Railway Clock Kit (Mondaine-Style)

Build the clock from the Swiss railway station: a plain white face, bold black hands, and a red second hand that stops at the top of every minute while the minute hand hops.

Look closely at a Swiss station clock and you'll notice something odd. The red second hand glides around the dial, then stops at the top and waits for a moment. While it waits, the minute hand hops forward one minute. Then the red hand sets off again. It happens once every minute, and once you've seen it, you'll watch for it every time.

Your clock does the same thing, on a bright round screen, and you write every line of its code. Along the way you learn real Python, the same language used by scientists and game makers.

Ages 10 and up. No soldering. No experience needed. Under $20 in parts.

Meet Chrono

Hi, I'm Chrono! I'm a robot, and my head is the same kind of round screen you're about to program. I'll pop up in the labs to give you tips, warn you about traps, and cheer when you finish. Let's make time tick!

What Your Clock Will Do

• Look like a station clock. A white dial, twelve heavy bars, 48 small ones, tapered black hands, and a red hand with a round disc on its end.
• Glide, stop, and hop. The red hand takes 58.5 seconds to circle the dial and then waits 1.5 seconds at 12. The minute hand moves during the wait, with a smooth start and a soft landing.
• Set its own time. It asks the internet what time it is, so it is never wrong.
• Be set by hand. Three buttons set the hour and the minute when there is no WiFi.

How It Works

There are 16 short labs, numbered 00 to 15. Each lab is one program, and each one teaches a single new idea that you use in the labs after it.

1. Wake it up (labs 00-01). Blink a light and say hello on the screen.
2. Build the face (labs 02-06). Place dots, then bars, then hands, one idea at a time, until the finished face appears on the screen.
3. Make it tell time (labs 07-09). Read the Pico's clock, set it from the internet, and make the red hand tick.
4. Make it glide, stop, and hop (labs 10-12). The three labs that make this clock special.
5. Make it yours (labs 13-15). Test the buttons, set the time by hand, and put everything together.

Why Kids (and Grown-Ups) Like It

• You see results fast. Every lab ends with something new on the screen, not just text in a window.
• A real design. The proportions come from one of the most famous clock faces in the world, so you also learn why it looks the way it does.
• It is a real computer. The Raspberry Pi Pico W is the same kind of chip found in appliances, toys, and instruments.
• Mistakes are cheap and safe. Nothing you type can break the kit. The only thing to watch is one wire, and the kit tells you which.

For Parents

• What your child learns: Python programming (variables, loops, functions, classes), the math of angles, how a computer reads buttons and draws to a screen, and how a clock keeps time.
• How much help they need: Most 10-12 year olds do the labs on their own once the kit is set up. An adult helps most with the first-time setup (about 30 minutes).
• Privacy and safety: The clock has no microphone and no camera. It connects to your home WiFi only to get the time, and it stores nothing about your family. It runs on a 5-volt USB cable, so there is no mains wiring.
• What it costs: Under $20 in parts (a $5 Pico and a $6 display are the big two), and no subscription. The parts are the same ones as the Chrono Smart Clock Kit, so a kit you already have runs both. See Notes for Teachers for where to buy.

For Teachers, Mentors, and Volunteers

• Fits a class period. Each lab is a self-contained 30-45 minute session with a working result at the end. Labs 00-04 make a good first meeting.
• One new idea per lab. The concept list is in the Notes for Teachers: loops, math, functions, % and if, tuples, while, if / else phases, easing, and classes.
• No soldering, no special tools. Everything plugs into a breadboard.
• Runs on what you have. Any computer that runs Thonny (Windows, Mac, Chromebook, Linux) works.
• Every picture is real. The screen images come from the labs' own code running on a simulator of the display, so what students see in the book is what the code draws.

What's in the Kit

A rear view of the kit showing the breadboard, buttons and a 20cm Dupont cable with hot glue to make it easy for the student to connect the display.

Part	What it does
Raspberry Pi Pico W	The brain of the clock. It's a microcontroller, a tiny computer on a board about the size of a stick of gum. The W means it has WiFi, so it can talk to the internet. A Pico 2 W works too.
Round color display	The clock face. It is 2.1 inches across and has 360 × 360 tiny dots of light called pixels. A chip on the back called the GC9B72 turns the Pico's messages into pictures.
Three push buttons	How you control the clock. They are called MODE, UP, and DOWN.
Breadboard and wires	Connect everything without soldering.
USB cable	Gives the Pico power, and lets your computer send it programs.

