Radar-style scanner

/*
  12 — Radar-style scanner
  Board: ESP32.  Parts: SG90 servo, HC-SR04, LCD 1602 (I2C backpack), 3 x 1 kΩ.
  Libraries: "ESP32Servo", "LiquidCrystal I2C" (Frank de Brabander).

  Wiring:
    SG90:    brown -> GND, red -> VIN (5 V), signal -> GPIO 13; mount the HC-SR04 on the horn
    HC-SR04: VCC -> VIN, GND -> GND, TRIG -> GPIO 5
             ECHO -> 1 kΩ -> GPIO 18, then two 1 kΩ in series from GPIO 18 -> GND
    LCD:     VCC -> VIN, GND -> GND, SDA -> GPIO 21, SCL -> GPIO 22

  Sweep the sensor through its range and record distance at each angle. The
  output is a set of angle/distance pairs — a crude map of what is in front —
  printed to Serial as CSV (angle,cm) and summarised on the LCD.
*/

#include <ESP32Servo.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const int SERVO_PIN = 13, TRIG_PIN = 5, ECHO_PIN = 18;
const int SWEEP_FROM = 15, SWEEP_TO = 165, STEP_DEG = 5;

Servo servo;
LiquidCrystal_I2C lcd(0x27, 16, 2);

float readCm() {
  digitalWrite(TRIG_PIN, LOW);  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  unsigned long us = pulseIn(ECHO_PIN, HIGH, 25000UL);
  return us == 0 ? -1 : us / 58.0;
}

void scan(int from, int to, int step) {
  float nearest = 1e9; int nearestAt = -1;
  for (int a = from; (step > 0) ? a <= to : a >= to; a += step) {
    servo.write(a);
    delay(60);                                   // let the horn settle
    float cm = readCm();
    Serial.print(a); Serial.print(","); Serial.println(cm, 1);   // CSV: angle,cm
    if (cm > 0 && cm < nearest) { nearest = cm; nearestAt = a; }
    lcd.setCursor(0, 0);
    lcd.print("angle "); lcd.print(a); lcd.print((char)223); lcd.print("     ");
  }
  lcd.setCursor(0, 1);
  if (nearestAt < 0) lcd.print("nothing in range");
  else { lcd.print("near "); lcd.print(nearest, 0); lcd.print("cm @"); lcd.print(nearestAt); lcd.print((char)223); lcd.print("  "); }
}

void setup() {
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  servo.setPeriodHertz(50);
  servo.attach(SERVO_PIN, 500, 2400);
  lcd.init(); lcd.backlight();
  lcd.print("Scanning...");
  Serial.println("angle,cm");
}

void loop() {
  scan(SWEEP_FROM, SWEEP_TO,  STEP_DEG);
  scan(SWEEP_TO,   SWEEP_FROM, -STEP_DEG);
}