Controlling a Servo with MicroPython

Welcome to the Servo Lab

Monty waving welcome Servos are special motors that can move to a precise angle and hold it there. You will use them to make robot arms, camera pans, and steering systems. Let's build something amazing!

What Is a Servo?

A servo is a motor with a built-in position sensor and control circuit. You tell it an angle — say, 90 degrees — and it rotates to exactly that position and stays there.

A typical hobby servo can move from 0 degrees to 180 degrees.

Parts You Need

Part	Quantity	Approximate Cost
Raspberry Pi Pico	1	$4
SG90 Micro Servo	1	$2–$4
Solderless breadboard	1	$3
Jumper wires	3	—

Servo Connections

Almost every hobby servo has a three-wire connector:

Wire color	Signal	Where to connect
Brown or Black	Ground (GND)	Pico GND pin
Red	Power (5 V)	Pico VBUS pin (pin 40)
Orange or Yellow	Signal (data)	GP15 (or any PWM-capable pin)

Watch Out!

Monty warning Servos run on 5 V power but accept a 3.3 V signal from the Pico. Connect the red wire to VBUS (the 5 V USB pin), not to the 3V3 pin. Using 3.3 V power will make the servo weak or unreliable.

How Servo Control Works

Servos use a signal called Pulse-Width Modulation (PWM). The Pico sends short pulses at 50 times per second (50 Hz). The length of each pulse tells the servo where to move:

A pulse of 1 millisecond (ms) → 0 degrees
A pulse of 1.5 ms → 90 degrees (center)
A pulse of 2 ms → 180 degrees

Key Idea

Monty thinking The Pico's duty_u16() value ranges from 0 to 65 535. At 50 Hz, a 1 ms pulse equals a duty value of about 1 638, and a 2 ms pulse equals about 3 276.

Wiring Steps

Place the servo near your breadboard.
Connect the brown/black wire to any GND pin on the Pico.
Connect the red wire to VBUS (pin 40 on the Pico).
Connect the orange/yellow wire to GP15 on the Pico.

Sample Program

from machine import Pin, PWM
import time

# Create a PWM signal on GP15 for the servo signal wire
servo_pin = PWM(Pin(15))
servo_pin.freq(50)  # servos need a 50 Hz signal

def set_angle(degrees):
    """Move the servo to the given angle (0 to 180 degrees)."""
    # Convert degrees to a pulse width between 1 ms and 2 ms
    # At 50 Hz, one full cycle = 20 ms = 65535 duty units
    # 1 ms pulse = 65535 / 20 = 3276 units
    # 2 ms pulse = 65535 / 10 = 6553 units
    min_duty = 1638   # duty value for 0 degrees  (0.5 ms pulse)
    max_duty = 8192   # duty value for 180 degrees (2.5 ms pulse)
    duty = int(min_duty + (max_duty - min_duty) * degrees / 180)
    servo_pin.duty_u16(duty)

# Sweep from 0 to 180 degrees and back
while True:
    for angle in range(0, 181, 10):   # 0 → 180 in steps of 10
        set_angle(angle)
        time.sleep(0.05)              # wait 50 ms between steps
    for angle in range(180, -1, -10): # 180 → 0 in steps of 10
        set_angle(angle)
        time.sleep(0.05)

What Each Line Does

Line	Purpose
`PWM(Pin(15))`	Creates a PWM signal on GP15
`servo_pin.freq(50)`	Sets the frequency to 50 Hz (required for servos)
`min_duty = 1638`	Duty value that produces a 0.5 ms pulse (0°)
`max_duty = 8192`	Duty value that produces a 2.5 ms pulse (180°)
`servo_pin.duty_u16(duty)`	Sends the calculated pulse width to the servo
`range(0, 181, 10)`	Counts from 0 to 180 in steps of 10

Monty's Tip

Monty giving a tip If your servo buzzes at the ends of its range, the min_duty and max_duty values may be slightly off for your particular servo model. Try adjusting min_duty up by 100 or max_duty down by 100 until the buzzing stops.

Moving to a Specific Angle

Instead of the sweep loop, you can move to one specific position:

set_angle(0)    # move to 0 degrees
time.sleep(1)

set_angle(90)   # move to center
time.sleep(1)

set_angle(180)  # move to 180 degrees
time.sleep(1)

Great Work!

Monty celebrating You can now move a servo to any angle with just a few lines of code. Next, try combining the servo with a button or potentiometer so a human can control the angle in real time!