Lab 01: Blink the Onboard LED

Before you build a clock, make sure the brain of the clock is working. The Pico has a tiny green light built onto the board, next to the USB plug. It is an LED (short for light-emitting diode), a part that glows when power flows through it. This program makes it blink once a second.

The program uses nothing else in the kit: no screen, no knob, not even the kit's other files. So if this lab works, you know the Pico, the USB cable, and MicroPython are all fine.

Welcome to Lab 01

A clock is a machine that ticks at a steady beat, and today you make your first tick. One blink each second, from a program you ran yourself, on a real computer chip. Let's make time tick!

What You Will Learn

• how to run a program on the Pico from Thonny
• how to switch a light on and off from code
• how a loop makes code repeat, here forever

Run It

1. Plug the Pico into your computer with the USB cable.
2. Open 01-blink-onboard-led.py in Thonny.
3. Click the green Run button.
4. Watch the light: half a second on, half a second off.
5. Look at the shell, the text area at the bottom of Thonny's window. The program prints the line below.
6. Click the red Stop button.

01-blink-onboard-led.py v1.0

Setting Up the Light

The file begins with comments: lines that start with #, which Python skips. After them comes the first part of the program:

NAME = "01-blink-onboard-led.py"
VERSION = "1.0"
print("{} v{}".format(NAME, VERSION))

from machine import Pin
from time import sleep

led = Pin("LED", Pin.OUT)

• The first three lines print the program's name and version. Every lab in this kit starts this way, so you can always tell which program is running.
• from machine import Pin borrows the Pin tool. A pin is one of the Pico's connection points.
• from time import sleep borrows sleep, which makes the program wait.
• led = Pin("LED", Pin.OUT) gives the light a name, led. Pin.OUT means the Pico sends power out through this pin.

Why "LED" and not a number?

On a plain Pico, the light is on pin number 25. On a Pico 2 W, it is wired to the WiFi chip instead, so Pin(25) cannot reach it. The name "LED" works on every Pico board.

A Loop That Never Stops

Here is the rest of the program:

while True:
    led.on()
    sleep(0.5)
    led.off()
    sleep(0.5)

• while True: starts the loop. Everything indented under it runs again and again, like a song set to repeat. True is always true, so the loop never ends.
• led.on() switches the light on.
• sleep(0.5) waits half a second, with the light still on.
• led.off() switches the light off, and the last line waits again.

One trip around the loop takes 0.5 + 0.5 = 1 second, like the tick of a clock.

You met while True loops in chapter 10 of Learning Python. The Blink lesson in Learning MicroPython blinks a Pico's onboard light the same way.

Try This

1. Change both sleep(0.5) lines to sleep(0.1). How many times does the light blink in one second now?
2. Make a lighthouse. Use sleep(0.05) after led.on() and sleep(2) after led.off().
3. Use one small number in both sleep lines: 0.05, then 0.02, then 0.005. When do your eyes stop seeing the blinks?

If It Doesn't Work

• Nothing happens when you click Run. Look in the bottom-right corner of Thonny's window for "MicroPython (Raspberry Pi Pico)". If it is missing, unplug the USB cable and plug it back in, or try another cable.
• The program runs, but the light stays dark. The Pico may have the wrong MicroPython on it. This board needs the one made for the Pico 2 W. See Before You Start.

Your First Tick!

You switched a real light with led.on() and led.off(), and kept it going with a while True loop. Every clock face in this kit runs inside a loop like that. Next, you will give the kit a checkup.

Next: Lab 02: Kit Checkup