const int TX_PIN = 12;
const int RX_PIN = 13;
const int SAMPLES = 100;

long baseline = 0;

long readCapacitance() {
  long total = 0;
  for (int i = 0; i < SAMPLES; i++) {
    pinMode(RX_PIN, OUTPUT);
    digitalWrite(RX_PIN, LOW);
    digitalWrite(TX_PIN, LOW);
    delayMicroseconds(20);

    pinMode(RX_PIN, INPUT);
    digitalWrite(TX_PIN, HIGH);
    delayMicroseconds(50);  // longer charge window

    total += analogRead(RX_PIN);

    digitalWrite(TX_PIN, LOW);
    delayMicroseconds(20);
  }
  return total / SAMPLES;
}

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

  // calibrate baseline over 200 readings at startup
  // don't touch the pads during this
  long sum = 0;
  for (int i = 0; i < 200; i++) {
    sum += readCapacitance();
    delay(10);
  }
  baseline = sum / 200;
  Serial.print("Baseline: ");
  Serial.println(baseline);
}

void loop() {
  long val = readCapacitance();
  long delta = baseline - val;  // positive delta = more capacitance = hand present

  Serial.println(delta);  // plot this — should be ~0 at rest, positive on approach

  if (delta > 300) {
    Serial.println("TOUCH");
  } else if (delta > 80) {
    Serial.println("PROXIMITY");
  }

  delay(20);
}