28BYJ-48 Stepper motor controlled by Microbit with a Microshield

While operating the miniature stepper motor 28BYJ-48 without a ULN2003—a dedicated motor driver chip that protects circuitry from high currents—risks damaging both the Microshield and the micro:bit, the immediate outcomes offer fascinating insights for electronics enthusiasts.

In this setup, the micro:bit logo serves as a capacitive touch button to manage the motor's state machine. An initial press triggers clockwise rotation, while a subsequent press reverses the direction to counter-clockwise following a precise 1200ms pause. Furthermore, registering a double-press in under one second acts as an immediate override to stop the motor completely.

Check out the video and accompanying code below.

let motorState = 0 // 0 = Stopped, 1 = CW, 2 = Transitioning/Pausing, 3 = CCW
let lastPressTime = 0
let currentPressTime = 0

input.onLogoEvent(TouchButtonEvent.Pressed, function () {
    currentPressTime = input.runningTime()

    // 1. Double-click detection (less than 1000ms apart) -> Always STOP
    if (motorState != 0 && (currentPressTime - lastPressTime < 1000)) {
        motorState = 0
    } else {
        // 2. Single-click state machine transitions
        if (motorState == 0) {
            motorState = 1 // From Stopped -> Go CW
        } else if (motorState == 1) {
            motorState = 2 // From CW -> Trigger Pause then CCW
        } else if (motorState == 3) {
            motorState = 1 // From CCW -> Instant reverse back to CW
        }
    }
    lastPressTime = currentPressTime
})

basic.forever(function () {
    if (motorState == 1) {
        // Rotate Clockwise (CW)
        microshield.Stepper(microshield.Steppers.STEP1, 30, microshield.stepUnit.Degrees)
        basic.pause(10) // Small stability delay

    } else if (motorState == 2) {
        // The 1200ms pause sequence before CCW begins
        basic.pause(1200)
        // Safety check: If the user double-clicked to STOP during those 1.2 seconds, 
        // don't start the CCW motor. Otherwise, switch to CCW state.
        if (motorState == 2) {
            motorState = 3
        }

    } else if (motorState == 3) {
        // Rotate Counter-Clockwise (CCW)
        microshield.Stepper(microshield.Steppers.STEP1, -30, microshield.stepUnit.Degrees)
        basic.pause(10) // Small stability delay

    } else {
        // motorState == 0 (Stopped)
        basic.pause(100) // Idle low-power pause
    }
})