Driving a DC Motor with an L293D

Overview

A DC motor can draw hundreds of milliamps and generates voltage spikes when switched, so it must never connect to an Arduino pin. The L293D is an H-bridge chip: two direction inputs choose which way current flows through the motor, and a PWM signal on the enable pin sets the speed. The "D" version has built-in protection diodes.

You will need

• Arduino Uno R3
• L293D (DIP-16)
• Small 3–6 V DC motor
• Separate motor supply (e.g. 4×AA pack)
• 0.1 µF capacitor across the motor terminals (optional)
• Breadboard

Wiring

The sketch

const int ENABLE_PIN = 5;   // PWM: speed
const int IN1_PIN = 7;      // direction
const int IN2_PIN = 8;      // direction

void setMotor(int speed) {  // -255..255; negative = reverse
  if (speed > 0) {
    digitalWrite(IN1_PIN, HIGH);
    digitalWrite(IN2_PIN, LOW);
  } else if (speed < 0) {
    digitalWrite(IN1_PIN, LOW);
    digitalWrite(IN2_PIN, HIGH);
  } else {
    digitalWrite(IN1_PIN, LOW);
    digitalWrite(IN2_PIN, LOW);
  }
  analogWrite(ENABLE_PIN, constrain(abs(speed), 0, 255));
}

void setup() {
  pinMode(ENABLE_PIN, OUTPUT);
  pinMode(IN1_PIN, OUTPUT);
  pinMode(IN2_PIN, OUTPUT);
  setMotor(0);
}

void loop() {
  for (int speed = 0; speed <= 255; speed += 5) {   // speed up forwards
    setMotor(speed);
    delay(40);
  }
  setMotor(0);
  delay(1000);
  for (int speed = 0; speed >= -255; speed -= 5) {  // speed up in reverse
    setMotor(speed);
    delay(40);
  }
  setMotor(0);
  delay(1000);
}

How the code works

Both inputs LOW lets the motor coast; both HIGH brakes it. The L293D is rated 600 mA per channel and drops roughly 1.5–3 V internally, so a 6 V supply may give the motor only about 4 V. For bigger motors use a MOSFET-based driver such as the TB6612FNG or DRV8833. Low PWM values may not overcome the motor's friction, so it starts turning only partway up the ramp.

What you should observe

• The motor speeds up in one direction, stops, speeds up in the other, stops.
• Motor never turns but the chip gets warm: check VCC2 has power and that all grounds are joined.

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