const int TX_PIN = 12;
const int RX_PIN = 13;
const int SAMPLES = 50;

const int PROX_THRESHOLD = 1800;   // tune these after watching serial plotter
const int TOUCH_THRESHOLD = 3000;

long readCapacitance() {
  long total = 0;
  for (int i = 0; i < SAMPLES; i++) {
    // discharge RX fully
    pinMode(RX_PIN, OUTPUT);
    digitalWrite(RX_PIN, LOW);
    digitalWrite(TX_PIN, LOW);
    delayMicroseconds(10);

    // float RX, then pulse TX high
    pinMode(RX_PIN, INPUT);
    digitalWrite(TX_PIN, HIGH);
    delayMicroseconds(5);  // fixed charge window — tune this (1–20µs)

    // read the voltage that coupled onto RX
    total += analogRead(RX_PIN);

    // reset TX
    digitalWrite(TX_PIN, LOW);
    delayMicroseconds(5);
  }
  return total / SAMPLES;
}

void setup() {
  Serial.begin(115200);
  pinMode(TX_PIN, OUTPUT);
  digitalWrite(TX_PIN, LOW);
}

void loop() {
  long val = readCapacitance();
  Serial.println(val);  // open Serial Plotter to watch this live

  if (val > TOUCH_THRESHOLD) {
    Serial.println("TOUCH");
  } else if (val > PROX_THRESHOLD) {
    Serial.println("PROXIMITY");
  }

  delay(20);
}