Slowly spin a bipolar stepper motor, with gentle power up and down for smooth steps

.editorconfig

root = true

[*]
charset = utf-8
end_of_line = lf
indent_size = 4
insert_final_newline = true

[{Makefile,*.sh}]
indent_style = tab

[*.ino]
indent_style = space

compile.sh

#!/bin/sh

set -eu

arduino-cli \
	compile \
	--fqbn "$ARDUINO_BOARD" \
	"$STEPPER_PATH"

Makefile

.PHONY: compile \
		setup \
		upload

export ARDUINO_BOARD = arduino:avr:uno
export ARDUINO_CORE = arduino:avr
export ARDUINO_PORT = $(shell find /dev/cu.usbmodem* | head -n 1)
export STEPPER_PATH = $(dir $(abspath $(lastword $(MAKEFILE_LIST))))

.SILENT:

compile:
	./compile.sh

setup:
	./setup.sh

upload:
	./upload.sh

setup.sh

#!/bin/sh

set -eu

if ! command -v arduino-clia 1> /dev/null 2>&1; then
	echo 'setup: missing arduino-cli tool, get it at arduino.github.io/arduino-cli' 1>&2
	exit 1
fi

arduino-cli core install "$ARDUINO_CORE"
arduino-cli lib install Stepper

stepper.ino

#include <Arduino.h>
#include <Stepper.h>

// https://store.arduino.cc/products/arduino-motor-shield-rev3
#define directionA 12
#define directionB 13
#define pwmA 3
#define pwmB 11
#define brakeA 9
#define brakeB 8

// https://www.arduino.cc/reference/en/libraries/stepper/
#define number_of_steps 200
#define rotations_per_minute 200

Stepper stepper = Stepper(number_of_steps, directionA, directionB);

void setup() {
    pinMode(pwmA, OUTPUT);
    pinMode(pwmB, OUTPUT);
    pinMode(brakeA, OUTPUT);
    pinMode(brakeB, OUTPUT);

    analogWrite(pwmA, 0);
    analogWrite(pwmB, 0);
    digitalWrite(brakeA, LOW);
    digitalWrite(brakeB, LOW);

    stepper.setSpeed(rotations_per_minute);
}

void loop() {
    unsigned long timestamp = millis();
    int duty_cycle;

    for (duty_cycle = 0; duty_cycle <= 255; duty_cycle += 3) {
        analogWrite(pwmA, duty_cycle);
        analogWrite(pwmB, duty_cycle);
        delay(2);
    }

    for (duty_cycle = 255; duty_cycle >= 0; duty_cycle -= 3) {
        analogWrite(pwmA, duty_cycle);
        analogWrite(pwmB, duty_cycle);
        delay(1);
    }

    stepper.step(1);
    delay(5000 - (millis() - timestamp));
}

upload.sh

#!/bin/sh

set -eu

main() {
	arduino-cli \
		upload \
		--fqbn "$ARDUINO_BOARD" \
		--port "$ARDUINO_PORT" \
		"$STEPPER_PATH"
}

main