🛠 Asservir un servo moteur avec un potentiomètre (PWM)

Objectives

Control a standard servo motor (pulse-width signal) from the Leonardo using the Servo library, driven by a potentiometer. You will identify the 7 PWM pins on the board (3, 5, 6, 9, 10, 11, 13, using 8-bit PWM via analogWrite) — the Servo library generates pulses using hardware timers on its side — and most importantly, the power supply rules for a servo.

Hardware

• 1 Arduino Leonardo + micro-USB cable
• 1 micro servo (SG90/MG90S type)
• 1 potentiometer on A0 (5V/GND)
• External 5-6 V power supply for the servo if using multiple servos or under load; never from the 3V3 pin (50 mA maximum)

Complete code

#include <Servo.h>

Servo monServo;
const uint8_t POT_PIN   = A0;
const uint8_t SERVO_PIN = 9; // broche PWM (3, 5, 6, 9, 10, 11 ou 13)

void setup {
  monServo.attach(SERVO_PIN); // impulse ~50 Hz, 1 a 2 ms
}

void loop {
  int brut = analogRead(POT_PIN);            // 0..1023
  int angle = map(brut, 0, 1023, 0, 180);    // 0..180 degres
  monServo.write(angle);
  delay(15);
}

Expected verification

The servo arm follows the potentiometer between its two mechanical stops (~0° and ~180°). The motor buzzes slightly when stationary: this is normal for a standard servo. Power the servo from the board's 5V pin for a single small SG90; as soon as it heats up or the board restarts due to insufficient current, switch to an external power supply with a common GND.

Common errors

• Powering the servo from 3V3: this pin is limited to 50 mA, while a servo under peak load requires much more; the board resets.
• No common ground: without GND connected between the external power supply and the Leonardo, the servo vibrates or does not respond.
• Current per pin: official values differ (40 mA on the store page versus 10 mA in tech-specs.yml; check the ATmega32u4 datasheet before designing) — never power a servo directly from a digital pin.
• Forgetting that the Servo library uses timers: on the ATmega32u4, certain PWM channels (analogWrite on 3/5/6/9/10/11/13) and other libraries may cause timer conflicts.
• Non-PWM pin for analogWrite: LEDs blink on/off instead of varying in brightness; only pins 3/5/6/9/10/11/13 are PWM.