How It Is Wired

The display has a row of 10 connection points along its bottom edge. Reading from left to right, they are labeled: GND VCC SCL SDA RST DC CS BL SDO TE. Only the first eight are used. Each one connects to a numbered pin on the Pico, like this:

Display pin	Pico pin	Wire color	What it carries
GND	GND	black	Ground, the "minus" side of the power
VCC	3V3	red	Power, 3.3 volts
SCL	GP2	orange	The clock beat that keeps the Pico and display in step
SDA	GP3	yellow	The data: the actual colors of the pixels
RST	GP4	green	Reset: tells the display to start fresh
DC	GP5	blue	Says whether the next data is a command or a picture
CS	GP6	purple	"Hey display, I'm talking to you!"
BL	GP7	gray	The backlight that makes the screen glow

Use 3V3, Not 5 Volts

The display's VCC wire must go to the Pico's 3V3 pin. The display is built for 3.3 volts, and 5 volts can damage it. Just a few pins away are VSYS and VBUS, which carry about 5 volts from the USB cable, so double-check the label before you plug in.

The last two pins on the row, SDO and TE, stay unconnected. The clock only ever sends pictures to the display, so it never needs them.

Each button has two legs. One leg goes to a Pico pin, and the other goes to GND:

Button	Pico pin	What it does in this kit
MODE	GP13	Steps through run, set hour, set minute. Hold it to set the clock from the internet.
UP	GP14	Moves the hand being set forward
DOWN	GP15	Moves the hand being set back

Before You Start

You only need to do these steps once.

1. Put MicroPython on the Pico. MicroPython is the version of the Python language that runs on small boards like the Pico. Be sure to use the version that matches your board, for the Pico W or the Pico 2 W. The versions for the plain Pico and Pico 2 have no WiFi.
2. Install Thonny. Thonny is the program you will use to write code and send it to the Pico.
3. Copy the kit's files onto the Pico. The labs need some helper files that live in a folder called lib on the Pico, and a settings file called config.py. Your teacher may have done this for you. If not, the kit folder has a script called upload-code.sh that copies everything at once.
4. Tell the clock about your WiFi. Copy the file secrets-template.py to a new file called secrets.py, and type in your WiFi network's name and password. Labs 08 and 15 use it. (secrets.py is kept private: it never gets shared online.)
5. Tell the clock your time zone. Open config.py and find TIMEZONE_HOURS. Use -5 for Eastern time, -6 for Central, -7 for Mountain, or -8 for Pacific.

The Labs

Click a picture to open that lab.

Lab		What you will do
00		Make a tiny light on the Pico blink, to check that everything works
01		Say hello on the round screen
02		Place twelve dots in a circle with sine and cosine
03		Draw the twelve heavy hour bars with your own functions
04		Add the 48 small minute bars with % and if
05		Turn a time into angles and draw the black hands
06		Add the red second hand, and finish the face
07		Show the Pico's real time on the face
08		Ask the internet what time it is
09		Make the red hand tick once a second
10		Make the red hand glide, in milliseconds
11		Make the red hand stop at 12 and wait
12		Hop the minute hand during the wait
13		Test the three buttons
14		Set the time with the buttons
15		Put it all together into one finished clock

Which Program Is Running?

Every lab prints its name and version number in Thonny's shell when it starts, like 12-minute-jump.py v1.0. If the screen isn't doing what you expect, check that line first. It tells you which program the Pico is actually running.

Words to Know

Word	What it means
Pixel	One tiny dot of light on the screen. This screen has 360 × 360 = 129,600 of them.
Microcontroller	A small computer built to control one thing, like a clock, a toy, or a microwave.
Program	A list of instructions for a computer, written in a language like Python.
Loop	Part of a program that repeats over and over. A clock's program runs in a loop forever.
Variable	A name that holds a value, like second = 42.
Function	A named set of instructions you can use again and again, like bar().
Module	A file of Python code that other programs can borrow from with import.
Millisecond	A thousandth of a second. The red hand is redrawn every 50 or so of them.
Easing	Making a move start slowly and end gently, instead of starting and stopping all at once.
WiFi	A way for devices to connect to the internet without wires.

About the Design

The look of this clock follows the Swiss railway station clock, designed for the Swiss Federal Railways (SBB) in the 1940s. This kit is an independent project for learning. It is not made, sold, or endorsed by SBB or by Mondaine, and the face has no logo or brand name on it. "SBB" and "Mondaine" belong to their owners.

For Teachers

The Notes for Teachers page has the technical details: the lab sequence and the idea each lab introduces, how the face is drawn without flicker, the timing of the stop-and-go, what has and hasn't been tested on real hardware, and a troubleshooting table. The screen pictures in these pages were made by running each lab's real code in a simulator of the display.