Python in the physical world · Day 1

Make it light

Today, one line of Python will leave the screen and change the real world.

Mission: send a secret message using light.

Teacher slides Press S for speaker notes · F for fullscreen

Learning goals

By the end, you can…

01

Use Thonny’s Shell and editor for two different jobs.

02

Recognise strings, integers, floats, expressions, and variables.

03

Read errors and trace a script one line at a time.

04

Explain how Python changes an LED output.

05

Build an LED circuit safely with a resistor.

06

Create a recognisable light signal using named values.

Today’s route

Teach → practise → build

Meet
Python
→
Read
code
→
Control
light
→
Build a
signal

During teaching: predict before Run. During the lab: change one thing at a time.

01

Part 1 · Your tools

Meet Python and Thonny

First understand the tools. Then use them to control hardware.

A computing system

Input → process → output

Watch and discuss · Thonny stays closed for now

Your code
input
→
MicroPython
process
→
Text + light
output

What is different about a physical output?

Our IDE

Find the Files, Editor, and Shell

Do now · Open Thonny and follow along

Real Thonny window connected to a Raspberry Pi Pico. Files on this computer and the Pico are on the left, the Python editor is upper right, the Shell is lower right, and the status bar says MicroPython Raspberry Pi Pico.

Files

Choose a saved program on this computer or the Pico.

Editor

Write, change, and save a complete program.

Shell

Try one line now and read program output or errors.

Your colours and toolbar may differ, but these three areas do the same jobs.

Interactive mode

The Shell answers one line now

Try in Thonny · Type each line after predicting


>>> print("Hello, Pico!")
Hello, Pico!
>>> 2 + 3
5
>>> type(0.5)
<class 'float'>

The interpreter reads Python, evaluates it, and shows the result.

Values and types

Python asks: “What kind of value is this?”

Discuss · Keep Thonny open, but do not type yet

string

"Pico"

Text inside quotes.

integer

42

A whole number.

float

0.5

A number with a decimal point.

Why is "42" not an integer?

Expressions

An expression produces a value

Try in Thonny · Predict, then test all three


2 + 3
10 / 2
"Pi" + "co"

Think like the interpreter

  1. Read the values.
  2. Apply the operator.
  3. Produce one result.

Predict: Which result is a float? Which is a string?

Errors are evidence

Read the last line first

Try in Thonny · Make this typo on purpose


>>> pritn("Hello")
Traceback (most recent call last):
  File "<stdin>", line 1
NameError: name 'pritn' isn't defined

1 · Name it

NameError

2 · Locate it

Line 1

3 · Compare it

pritn versus print

Change only pritn to print, then run it again. If it works, the misspelling caused the error.

02

Part 2 · Saved programs

From one line to a script

A saved program lets us plan a sequence and run it again.

Script mode

The editor stores a sequence

Try in Thonny · Type, save, predict, then Run

Shell

Runs one instruction immediately.

Best for a tiny experiment.

Script

Saves instructions in a .py file.

Runs from top to bottom.


print("Three...")
print("Two...")
print("One...")
print("Hello, physical world!")

The program is the instructions. The output is what happens when they run.

Read line by line

Trace before you press Run

Watch · Point to each line; do not run it yet


from machine import Pin
from time import sleep
led = Pin("LED", Pin.OUT)

print("Light on")
led.on()
sleep(1)
led.off()
print("Finished")

Screen

Which words appear?

Pico

When is the LED on?

Time

Where does it pause?

Hardware vocabulary

Three lines connect Python to the Pico

Try together · Open and Run 01_hello_pico.py

Pin

Gives Python access to a Pico pin.

"LED"

Names the onboard LED.

Pin.OUT

Says the pin sends a signal out.


from machine import Pin
led = Pin("LED", Pin.OUT)
led.on()

Today you may reuse this setup. Your job is to explain what it achieves, not reproduce it from memory.

Variables

A useful name that refers to a value

Discuss · Identify names and values before running


message = "Team Comet"
on_time = 0.15
off_time = 0.35

Left of =

The variable name.

Right of =

The value stored under that name.

Which variable changes text? Which variables change time?

Why names matter

One edit can change every use

Try in Thonny · Open 02_variable_blink.py and Run it once 


on_time = 0.15

led.on()
sleep(on_time)
led.off()

Experiment

Change 0.15 to 1.5.

Predict: What changes? What stays unchanged?

sleep(on_time) uses the value stored in on_time. Change that value once, and all three ON pauses change.

Comments

Notes for humans, ignored by Python

Discuss · Which comment helps a reader more?


# First group: three short flashes
led.on()
sleep(short_flash)
led.off()

Useful comment

Explains the intention: what does this block mean?

Not useful

# turn LED on merely repeats led.on().

03

Part 3 · From code to circuit

Make the physical output safe

Code can be corrected with Run. Wiring must be checked before power.

Safety gate

Unplug → build → partner-check → power

Get ready to build · Stop the program and unplug USB

Before touching wires

Stop the program and disconnect USB.

One contact per hole

Every coloured endpoint dot represents one real breadboard hole.

Use the resistor

GP15 must reach the ordinary LED through 220 Ω.

Check orientation

Long leg/anode toward the resistor; short leg/flat edge toward GND.

Never connect a GPIO directly to GND. Stop if anything becomes hot.

Ordinary LED · GP15

Follow the route, not just the colour

Exact diagram + table
Day 1 breadboard diagram: GP15 through a 220 ohm resistor to the LED anode, with the cathode connected to GND.

What ON and OFF mean

Why the LED lights

Discuss · Trace the complete circuit

led.on()
GP15 becomes 3.3 V
→
Current flows
resistor protects LED
→
LED lights
then current reaches GND
led.off()
GP15 becomes 0 V
→
No voltage difference
current stops
→
LED is dark

In the copied program, change only Pin("LED", Pin.OUT) to Pin(15, Pin.OUT).

Debugging physical systems

Code, circuit, or assumption?

Discuss · Choose one exact check for each column

Code

Wrong pin? Misspelled name? Program still running?

Circuit

LED reversed? Wire one row away? Missing resistor?

Assumption

Did we predict the wrong output or inspect the wrong LED?

If the external LED stays dark: first run the known-working onboard-LED file. If that works, run the supplied GP15 ON/OFF test. If GP15 still does not light the LED, stop, unplug USB, and check the circuit against the diagram.

04

Part 4 · Your challenge

Secret Signal Machine

Now apply the teaching. The challenge is yours; the setup is supplied.

Your build

Create a message made of light

Must include

  • a printed team name;
  • short and long flashes;
  • at least two timing variables;
  • a clear pause between groups of flashes;
  • a final off state.

Build it in this order

  1. Run the starter: check its one short flash.
  2. Add two short flashes to finish the first group.
  3. Change short_flash; check all three.
  4. Add a pause, then a group using long_flash.
  5. Hide the code and ask a partner to decode it.

Start with 03_secret_signal_starter.py. Do not open the solution until your own signal works.

Exit ticket

Complete the explanation

“When Python runs led.on(), the output is ________, and when Python runs print(), the output is ________.”

What evidence today changed how you think code works?

Day 1 complete Stop program · unplug USB · return components

Teacher reference

Teaching sequence and sources

Adapted teaching sequence

TEALS Unit 1 lessons 1.01–1.05: IDE, interpreter, values and types, expressions, scripts, variables, comments, and debugging.

Physical-computing adaptation

Thonny with MicroPython, onboard LED, GP15 ordinary LED circuit, and the Secret Signal Machine lab.

Source curriculum: TEALS Introduction to Computer Science, Unit 1 slide decks . Course circuit artwork is original and documented in the workshop source notes.