Your First Program¶

Time to make the board do something. There are two ways to run code on it, and you'll use both all the time:

The Shell (REPL): type a line, and it runs immediately. Great for quick experiments.
The editor: write a whole program, then click Run.

Talk to the board in the Shell¶

Click next to the >>> in Thonny's Shell and type each line, pressing Enter after each one:

>>> print("Hello from my ESP32!")
Hello from my ESP32!
>>> 7 * 6
42

Everything you just typed ran on the ESP32, not on your computer. The board worked out the answer and sent it back over USB.

Now turn on the board's built-in LED. Most ESP32 boards have a small blue LED connected to pin 2:

>>> from machine import Pin
>>> led = Pin(2, Pin.OUT)
>>> led.on()
>>> led.off()

The LED turns on and off as you type. You're controlling hardware with Python!

Handy Shell shortcuts

Up brings back the previous line, so you don't have to retype it.
Tab auto-completes names: type led.o and press Tab.

Write a program in the editor¶

Typing into the Shell gets tedious for anything longer than a few lines. In the editor (the big area at the top of Thonny), type this program:

blink.py

# Blink the LED that's built into the ESP32 board (no wiring needed!)
import time
from machine import Pin

led = Pin(2, Pin.OUT)  # most ESP32 DevKit boards have an LED on GPIO 2

while True:
    led.on()
    time.sleep(1)  # wait 1 second
    led.off()
    time.sleep(1)

Click the green Run button (or press F5). Thonny asks where to save the file: choose This computer and call it blink.py. The LED starts blinking once a second.

While your program runs, the Shell has no >>>, because the board is busy. To stop it, click the red Stop button (Ctrl+F2).

What just happened?¶

Line	What it does
`import time`	Loads the `time` module so you can pause with `time.sleep()`.
`from machine import Pin`	Loads `Pin`, which is how you control the board's pins.
`led = Pin(2, Pin.OUT)`	Sets pin 2 up as an output and names it `led`.
`while True:`	Repeats the indented lines below it forever.
`led.on()` / `led.off()`	Turns pin 2's voltage on (3.3 V) or off (0 V).
`time.sleep(1)`	Waits 1 second.

Indentation matters

Python uses the spaces at the start of a line to know which lines belong to the while loop. Everything indented by 4 spaces under while True: repeats. Thonny indents automatically after a line ending in :.

Try it yourself¶

Change both time.sleep(1) lines to time.sleep(0.1). How fast can you make it blink before it looks like it's always on?
Make a heartbeat: two quick blinks, then a longer pause.

Show a heartbeat solution

import time
from machine import Pin

led = Pin(2, Pin.OUT)

while True:
    for beat in range(2):   # do this twice
        led.on()
        time.sleep(0.1)
        led.off()
        time.sleep(0.15)
    time.sleep(0.8)         # longer rest between heartbeats

Next: Saving Programs to the Board