Waving Desk Robot: ESP32 servo basics without a library

/*
 * TinyBot Forge — Waving Desk Robot (servo basics)
 * https://tinybotforge.com/en/
 *
 * No servo library: the ESP32 LEDC peripheral generates the 50 Hz servo signal directly.
 * Hardware: ESP32 DevKit V1, SG90 servo, HC-SR04 (optional: wave only when someone is near)
 * Toolchain: Arduino IDE 2.x + ESP32 board package 3.x
 */

const int PIN_SERVO = 23;
const int PIN_TRIG = 18;
const int PIN_ECHO = 19;       // HC-SR04 ECHO needs a 1k/2k voltage divider
const bool USE_SENSOR = true;  // no sensor? set to false and it waves every 5 s

// SG90: 20 ms period (50 Hz); ~0.5 ms pulse = 0°, ~2.4 ms = 180°
const int SERVO_FREQ = 50;
const int SERVO_BITS = 14;           // 14 bit -> 0-16383
const int PULSE_MIN_US = 500;
const int PULSE_MAX_US = 2400;
const float WAVE_TRIGGER_CM = 40.0;

void servoWrite(int angle) {
  angle = constrain(angle, 0, 180);
  int us = map(angle, 0, 180, PULSE_MIN_US, PULSE_MAX_US);
  // pulse width to duty: duty = us / 20000 * 16383
  uint32_t duty = (uint32_t)us * ((1UL << SERVO_BITS) - 1) / 20000UL;
  ledcWrite(PIN_SERVO, duty);
}

// Smooth move one degree at a time: looks natural and avoids current spikes
void servoSweep(int from, int to, int stepDelayMs) {
  int step = (to > from) ? 1 : -1;
  for (int a = from; a != to; a += step) {
    servoWrite(a);
    delay(stepDelayMs);
  }
  servoWrite(to);
}

float readDistanceCm() {
  digitalWrite(PIN_TRIG, LOW);  delayMicroseconds(2);
  digitalWrite(PIN_TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(PIN_TRIG, LOW);
  unsigned long us = pulseIn(PIN_ECHO, HIGH, 25000UL);
  return us == 0 ? 999.0 : us / 58.0;
}

void wave() {
  servoSweep(90, 150, 4);          // raise arm
  for (int i = 0; i < 3; i++) {    // wave three times
    servoSweep(150, 110, 3);
    servoSweep(110, 150, 3);
  }
  servoSweep(150, 90, 6);          // lower arm
}

void setup() {
  Serial.begin(115200);
  pinMode(PIN_TRIG, OUTPUT);
  pinMode(PIN_ECHO, INPUT);
  ledcAttach(PIN_SERVO, SERVO_FREQ, SERVO_BITS);
  servoWrite(90);
  delay(500);
}

void loop() {
  if (USE_SENSOR) {
    float cm = readDistanceCm();
    Serial.printf("distance %.1f cm\n", cm);
    if (cm < WAVE_TRIGGER_CM) {
      wave();
      delay(1500);  // pause so it doesn't wave nonstop
    }
    delay(100);
  } else {
    wave();
    delay(5000);
  }
}