🛠 Détecter un contact avec les broches tactiles capacitives

Objectives

Leverage the specific advantage of the ESP32-S2: 14 hardware capacitive touch pins (GPIO1 to GPIO14). Learn to read capacitance with touchRead, calibrate a threshold, and trigger an action upon finger contact.

Hardware

• ESP32-S2 board
• Adhesive copper tape (or metal plate, or simply a 5 cm wire)
• 1 LED + 330 Ω resistor
• Dupont cables

Complete code

// Tactile capacitif sur ESP32-S2 (GPIO1 a GPIO14 seulement)
const uint8_t TACT_PIN = 4;    // broche tactile capacitive
const uint8_t LED_PIN  = 2;
uint16_t seuil = 0;            // calibre au demarrage

void setup {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  delay(500);
  uint32_t somme = 0;
  for (int i = 0; i < 50; i++) { somme += touchRead(TACT_PIN); delay(5); }
  seuil = somme / 50 + 2000;   // valeur au repos + marge
  Serial.printf("Seuil calibre : %u\n", seuil);
}

void loop {
  uint16_t valeur = touchRead(TACT_PIN);
  bool touche = valeur > seuil;
  digitalWrite(LED_PIN, touche ? HIGH : LOW);
  static uint16_t derniere = 0;
  if (abs((int)valeur - (int)derniere) > 100) {  // limite le spam
    Serial.printf("touch=%u  touche=%s\n", valeur, touche ? "OUI" : "non");
    derniere = valeur;
  }
  delay(50);
}

Expected verification

At startup, the program calibrates the threshold based on the resting value. The serial monitor displays the measured capacitance; as soon as a finger touches the copper plate, the value exceeds the threshold, the LED turns on, and "touch=YES" is displayed. Without contact, the LED remains off.

Common errors

• Choosing a pin outside GPIO1-14: only this range is touch-capable on the S2; a touchRead on GPIO2 returns an inconsistent value.
• Hardcoding the threshold in the code without calibration: humidity and wiring shift the resting value, so always calibrate at startup.
• Calibrating with a finger on the sensor: the threshold becomes skewed and no contact is detected anymore; remove your hand during setup.
• Touch wire too long without insulation: the sensor becomes unstable, keep it under 10 cm.