Lab 2: Blink — Your First Hardware Program

Time: ~30 minutes | Prerequisites: Lab 1 | Hardware: Pico 2, USB cable

Let's make something happen in the real world

Last lab your chip talked to your screen. This lab it moves electrons — flipping a real voltage on a real wire, half a volt at a time. That's the door into everything else we do. Time to transform!

What You'll Build

A blinking LED. Yes, really. But stay with me: the moment your code changes a voltage on a pin is the moment a program stops being abstract. Every sensor, every display, every microphone in this course is that same idea with more wires.

Learning Objectives

• Explain what a GPIO pin is and what "output mode" means
• Control a physical LED from Python
• Use time.sleep() to control timing
• Write a loop that runs forever and stop it cleanly
• Predict what happens when you change the delay

Concepts Introduced

ID	Concept
211	General Purpose IO
212	GPIO Pin
213	Pin Object
214	Digital Output
215	Onboard LED
216	Logic High And Low
217	Pin Toggle
218	Sleep Delay
219	Infinite Loop

Background

Look at the edges of your Pico 2. Those metal contacts are GPIO pins — General Purpose Input/Output. "General purpose" means the chip doesn't care what you plug in; you decide whether each pin reads the world or drives it.

A pin in output mode has exactly two states:

Value	Voltage	Nickname
1	3.3 V	HIGH
0	0 V	LOW

That's the whole vocabulary. Everything else — displays, microphones, motors — is built by flipping pins like these very fast in agreed-upon patterns.

Your board has an LED already wired to GPIO 25, so you can blink without touching a breadboard.

Digital means exactly two choices

A digital pin is on or off. Nothing in between. That sounds limiting until you realise the microphone in Lab 7 sends audio down a single digital wire — by flipping it millions of times a second. Speed turns two choices into infinite detail.

Procedure

Step 1 — Blink

Open 02-blink.py from the Raspberry Pi Pico side of Thonny's Files panel:

# Lab 2: Blink
#
# The "hello world" of hardware. If this works, your board is alive and you
# can control the physical world from Python.

from machine import Pin
import time

# Where is the onboard LED? It depends on which board you have:
#
#   Pico 2    -> GPIO 25, an ordinary pin
#   Pico 2 W  -> not a GPIO at all. The wireless chip drives it, and
#                MicroPython exposes it under the name "LED".
#
# Asking for Pin(25) on a W board succeeds but lights nothing, which is a
# nasty way to lose an afternoon. So we ask for "LED" first and fall back.
try:
    led = Pin("LED", Pin.OUT)      # Pico 2 W and other wireless boards
except (ValueError, TypeError):
    led = Pin(25, Pin.OUT)         # plain Pico 2

# Pin.OUT means "I want to drive this pin", not "read it".

print("Blinking! Press Ctrl-C to stop.")

try:
    while True:
        led.value(1)         # 1 = on  (3.3 volts on the pin)
        time.sleep(0.5)
        led.value(0)         # 0 = off (0 volts)
        time.sleep(0.5)

except KeyboardInterrupt:
    # Ctrl-C lands here. Always leave the hardware in a tidy state.
    led.value(0)
    print("Stopped. LED off.")

Run it. The little green LED next to the USB connector starts flashing, once per second.

Press Ctrl-C to stop. Notice the LED ends up off — that's the except KeyboardInterrupt block doing its job.

Pico 2 or Pico 2 W? The LED moved

On a plain Pico 2 the onboard LED is GPIO 25. On a Pico 2 W it isn't a GPIO at all — the wireless chip drives it, and you reach it by the name "LED". The sneaky part: Pin(25) is accepted on a W board and simply lights nothing. No error, no blink, no clue. The code above tries "LED" first and falls back, so it works on both.

Step 2 — Predict, then measure

Before you change anything, write down your answer:

Prediction: if you change both time.sleep(0.5) calls to time.sleep(0.05), what will you see?

Now do it. Were you right?

Try 0.005 as well. At some point your eye stops seeing a blink and starts seeing a dim, steady glow. That's not the LED changing — it's you. Human vision blurs together anything faster than roughly 50 flashes per second.

You just discovered PWM

Blinking faster than the eye can follow, to make something look dimmer, is called Pulse Width Modulation. It's how screen brightness and motor speed control work. You found it by accident, which is the best way.

Step 3 — Toggle instead

There's a shorter way to flip a pin. Replace the two value() calls with one:

while True:
    led.toggle()
    time.sleep(0.5)

Same blink, half the code. toggle() just means "whatever you are, be the other thing."

Step 4 — Make a pattern

Try a heartbeat: two quick flashes, then a pause.

while True:
    led.value(1); time.sleep(0.1)
    led.value(0); time.sleep(0.1)
    led.value(1); time.sleep(0.1)
    led.value(0); time.sleep(0.7)

Expected Output

The onboard LED blinks steadily at one flash per second, and the Shell shows:

Blinking! Press Ctrl-C to stop.

After Ctrl-C:

Stopped. LED off.

Troubleshooting

Symptom	Likely cause	Fix
Nothing blinks, no error	You have a Pico 2 W and used Pin(25)	On W boards the LED belongs to the wireless chip: use Pin("LED", Pin.OUT). The lab code tries this automatically
Nothing blinks	Wrong pin number	On a plain Pico 2 the onboard LED is GPIO 25
NameError: name 'Pin' is not defined	Missing import	Add from machine import Pin at the top
LED stays on after Ctrl-C	No cleanup handler	Add the except KeyboardInterrupt block
Can't stop it	Focus isn't in the Shell	Click the Shell panel first, then Ctrl-C
LED looks dim, not blinking	Delay too short	Increase sleep() back to 0.5

Challenges

1. SOS. Blink ... --- ... in Morse code, then pause and repeat.
2. Speed ramp. Start slow and get gradually faster, then reset. Hint: use a variable for the delay and shrink it each pass.
3. Count it. Print a running count of blinks alongside the flashing. How does adding the print affect the timing? (Keep that question in mind — it comes back with a vengeance in Lab 26.)

Check Your Understanding

1. What two voltages can a digital output pin produce on the Pico 2?
2. Why does the program need try / except KeyboardInterrupt?
3. If you deleted both time.sleep() calls, what would the LED look like — and why?
4. What's the difference between led.value(1) and led.toggle()?

That's a real superpower, small as it looks

You just made software change the physical world on command. Next lab we interrogate the chip about itself — and find the numbers that will shape every optimization decision you make later.

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Next: Lab 3: Know Your Board | Previous: Lab 1