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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

Let’s write a MicroPython program to control the motor.

Note

Open the 3.5_small_fan.py from newton-lab-kit/micropython or copy the code into Thonny, then click “Run” or press F5.
Ensure the correct interpreter is selected: MicroPython (Raspberry Pi Pico).COMxx.

import machine
import utime

# Define the control pins
motor_in1 = machine.Pin(14, machine.Pin.OUT)
motor_in2 = machine.Pin(15, machine.Pin.OUT)

def rotate_clockwise():
    motor_in1.high()
    motor_in2.low()

def rotate_counterclockwise():
    motor_in1.low()
    motor_in2.high()

def stop_motor():
    motor_in1.low()
    motor_in2.low()

while True:
    rotate_clockwise()
    utime.sleep(1)
    stop_motor()
    utime.sleep(1)
    rotate_counterclockwise()
    utime.sleep(1)
    stop_motor()
    utime.sleep(1)

When the code is running, the motor will rotate clockwise for one second, stop for one second, rotate counterclockwise for one second, and then stop for one second, in a loop.

Understanding the Code

Initialize the Pins:

motor_in1 and motor_in2 are connected to GP14 and GP15, controlling the direction of the motor.
```
motor_in1 = machine.Pin(14, machine.Pin.OUT)
motor_in2 = machine.Pin(15, machine.Pin.OUT)
```
Define Functions:
- rotate_clockwise(): Sets motor_in1 high and motor_in2 low to rotate the motor clockwise.
- rotate_counterclockwise(): Sets motor_in1 low and motor_in2 high to rotate counterclockwise.
- stop_motor(): Sets both motor_in1 and motor_in2 low to stop the motor.

Main Loop:

The motor rotates clockwise, stops, rotates counterclockwise, and stops again, each for one second, repeatedly.

while True:
    rotate_clockwise()
    utime.sleep(1)
    stop_motor()
    utime.sleep(1)
    rotate_counterclockwise()
    utime.sleep(1)
    stop_motor()
    utime.sleep(1)

Troubleshooting Tips

Motor Keeps Spinning After Stopping the Script:

If the motor continues to run after stopping the program, you may need to reset the Pico. Use a wire or a button to momentarily connect the RUN pin to GND, which resets the Pico.
Pico Disconnects or Becomes Unresponsive:

The motor may draw too much current, causing voltage fluctuations. Ensure you’re using a separate power supply for the motor and that all grounds are connected.

Conclusion

In this lesson, you’ve learned how to control a DC motor using the L293D motor driver and the Raspberry Pi Pico 2. You can now control the motor’s direction and create projects like a small fan or a motorized device.

Next Steps

Speed Control: Try using PWM (Pulse Width Modulation) to control the speed of the motor by connecting the EN1 pin to a PWM-capable GPIO pin.
Control Multiple Motors: Use the other channels of the L293D to control additional motors.
Sensor Integration: Incorporate sensors to control the motor based on input (e.g., temperature, light).