How to Make a Micro Servo Work with a Micro:bit: A Step-by-Step Guide for Beginners

2.1 Components You Will Need

1x micro:bit board

1x micro servo (e.g., SG90 or similar 9g servo)

1x external power source (3x AA battery pack providing ~4.5V, or 4x AA providing ~6V, is ideal)

Jumper wires (female-to-female or male-to-female as needed)

A micro:bit breakout board or edge connector (optional, but highly recommended for reliable connections)

2.2 Wiring Diagram (Common Ground Connection)

This is the most stable configuration. All grounds must be connected together to form a common reference point.

1. Servo Ground (Brown/Black)→ Connect tomicro:bit GND pinANDExternal Power Supply GND (- terminal) .

2. Servo Power (Red)→ Connect toExternal Power Supply VCC (+ terminal) .

3. Servo Signal (Orange/Yellow)→ Connect tomicro:bit Pin 0(or any other available pin like 1, 2,8, 12, 13, 14, 15, 16).

Example with a 3xAA Battery Pack:

Connect the black wire from the battery pack to the micro:bit’s GND pin and the servo’s brown wire.

Connect the red wire from the battery pack to the servo’s red wire.

Connect the servo’s yellow wire to micro:bit Pin 0.

This ensures that the servo receives its operating power from the batteries while the signal reference is shared with the micro:bit.

3.1 Using Microsoft MakeCode (Blocks)

This is the simplest method for beginners.

1. Go to the MakeCode editor for micro:bit.

2. Add theServo extension:

Click on “Extensions” in the toolbox.

Search for “servo” and add theservolibrary.

3. Use the following block code:

on start servo write pin P0 to 0° pause 1000 ms servo write pin P0 to 90° pause 1000 ms servo write pin P0 to 180°

To run the servo continuously in a loop, use theforeverblock. Theservo write pinblock automatically sets up the PWM signal at 50Hz and adjusts the pulse width for the angle.

3.2 Using MicroPython

For more control, MicroPython provides direct PWM access. This code is verified and includes a function to map angles to duty cycles for the micro:bit’s 20ms PWM period.

from microbit importimport music # Define the PWM period for a servo (20ms)# On micro:bit, the PWM period is set in microseconds. 20ms = 20000us# The duty cycle is a value from 0 to 1023 (10-bit resolution). # Pulse width: 0.5ms (0 deg) to 2.5ms (180 deg) def set_servo_angle(pin, angle): # Constrain the angle to 0-180 if angle 180: angle = 180 # Map angle to pulse width in microseconds: 0.5ms to 2.5ms pulse_width = 500 + (angle2000 / 180) # Convert pulse width to duty cycle for 20ms period duty = int(pulse_width * 1023 / 20000) pin.set_analog_period(20) # 20ms period = 50Hz pin.write_analog(duty) # Main execution while True: # Sweep from 0 to 180 degrees on pin 0 for angle in range(0, 181, 5): set_servo_angle(pin0, angle) sleep(50) # Sweep back from 180 to 0 for angle in range(180, -1, -5): set_servo_angle(pin0, angle) sleep(50)

This code initializes the servo on Pin 0 and sweeps it back and forth continuously.

4.1 Servo Jitters or Twitches Erratically

Symptom:The servo moves back and forth rapidly or makes buzzing sounds without a command.

Cause:The most common cause is an unstable or insufficient power supply. When the servo tries to move, it draws a surge of current. If the voltage drops below a critical level, the micro:bit may reset, or the servo’s logic circuit may malfunction.

Solution:

Use a fresh battery pack:Ensure the external batteries are new or fully charged.

Check ground connection:Verify that the external power supply ground and the micro:bit ground are securely connected.

Add a capacitor:Placing a large electrolytic capacitor (100µF to 1000µF) across the power and ground lines of the servo (red and brown wires) can smooth out voltage spikes. This is a standard practice in robotics.

4.2 Servo Does Not Move at All

Symptom:The servo is silent and does not respond to code.

Cause:This is typically a wiring or signal issue. The servo may not be receiving power, or the signal pin may not be correctly assigned.

Solution:

1. Test the servo:Connect the servo directly to the battery pack (red to +, brown to -) without the micro:bit. The servo should make a slight humming sound or attempt to center. If it does nothing, the servo or battery pack may be faulty.

2. Verify the signal pin:Confirm that the yellow/orange wire is connected to the pin specified in your code (e.g., Pin 0).

3. Check the code:Ensure the servo initialization code (likepin.set_analog_period(20)in MicroPython or theservo writeblock in MakeCode) is being executed.

4.3 Servo Only Moves to Two Positions

Symptom:The servo only moves to 0° and 180°, ignoring intermediate angles.

Cause:The PWM signal is not being generated correctly. This is often due to using a simple digitalwritefunction instead of a proper PWM output or using an incorrect period.

Solution:

In MakeCode:Do not use the standarddigital writepin block. Always use theservo writeblock after adding the extension.

In MicroPython:Do not usepin.write_digital(). Usepin.set_analog_period()followed bypin.write_analog()with a calculated duty cycle as shown in the example above. A 50Hz signal (20ms period) is mandatory for standard servos.