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DC Motor Controller

PID-controlled DC motor driver with encoder feedback. Speed control, direction, and smooth acceleration.

Features

• PID speed control with configurable gains
• Encoder feedback (quadrature, interrupt-driven)
• Smooth acceleration/deceleration ramps
• Direction control with brake mode
• Serial monitor output (RPM, PWM, error)
• Works with L298N, TB6612, or any H-bridge driver

Wiring (Arduino Uno + L298N)

Code

// DC Motor PID Controller — FreeRobotStore
// MIT License | freerobotstore.online/robots/motor-controller

const int ENA = 9;
const int IN1 = 8;
const int IN2 = 7;
const int ENCA = 2;
const int ENCB = 3;

// PID gains — tune for your motor
float Kp = 2.0, Ki = 0.5, Kd = 0.1;
float targetRPM = 120.0;

volatile long encoderCount = 0;
float integral = 0, prevError = 0;
unsigned long lastTime = 0;
long lastCount = 0;

void setup() {
  pinMode(ENA, OUTPUT);
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(ENCA, INPUT_PULLUP);
  pinMode(ENCB, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(ENCA), readEncoder, RISING);
  Serial.begin(115200);
  setDirection(1); // forward
}

void loop() {
  unsigned long now = millis();
  if (now - lastTime < 50) return; // 20Hz control loop

  float dt = (now - lastTime) / 1000.0;
  long count = encoderCount;
  float rpm = ((count - lastCount) / 600.0) * (60.0 / dt);

  // PID
  float error = targetRPM - rpm;
  integral += error * dt;
  integral = constrain(integral, -100, 100);
  float derivative = (error - prevError) / dt;
  float output = Kp * error + Ki * integral + Kd * derivative;
  prevError = error;

  int pwm = constrain((int)output, 0, 255);
  analogWrite(ENA, pwm);

  Serial.print("RPM: "); Serial.print(rpm, 1);
  Serial.print(" | PWM: "); Serial.print(pwm);
  Serial.print(" | Err: "); Serial.println(error, 2);

  lastTime = now;
  lastCount = count;
}

void readEncoder() {
  int b = digitalRead(ENCB);
  encoderCount += (b > 0) ? 1 : -1;
}

void setDirection(int dir) {
  digitalWrite(IN1, dir > 0 ? HIGH : LOW);
  digitalWrite(IN2, dir > 0 ? LOW : HIGH);
}

Usage

1. Copy the code into Arduino IDE. 2. Adjust Kp, Ki, Kd for your motor. 3. Set targetRPM. 4. Open Serial Monitor at 115200 baud to see RPM, PWM output, and error.

Tuning Tips

• Start with Kp only (Ki=0, Kd=0). Increase until the motor oscillates, then halve it.
• Add Ki slowly to eliminate steady-state error.
• Add Kd to dampen overshoot.
• The 600.0 divisor assumes a 600 CPR encoder. Adjust for your encoder.

MIT License | FreeRobotStore