Motors & Relays — Arduino Nano

Control DC motors and relays from an Arduino Nano. This guide covers H-bridge (L298/L293) motor drivers, simple MOSFET motor switching, and driving mechanical relays safely.

Estimated time: ~30–45 minutes.

Parts & tools

• Arduino Nano
• DC motor(s) (3–12V typical)
• Motor driver (L298N or L293) or N-channel logic-level MOSFET (e.g., IRLZ44N)
• Diode-protected mechanical relay or relay module (with transistor driver)
• Flyback diodes (1N400x) for motors/inductive loads
• External motor power supply (matched to motor voltage)
• Heat sink for driver (if required), breadboard and jumper wires

Wiring

• H-bridge (L298N): connect motor power to VMS, logic supply to 5V, and common GND to the Nano. EN -> PWM pin (e.g., D3), IN1/IN2 -> direction pins (e.g., D4, D5).
• MOSFET low-side switch: Gate -> PWM pin through 100Ω, Drain -> motor negative, Source -> GND; motor positive -> external supply. Place a diode across the motor terminals (cathode to +V).
• Relay (via transistor): Nano GPIO -> base resistor (1kΩ) -> NPN base; emitter -> GND; collector -> relay coil negative; relay coil positive -> Vrelay. Add diode across coil.

Safety: never power motors from the Nano's 5V pin. Use a separate motor supply and always connect grounds together. Add decoupling capacitors and flyback diodes to prevent spikes.

Example: Motor control with L298N

const int enA = 3; // PWM pin
const int in1 = 4;
const int in2 = 5;

void setup() {
  pinMode(enA, OUTPUT);
  pinMode(in1, OUTPUT);
  pinMode(in2, OUTPUT);
}

void driveForward(int speed) {
  digitalWrite(in1, HIGH);
  digitalWrite(in2, LOW);
  analogWrite(enA, speed);
}

void driveReverse(int speed) {
  digitalWrite(in1, LOW);
  digitalWrite(in2, HIGH);
  analogWrite(enA, speed);
}

void loop() {
  driveForward(200);
  delay(2000);
  driveReverse(200);
  delay(2000);
  analogWrite(enA, 0);
  delay(1000);
}

Example: Relay switching (via transistor)

const int relayPin = 7; // drives transistor base via resistor

void setup() {
  pinMode(relayPin, OUTPUT);
}

void loop() {
  digitalWrite(relayPin, HIGH); // energise relay
  delay(1000);
  digitalWrite(relayPin, LOW); // de-energise
  delay(1000);
}

Tests

1. Verify motor supply voltage with a multimeter before connecting the motor.
2. Test direction pins and PWM with no-load and low duty-cycle.
3. Test relay switching with an LED or low-voltage load before connecting high-voltage mains.

Troubleshooting

• Nano resets when motor starts: power draw too high — use a dedicated motor supply and decoupling.
• Motor driver overheating: check current rating, add heatsink or use a MOSFET-based driver.
• Relay chattering: ensure stable supply and add snubber for inductive loads.

Migration notes (ESP32 / other boards)

• ESP32 uses 3.3V logic and a different PWM API (ledcAttachPin/ledcWrite). Ensure driver inputs accept 3.3V or use level shifters.
• Pin mapping and PWM frequency differ — map pins carefully and test PWM behaviour.

Next steps

• Add encoder feedback for closed-loop speed/position control.
• Add current sensing (ACS712 or shunt + amplifier) for stall detection and safety.