A slot machine that fits in your hand. Print five parts, click in an ESP32-C6 screen, and pull a real lever to spin three neon reels. Along the way you learn how a computer picks random numbers and decides who wins.
| Qty | Part | Type |
|---|---|---|
| 1 |
Waveshare ESP32-C6-LCD-1.47 board
The brain and the screen in one board. 1.47-inch colour LCD, USB-C, and a tiny BOOT button that the lever presses.
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electronics |
| 5 |
Printed parts
Cabinet, bezel, lever arm, ball knob and wedge foot. All five are in the 3MF below, already split onto three colour plates.
|
printed |
| 1 |
USB-C data cable
Powers the board and loads the program. It must be a data cable, not a charge-only one.
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electronics |
| 25 g |
PLA filament in three colours
Black for the cabinet, gold for the bezel, red (or any fun colour) for the ball and foot. Any PLA works.
|
consumable |
| 1 |
Chrome or Edge browser
Loads the program onto the board straight from this page. Nothing to install.
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| 1 |
Arduino IDE (optional)
Only needed if you want to change the code later. See 'Level up' at the end.
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Flash writes a precompiled image over USB-C in Chrome or Edge. The .ino below is the source — you do not need Arduino IDE unless you want to change the sketch.
A slot machine that fits in your hand. Pull the lever and three reels spin. Match two and you win a little. Match three and coins rain down the screen.
No soldering. No wires. You print five parts, push them together, plug in one cable, and click one button on this page to load the program.
This is a toy. The credits are just a number the chip remembers. Nobody wins or loses real money. That is exactly what lets us look inside and learn how the maths works.
Pick your own colours. The photos on this page show two builds: black + green + gold, and black + gold + red. Any PLA works. The 3MF is set up for three colours but you can print it all in one.
Before you start. The printer does about 2 hours of work on its own. You do about 15 minutes of clicking parts together and 2 minutes of loading the program. No tools needed. If a notch needs cleaning up, a hobby knife helps; ask an adult for that bit.
Three plates, three colours. Start the printer, then come back for Part 2 while it works.
Grab Print-ready 3MF from Files & downloads above and open it in Bambu Studio. Using another slicer? Open the STL instead, use Split to objects, and colour the parts yourself.
Plate 1: ball + foot. Plate 2: bezel. Plate 3: cabinet + lever arm. Settings are already in the file: 0.2 mm layers, 2 walls, 15% infill. The cabinet prints with supports only where it needs them.
Snap off any support inside the cabinet's top pocket. Look at the corners of the bezel: the little notches must be clear, because the board's buttons and the lever arm go through them.
No glue, no screws. Everything pushes together. If a part feels tight, wiggle it; never force it.
Screen facing out, USB-C port on the side with the gap. Press the edges down until the board sits flat. The two tiny buttons (BOOT and RESET) poke into the notches at the corners.
The bezel slides into the pocket on top of the cabinet. The screen faces the same way as the 777.
Press the ball onto the long end of the lever arm. Then push the short end into the slot at the top of the bezel, right over the BOOT button. This is the trick: pulling the lever presses BOOT for you.
Give it a gentle pull. You should feel a tiny click from the button underneath. No click? Push the arm in a little further.
Push the wedge into the slot on the bottom of the cabinet. Now it stands on your desk tilted back, like a real machine.
The board arrives empty. You are going to copy the slot-machine program onto it from this web page. That takes about a minute.
Word to know: flash. Flashing means copying a program onto a chip. The chip keeps it even when unplugged, like saving a game.
Connect the USB-C cable from the board to a computer (Windows, Mac, Chromebook or Linux). Remember: a data cable, not a charge-only one.
Scroll up to Files & downloads and click Flash to board. Use Chrome or Edge. Pick the port that appears, click Install, and wait for the green tick.
The screen lights up with three reels and CREDITS 24. If it stays black, press the tiny RESET button once.
No port in the list? Hold BOOT, tap RESET, let go of BOOT, then click Flash again. On a Mac the port is usually called usbmodem. Phones and Safari can't flash; use a computer.
Four things to try, in order.
One credit goes in, three reels spin, and they stop one after another. Watch the bottom of the screen: the words tell you what happened.
Hold for about one second. The machine changes outfit: Vegas (purple), Diner (red) and Neon (teal). It remembers your pick even after you unplug it.
+3 credits. A green banner shouts something like CHA-CHING or LADY LUCK. Miss, and a red one says SO CLOSE.
+24 credits, or +77 for 7-7-7. Coins rain down the screen and the tiny light on the back of the board goes rainbow.
Three sevens. Coins. Rainbow light.
| What you hit | Prize |
|---|---|
| Every pull costs | 1 credit |
| Any two the same | +3 |
| Any three the same | +24 |
| 7 · 7 · 7 | +77 |
You start with 24 credits. The chip remembers your score when you unplug it.
You don't need to read the whole program (it's in Files & downloads if you're curious). Each lesson below shows the one small piece of code that does the job, and gives you something to try.
Each reel has 7 symbols: 7, BAR, STAR, GEM, CHERRY, BELL, LEMON. When you pull, the chip asks for a random number from 0 to 6 for each reel. That number is the symbol.
How many different results are there? 7 × 7 × 7 = 343. Only one of them is 7-7-7. So on a fair machine you'd expect the big one about once every 343 pulls.
