Read value: 352 | percent: 0%
Volt: 0.02 | Read value: 336 | percent: 0%
Volt: 0.44 | Read value: 8706 | percent: 13%
Volt: 1.15 | Read value: 22869 | percent: 34%
Volt: 1.91 | Read value: 37865 | percent: 57%
Volt: 3.07 | Read value: 60942 | percent: 92%
Volt: 3.29 | Read value: 65295 | percent: 99%
Volt: 2.76 | Read value: 54829 | percent: 83%
Volt: 2.03 | Read value: 40393 | percent: 61%
Volt: 1.63 | Read value: 32295 | percent: 49%
Volt: 1.28 | Read value: 25478 | percent: 38%
Volt: 1.03 | Read value: 20356 | percent: 31%
Volt: 1.35 | Read value: 26806 | percent: 40%
Volt: 1.35 | Read value: 26886 | percent: 41%

What’s Next

Interested in doing more with your Raspberry PI Pico? Try to look at my Raspberry PI Pico tutorials for useful and funny projects!

Enjoy!