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3.5 Controlling a Small Fan (DC Motor)

In this lesson, we’ll learn how to control a DC motor (like a small fan) using the Raspberry Pi Pico 2 and an L293D motor driver. The L293D allows us to control the direction of the motor rotation—both clockwise and counterclockwise. Since DC motors require more current than the Pico can provide directly, we’ll use an external power supply to safely power the motor.

What You’ll Need

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Newton Lab Kit	450+	Newton Lab Kit

You can also buy them separately from the links below.

SN	COMPONENT	QUANTITY	LINK
1	Raspberry Pi Pico 2	1	BUY
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	IC L293D	1
6	DC Motor	1	BUY
7	Power Supply Module	1
8	9V Battery	1

Circuit Diagram

sch_motor

L293D is a motor driver chip, EN is connected to 5V to make L293D work. 1A and 2A are the inputs connected to GP15 and GP14 respectively; 1Y and 2Y are the outputs connected to the two ends of the motor.

Y (output) is in phase with A (input), so if GP15 and GP14 are given different levels respectively, the direction of motor rotation can be changed.

Wiring Diagram

In this circuit, you will see that the button is connected to the RUN pin. This is because the motor is operating with too much current, which may cause the Pico to disconnect from the computer, and the button needs to be pressed (for the Pico’s RUN pin to receive a low level) to reset.

Since DC motors require a high current, we use a power supply module to power the motor here for safety reasons.

Writing the Code

Note

You can open the file 3.5_small_fan.ino from newton-lab-kit/arduino/3.5_small_fan.
Or copy this code into Arduino IDE.
Select the Raspberry Pi Pico 2 board and the correct port, then click “Upload”.

const int IN1 = 15; // GPIO pin connected to Input 1A
const int IN2 = 14; // GPIO pin connected to Input 2A

void setup() {
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
}

void loop() {
  // Rotate motor clockwise
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  delay(2000); // Run for 2 seconds

  // Stop motor
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
  delay(1000); // Stop for 1 second

  // Rotate motor counterclockwise
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, HIGH);
  delay(2000); // Run for 2 seconds

  // Stop motor
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
  delay(1000); // Stop for 1 second
}

After uploading the code:

The motor should rotate in one direction for 2 seconds.
Then, it will stop for 1 second.
Then, it will rotate in the opposite direction for 2 seconds.
This cycle repeats indefinitely.

Understanding the Code

Defining Control Pins:

const int IN1 = 15; // Connected to Input 1A
const int IN2 = 14; // Connected to Input 2A

Setting Pin Modes:

void setup() {
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
}

Controlling Motor Direction:
- Clockwise Rotation: Sets IN1 HIGH and IN2 LOW, causing the motor to rotate in one direction.
```
digitalWrite(IN1, HIGH);
digitalWrite(IN2, LOW);
```
- Counterclockwise Rotation: Sets IN1 LOW and IN2 HIGH, causing the motor to rotate in the opposite direction.
```
digitalWrite(IN1, LOW);
digitalWrite(IN2, HIGH);
```
Stopping the Motor:

Sets both inputs LOW, stopping the motor.
```
digitalWrite(IN1, LOW);
digitalWrite(IN2, LOW);
```

Further Exploration

Speed Control:

Use Pulse Width Modulation (PWM) to control the speed of the motor by connecting the EN1 pin to a PWM-capable GPIO pin and varying the duty cycle.
Controlling Multiple Motors:

The L293D can control two motors. Try adding a second motor and controlling it independently.
Sensor Integration:

Incorporate sensors (e.g., limit switches, encoders) to create more advanced motor control systems.

Safety Precautions

Power Supply:
- Ensure that the external power supply voltage matches the motor’s voltage rating.
- Do not power the motor directly from the Pico’s 3.3V pin.
Current Draw:
- Motors can draw significant current, especially during startup or when stalled.
- Ensure that your power supply can handle the motor’s current requirements.
Resetting the Pico:
- In some cases, the motor’s current draw may cause voltage dips, leading the Pico to reset or disconnect.
- If you encounter issues uploading code after running the motor, you can manually reset the Pico by connecting the RUN pin to GND momentarily.

Conclusion

In this lesson, you’ve learned how to control a DC motor using the Raspberry Pi Pico and the L293D motor driver. By controlling the inputs to the L293D, you can change the direction of the motor’s rotation. This fundamental concept is essential in robotics, automation, and many other applications involving motors.