// One line per reel. random(0, 7) gives 0, 1, 2, 3, 4, 5 or 6.
for (int i = 0; i < N_REEL; i++) {
g_stop[i] = random(0, N_SYM); // N_SYM is 7
}From pull(). The three numbers in g_stop are where the reels will land.
Try it: pull 20 times and count how often any two reels match. About 7 or 8 out of 20 is normal. That's roughly 39%, and you can work it out: 133 of the 343 results have a match.
Every prize in the game comes from five numbers at the top of the program. Change one, flash again, and the whole game changes. That's what #define does: it gives a number a name, so you only have to change it in one place.
#define START_CREDITS 24 // what you begin with
#define SPIN_COST 1 // every pull costs this
#define PAIR_PAY 3 // two matching
#define TRIPLE_PAY 24 // three matching
#define SEVEN_PAY 77 // 7-7-7Maths corner. This machine is generous on purpose. On average each pull gives back about 1.75 credits for the 1 it costs, so your pile grows. Set PAIR_PAY to 1 and it becomes almost exactly fair: about 1.01 back per pull. Real casinos pay back less than 1. That gap is called the house edge.
When the reels stop, the program has three numbers: a, b and c. It asks two questions, in order. That's an if / else, the most useful idea in all of programming.
bool triple = (a == b && b == c); // all three the same?
bool pair = (a == b || b == c || a == c); // any two the same?
if (triple) {
win = (a == SYM_SEVEN) ? SEVEN_PAY : TRIPLE_PAY;
} else if (pair) {
win = PAIR_PAY;
} else {
win = 0; // better luck next time
}Simplified from finishSpin(). && means AND, || means OR, == means 'is equal to'.
Try it on paper: the reels show BELL, BELL, LEMON. Is triple true or false? Is pair? What's the prize? (False, true, +3.)
The lever only presses one button. So how does the machine know a pull from a hold? It uses a stopwatch. When BOOT goes down, the program writes down the time. If the button is still down 700 milliseconds later, that's a hold: change the cabinet. If it comes back up sooner, that's a pull: spin.
#define BOOT_LONG_MS 700 // 0.7 seconds
if (down && !g_bootDown) g_bootDownAt = now; // button just went down
if (down && (now - g_bootDownAt) >= BOOT_LONG_MS) // still down after 0.7 s?
cycleTheme(); // that's a hold
if (!down && g_bootDown && !g_bootLong) pull(); // let go early? that's a pullSimplified from pollBoot(). millis() is the stopwatch: milliseconds since the board turned on.
Try it: change 700 to 300, flash again, and feel how twitchy the lever gets. Then try 1500. Which feels right to you?
A program that animates can't just stop and wait. Instead it remembers what mood it's in and checks it 30 times a second. Programmers call this a state machine.
IDLE → pull → SPIN → reels stop → WIN, LOSE or JACKPOT → a moment later → back to IDLE.
Every mood draws different words at the bottom of the screen and picks a different colour for the light.
enum Phase { PH_IDLE, PH_SPIN, PH_WIN, PH_JACKPOT, PH_LOSE, PH_BROKE };
if (g_phase == PH_SPIN) setLed(220, 220, 220); // white while spinning
else if (g_phase == PH_JACKPOT) rainbow(); // party
else if (g_phase == PH_WIN) setLed(40, 220, 88); // green
else if (g_phase == PH_LOSE) setLed(90, 16, 16); // dim redSimplified from pulseLed(). setLed takes red, green and blue from 0 to 255.
Why doesn't it flicker? The program draws the whole picture into memory first, then copies it to the screen in one go, like finishing a drawing before you hold it up. Each reel is drawn inside its own little box, so symbols can't spill over the edges of the window.
Your computer can chat with the board through the same USB-C cable. That chat is called serial. Open the Serial Monitor in Arduino IDE (or any serial app) at 115200, type a word, press Enter.
| Type this | What happens |
|---|---|
help |
lists every command |
status |
shows credits, theme and what the reels say |
spin |
pulls the lever for you |
theme cyber |
jumps straight to a cabinet: vegas, diner or cyber |
credits 24 |
sets your credits |
jackpot |
forces 7-7-7 (great for filming) |
Out of credits? The screen says INSERT COIN. Type credits 24 in the Serial Monitor and you're back in business. The machine is random, so there is no trick to winning; that's the whole point of Lesson 1.
Ready to make it yours? Download lucky-slab.ino and c6_slab_pins.h, put them in a folder called lucky-slab, and open the .ino in Arduino IDE. Change the include line near the top to #include "c6_slab_pins.h". Board: ESP32C6 Dev Module, USB CDC On Boot: Enabled. Libraries: GFX Library for Arduino and Adafruit NeoPixel.
Ideas, easiest first:
PAIR_PAY and watch how fast your credits grow.WIN_LINES and LOSE_LINES to your own.N_COIN from 14 to 40 for a bigger coin storm.THEMES, pick six colours, and add a name before TH_COUNT in the ThemeId list.// id, title, background, panel, gold, ink, accent, dim
{"vegas", "LUCKY", {18, 6, 28}, {42, 12, 58}, {255, 196, 64}, {255, 236, 190}, {255, 64, 160}, {90, 40, 110}},One cabinet is one line. Every colour is {red, green, blue} from 0 to 255.
credits 24 in the Serial Monitor.
Licensed under CC BY-SA 4.0. Check with the author before commercial use.
Flash firmware
