Servo¶

A servo is a small geared motor that stops at a precise angle — exactly what you need for a robot arm, the steering of a small RC car, or a self-opening lid. Here we drive it from the ESP32 in MicroPython, through PWM at 50 Hz.

Description¶

A hobby servo (SG90, MG90, SG5010) expects a short pulse repeated every 20 ms on the signal wire. The pulse width sets the angle:

• ~0.5 ms → 0°
• ~1.5 ms → 90° (center)
• ~2.4 ms → 180°

There's no built-in Servo library on the ESP32 the way there is on Arduino — we use machine.PWM directly at 50 Hz and compute the duty from the angle. At 10-bit resolution (0–1023), a 1 ms pulse is duty ≈ 51 and a 2 ms pulse is duty ≈ 102.

Components¶

SG90 specs¶

• Operating voltage: 4.8 – 6 V
• Torque: ~1.6 kg·cm at 4.8 V
• Speed: ~0.12 s / 60°

Wiring¶

    ESP32                Servo SG90
   GPIO 13 ──── orange ── Signal
     5V / Vin ── red    ── Power (+)
     GND ────── brown  ── Ground (−)

Code¶

from machine import Pin, PWM
import time

# --- Setup ---

SERVO_PIN = 13
FREQ = 50          # 50 Hz = 20 ms period (what the servo expects)

# Duty for SG90 at 10-bit resolution:
#   0°   → 0.5 ms pulse  → duty ≈ 26
#   90°  → 1.5 ms pulse  → duty ≈ 77
#   180° → 2.4 ms pulse  → duty ≈ 123
DUTY_MIN = 26
DUTY_MAX = 123

servo = PWM(Pin(SERVO_PIN), freq=FREQ, duty=0)


def set_angle(angle):
    """Set the servo angle between 0 and 180 degrees."""
    angle = max(0, min(180, angle))                    # clamp
    duty = DUTY_MIN + (DUTY_MAX - DUTY_MIN) * angle // 180
    servo.duty(duty)


def sweep():
    """Slow sweep 0° → 180° → 0°."""
    for a in range(0, 181, 2):
        set_angle(a)
        time.sleep_ms(15)
    for a in range(180, -1, -2):
        set_angle(a)
        time.sleep_ms(15)


try:
    while True:
        sweep()
except KeyboardInterrupt:
    set_angle(90)        # park at center
    time.sleep_ms(500)
    servo.deinit()

Run the script¶

1. Plug the ESP32 into USB.
2. In Thonny, paste the code and save it as main.py on the MicroPython device.
3. Press Run (F5). The servo shaft should slowly sweep from 0° to 180° and back.

If the servo jerks and then dies, see Troubleshooting.

Calibration¶

Cheap servos vary between units — your SG90's real travel may be 5°…175° rather than 0°…180°. If at angle=0 you hear a buzz (the shaft is jammed against a mechanical stop), bump DUTY_MIN up by 2-3 counts. If angle=180 doesn't reach the end, raise DUTY_MAX.

# Test the ends before using sweep()
set_angle(0)     # should glide cleanly to the left
time.sleep(1)
set_angle(180)   # then to the right

Example: angle from the REPL¶

Send an angle from Thonny's REPL and the servo goes straight there:

from machine import Pin, PWM

servo = PWM(Pin(13), freq=50)
DUTY_MIN, DUTY_MAX = 26, 123

def set_angle(a):
    a = max(0, min(180, a))
    servo.duty(DUTY_MIN + (DUTY_MAX - DUTY_MIN) * a // 180)

# In the REPL: set_angle(45), set_angle(120), etc.

Troubleshooting¶

Extension ideas¶

• Joystick → servo: read a pot on GPIO 34 (ADC1) and map 0–4095 to 0–180°. See Robot Car Remote for a full example of joystick-on-ADC.
• Pan/tilt with two servos: one horizontal, one vertical, mounted on a small bracket — the basis for a camera that tracks an object.
• Robot status indicator: combine with the RGB LED to signal state (green = idle, red = moving).
• Wireless control: send the angle over ESP-NOW from a remote — no cables, no Wi-Fi.

References¶

• MicroPython — machine.PWM reference
• Random Nerd Tutorials — ESP32 with Servo Motor