Motor speed control

/*
  10 — Motor speed control
  Board: ESP32.  Parts: potentiometer, DC motor, L9110 module.

  Wiring:
    Potentiometer: outer legs -> 3V3 and GND, wiper -> GPIO 35
    L9110 module:  VCC -> VIN (5 V), GND -> GND, A-1A -> GPIO 16, A-1B -> GPIO 17
                   Motor -> the module's MOTOR A screw terminals
                   (never a motor straight on a GPIO: far too much current, and
                    a voltage spike back down the line when it stops)

  Turn the knob, the motor changes speed. PWM switches the power on and off
  faster than the motor can respond, so the average voltage — and the speed —
  follows the duty cycle. Below ~30 % most small motors just hum: MIN_DUTY skips that.
*/

const int POT_PIN = 35;
const int A1A_PIN = 16;     // PWM = speed
const int A1B_PIN = 17;     // LOW  = forward (swap the two for reverse)
const int MIN_DUTY = 70;    // 0..255; below this the motor stalls and hums

void setup() {
  Serial.begin(115200);
  pinMode(A1A_PIN, OUTPUT);
  pinMode(A1B_PIN, OUTPUT);
  digitalWrite(A1B_PIN, LOW);
}

void loop() {
  int raw  = analogRead(POT_PIN);                 // 0..4095
  int duty = map(raw, 0, 4095, 0, 255);
  if (duty < 8) duty = 0;                         // knob at the bottom = fully off
  else if (duty < MIN_DUTY) duty = MIN_DUTY;

  analogWrite(A1A_PIN, duty);                     // ESP32 core 2.0.2+ supports analogWrite

  Serial.print("knob "); Serial.print(raw); Serial.print("  duty "); Serial.println(duty);
  delay(50);
}