Lesson 13 of 16

Spin a prize wheel

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#include <AccelStepper.h> const float STEPS = 2037.8864; // steps per turn: 32 steps × a 63.68:1 gearbox const int SEGMENTS = 8; const int BUTTON = 2; const int DIR = 1; // 1 = clockwise, −1 = anticlockwise // the driver's IN1-IN4 on D8-D11, given in the order 8, 10, 9, 11 so the coils fire in sequence AccelStepper wheel(AccelStepper::FULL4WIRE, 8, 10, 9, 11); const char* PRIZES[] = {"50", "100", "200", "AGAIN", "500", "x2", "1000", "JACKPOT"}; int at = 0; // the segment under the pointer now long moved = 0; // segments travelled since power-on void setup() { pinMode(BUTTON, INPUT); wheel.setMaxSpeed(15 * STEPS / 60.0); // turns per minute → steps per second wheel.setAcceleration(1200); Serial.begin(9600); randomSeed(analogRead(A0)); Serial.println("Press the button to spin the wheel!"); } void loop() { if (digitalRead(BUTTON) == HIGH) { int prize = random(SEGMENTS); int ahead = DIR > 0 ? (prize - at + SEGMENTS) % SEGMENTS : (at - prize + SEGMENTS) % SEGMENTS; moved += 1 * SEGMENTS + ahead; // round only once, from the running total, so the error never adds up long target = round(moved * STEPS / SEGMENTS); wheel.moveTo(DIR * target); wheel.runToPosition(); // blocks until the wheel has stopped at = prize; Serial.print("Landed on: "); Serial.println(PRIZES[at]); } }

Stopped · Your code isn't running yet. Until you press Run, the board runs the program already on it.

Nothing printed yet. Press Run.

A 28BYJ-48 stepper moves in exact steps, so the sketch knows where the wheel stops. Press the button and it spins, slows down and lands on a random prize.

Why a stepper always knows where it is
Tune speed and acceleration for a smooth stop
Press and see where it lands

Pin	Connects to	What it does
`D8-D11`	The ULN2003 driver's IN1-IN4	Switch the four coils in turn.
`5V`	The driver board's + and the button	Powers the motor's coils.
`D2`	The button, with a 10 kΩ pull-down	HIGH starts a spin.

Wire it in

Sensors and actuators this board drives, with the real connections.

Push buttonSupply 5 V
Between D2 and GND with pinMode(2, INPUT_PULLUP): reads LOW while pressed. With an external pull-down to GND and the button to 5 V it reads HIGH while pressed instead.
Part pin Board pin
1 D2Wire colour blue
3 GNDWire colour black

Part pin	Board pin
1	D2Wire colour blue
3	GNDWire colour black

All 16 parts on the Arduino Uno R3 page

Spin a prize wheel

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Spin a prize wheel

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in