Lab 1: Hello World with Thonny

Time: ~30 minutes | Prerequisites: none | Hardware: Raspberry Pi Pico 2, USB cable

Time to transform!

Hi, I'm Echo. Every superpower starts somewhere unglamorous, and ours starts here: making a $5 chip say hello. Thirty-four labs from now this same chip will be analysing sound in real time. Let's tune in.

What You'll Build

You'll connect a Raspberry Pi Pico 2 to your computer, open a program called Thonny, and make the chip print a message back to you. Then you'll save a program onto the chip so it belongs to the board, not to your laptop.

That's it. No wiring, no soldering, nothing to break.

Learning Objectives

By the end of this lab you will be able to:

• Describe what MicroPython is and how it differs from the Python on your laptop
• Connect to a Pico 2 from Thonny over USB
• Execute code two ways: interactively and as a saved script
• Explain the difference between a program on your computer and one on the device
• Stop a running program deliberately

Concepts Introduced

ID	Concept
201	Thonny IDE
202	MicroPython Firmware
203	USB Serial Connection
204	REPL
205	Print Statement
206	Script Execution
207	Saving To Device
208	Device Filesystem
209	Keyboard Interrupt
210	MicroPython vs CPython

Background

A microcontroller is a whole computer on one chip — processor, memory, and pins that connect to the physical world. The Pico 2 costs about $5 and is roughly as powerful as a desktop PC from the mid-1990s. That turns out to be plenty.

Normally you'd program one in C, which means compilers, linkers, and a lot of ceremony. MicroPython is a version of Python that runs on the chip itself, so you can type a line and watch it happen. Same language you may already know, running somewhere surprising.

MicroPython isn't quite Python

MicroPython is Python 3 with the heavy bits removed to fit in a few hundred kilobytes. You get for, while, functions, classes, import — all the good stuff. You don't get the giant standard library. No pandas here. That's a feature: what's left is fast and fits.

Procedure

Step 1 — Install Thonny

Download from thonny.org and install it. It's free, it's small, and it was built for exactly this.

Step 2 — Put MicroPython on the board

Your Pico 2 may arrive blank. To load MicroPython:

1. Unplug the Pico 2.
2. Hold down the BOOTSEL button (the little white button on the board).
3. While still holding it, plug the USB cable into your computer.
4. Release. A new drive appears, named RP2350.

Now in Thonny: Tools → Options → Interpreter, choose MicroPython (Raspberry Pi Pico), then click Install or update MicroPython at the bottom right. Pick the Pico 2 variant and install.

Pico 2, not Pico 1

Make sure you install the firmware for the Pico 2 / RP2350, not the original Pico. They look nearly identical and the wrong firmware simply won't boot. Later on this distinction gets very important — the older chip is missing hardware we're going to depend on. (Foreshadowing! See Lab 28.)

Step 3 — Say hello, interactively

At the bottom of Thonny is the Shell panel. That's the REPL — Read, Evaluate, Print, Loop. It's a live conversation with the chip.

Click into it and type:

print("Hello from a $5 computer!")

Press Enter. The chip runs that line and answers immediately.

Try a few more:

2 + 2
"signal" * 3
import sys
sys.platform

That last one should say rp2. You're talking to the actual silicon.

Step 4 — Open a real program

The REPL is great for poking around, but it forgets everything when you unplug. Programs are better.

Good news: every lab's code is already on your Pico. In Thonny, find the Files panel on the left. (If you don't see it, turn it on with View → Files.) The lower half shows Raspberry Pi Pico — that's the device's own filesystem.

Open 01-hello-world.py. Here's what's inside:

# Lab 1: Hello World
#
# Your first program on the Raspberry Pi Pico 2.
# Run it with the green Run button in Thonny, and save it to the DEVICE
# (not your computer) when Thonny asks where to put it.

import sys
import time

print("Hello from a $5 computer!")
print("This chip is a " + sys.implementation._machine + ".")

# range(1, 6) counts 1, 2, 3, 4, 5 -- it stops *before* the second number.
for i in range(1, 6):
    print("Counting:", i)
    time.sleep(0.5)          # half a second, so you can watch it happen

print("Done! Nothing exploded.")

Press the green Run button (or F5) and watch the Shell. Your program runs, counts to five, and stops.

Two filesystems, one window

The Files panel shows two places: your computer on top, the Pico underneath. A file open from the Pico stays on the Pico when you save it. A file open from your laptop doesn't exist on the chip at all. Mixing these up is the single most common way to lose twenty minutes — check the title bar if you're unsure which one you're editing.

Step 5 — Stop something on purpose

Programs that run forever are normal in embedded work — a thermostat never "finishes." You need a way to interrupt them.

Change the last part of your program to loop forever:

while True:
    print("Still here!")
    time.sleep(1)

Run it. It never stops. Now press Ctrl-C in the Shell.

That's a KeyboardInterrupt. Get comfortable with it — you'll use it in almost every lab.

Expected Output

Hello from a $5 computer!
This chip is a Raspberry Pi Pico 2.
Counting: 1
Counting: 2
Counting: 3
Counting: 4
Counting: 5
Done! Nothing exploded.

Troubleshooting

Symptom	Likely cause	Fix
No device in Thonny's interpreter list	Cable is charge-only	Swap for a cable that carries data — this is the #1 problem
RP2350 drive never appears	BOOTSEL not held while plugging in	Unplug, hold the button first, then plug in
Shell shows nothing at all	Wrong interpreter selected	Tools → Options → Interpreter → MicroPython (Raspberry Pi Pico)
"Device is busy"	A program is still running	Press Ctrl-C, or click the red Stop button
Edits vanished after unplugging	You edited the copy on your computer	Reopen the file from the Raspberry Pi Pico half of the Files panel
Files panel is missing	Panel hidden	View → Files

Challenges

1. Make it yours. Change the message and the count. Can you make it count backwards?
2. Do some math. In the REPL, ask the chip for 2 ** 100. It handles integers of any size. Now try 1 / 3 and look closely at the digits — we'll come back to that in Lab 10.
3. Explore. Type help() in the REPL, then help('modules') to see what's aboard.

Check Your Understanding

1. What's the difference between typing code in the Shell and saving it as a program?
2. Your program disappeared when you unplugged the Pico. What most likely happened?
3. What does Ctrl-C do, and why do you need it more on a microcontroller than on a laptop?
4. Name one thing MicroPython has that desktop Python doesn't, and one thing it lacks.

You're on frequency

You just ran code on a computer smaller than a stick of gum. Next lab we make it do something you can see from across the room.

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Next: Lab 2: Blink — Your First Hardware Program