Getting started with the Raspberry Pi Pico 2 in MicroPython

Guide no. 79

From installing MicroPython to your first LED, a button, a fading light and the chip temperature, with Thonny.

By Ada Intelisano · informaticait.it technical team

Download the PDF (A4, 7 pages) Free to print and share, without changes — CC BY-ND 4.0

In short

To install MicroPython, hold down BOOTSEL and drag a .uf2 file onto the board.
Thonny sends programs to the board and shows what they print.
LED on GP15 with 220 Ω, button on GP16 with the internal resistor.
The pins work at 3.3 V; the onboard LED is called “LED”.

Time: one hourLevel: start hereYou need: a computer with Thonny

The Raspberry Pi Pico 2 costs a few euros and you program it in Python, the language many people learn at school. Nothing to compile: write a line, press a key and the board runs it right away. In an hour you will blink an LED, read a button, dim a light and measure the chip temperature.

1The parts

a Raspberry Pi Pico 2 with the pins already soldered (a Pico H works too) and a micro USB cable that also carries data;
a breadboard, a red LED, a 220 Ω resistor, a breadboard pushbutton and three jumper wires;
a computer with Thonny, a free program for writing Python.

New word: MicroPythonA version of Python made for microcontrollers. You install it on the board just once; after that you send it programs from Thonny and it runs them line by line.

2Meet the board

Forty pins, numbered 1 to 40: 1 to 20 down the left side from the top, 21 to 40 up the right side from the bottom. The GPIOs are called GP0, GP1… and work at 3.3 V. Next to the USB connector you'll find the onboard LED and the BOOTSEL button, which you'll need in a moment.

3Install MicroPython

Download the MicroPython .uf2 file for your model from micropython.org (Pico 2: “RPI_PICO2”; Pico: “rp2-pico”).
Hold down BOOTSEL and plug the USB cable into the computer, then let go of the button.
A drive shows up, like a USB stick, called RP2350 (on the Pico it's RPI-RP2). Drag the file onto it: the board restarts by itself.
In Thonny, at the bottom right, choose the interpreter “MicroPython (Raspberry Pi Pico)”.

4Your first program

Type these lines in Thonny and press the green triangle (Run).

# The first program: the LED on the board turns on and off every half second.
from machine import Pin
import time

led = Pin("LED", Pin.OUT)   # "LED" works on the Pico 2 and on the W models

while True:
    led.toggle()            # if it was on it turns off, and the other way around
    time.sleep(0.5)

✓ What you should seeThe LED next to the USB connector turns on and off every half second. Press the red button (Stop) to stop it.

New word: main.pyIf you save the program on the board as main.py (“Save as” → “MicroPython device”), it starts by itself every time the board gets power, even without a computer.

5LED and button on the breadboard

The Pico straddles the center channel, with the USB on the right.
LED: from pin 20 (GP15) through the 220 Ω resistor to the long leg of the LED; the short leg goes to the − rail.
Button: one leg to pin 21 (GP16), the other to the − rail. The two − rails go to the Pico GND pins (pins 18 and 23).

# The button turns on the red LED: when pressed, pin GP16 goes to GND and reads 0.
from machine import Pin
import time

led = Pin(15, Pin.OUT)                       # GP15, physical pin 20
# GP16, physical pin 21, with the internal resistor to 3.3 V
pulsante = Pin(16, Pin.IN, Pin.PULL_UP)

while True:
    if pulsante.value() == 0:
        led.on()
    else:
        led.off()
    time.sleep_ms(10)

✓ What you should seeHold the button down: the red LED turns on. Let go: it turns off.

New word: PULL_UPA resistor inside the chip that keeps the pin at 3.3 V while the button is open. When you press it, the pin goes to GND and reads 0. That way you don't need an extra resistor on the breadboard.

6The breathing light

PWM turns the pin on and off a thousand times a second. By changing how long it stays on, you make the LED look brighter or dimmer. In MicroPython that “how long” goes from 0 to 65535.

# The LED slowly fades on and off:
# PWM changes how much of the time the pin stays on.
from machine import Pin, PWM
import time

led = PWM(Pin(15))
led.freq(1000)                  # 1000 times a second: the eye only sees the average

while True:
    for livello in range(0, 65536, 512):     # from off (0) to fully on (65535)
        led.duty_u16(livello)
        time.sleep_ms(8)
    for livello in range(65535, -1, -512):
        led.duty_u16(livello)
        time.sleep_ms(8)

✓ What you should seeThe red LED slowly brightens and then fades out, over and over.

7The hidden thermometer

Inside the chip there is a temperature sensor, connected to channel 4 of the analog converter. The formula comes from the datasheet. It measures the chip, not the room, but touch it with a finger and you'll see the number go up.

# The thermometer inside the chip: converter channel 4 and the datasheet formula.
from machine import ADC
import time

sensore = ADC(4)
fattore = 3.3 / 65535                        # from number (0-65535) to volts

while True:
    volt = sensore.read_u16() * fattore
    gradi = 27 - (volt - 0.706) / 0.001721
    print("Chip temperature: %.1f °C" % gradi)
    time.sleep(1)

✓ What you should seeIn the bottom part of Thonny a new line appears every second, for example “Chip temperature: 26.3 °C”.

If it doesn't work

Thonny doesn't see the board: the cable is charge-only, or the interpreter isn't selected.
The external LED stays off: it's in backwards, or the resistor isn't in the same column.
No RP2350 drive: you let go of BOOTSEL too early, try again.

8Challenge yourself

Try it yourself

Make the red LED blink three times every time you press the button.
Turn on the external LED when the chip temperature goes above 30 °C.
Build the traffic light from guide no. 39 again, with three LEDs on the Pico.

✓ What you learned

you install MicroPython by dragging a .uf2 file;
pins, PWM and the ADC take just a few lines of Python;
main.py starts by itself at power-up;
the Pico pins work at 3.3 V.

Sources: Raspberry Pi, Raspberry Pi Pico 2 datasheet · Raspberry Pi, MicroPython documentation for microcontrollers and “Pico-series Python SDK” · Raspberry Pi, RP2040 and RP2350 datasheets (temperature sensor) · MicroPython, rp2 port documentation (Pin, PWM, ADC) · informaticait guides no. 34, 35, 37 and 39