Read what the charger offers

// Read what a USB-C source is advertising, from the breakout's CC pads.
//
// Wiring:
//   breakout GND  -> ESP32 GND
//   breakout CC1  -> ESP32 GPIO34
//   breakout CC2  -> ESP32 GPIO35
//   breakout VBUS -> leave it unconnected for this sketch
//
// Power the ESP32 from its own USB cable. Do not also feed VBUS into the
// board's 5V pin while it is plugged into your computer — that joins two
// supplies together. The point here is to listen to CC, and CC needs only
// the ground wire and the two signal wires.
//
// CC never goes above about 1.7 V on a 5 V source with the 5.1k pull-downs
// fitted, so it is safe on an ESP32 input directly. If you ever read more
// than 2 V here, unplug and find out why before trusting the number.
//
// Arduino IDE: Tools > Board > esp32 > ESP32 Dev Module, then Tools > Port
// and pick the port the board appears on. No libraries.

const int CC1_PIN = 34;
const int CC2_PIN = 35;

// Roughly where a sink decides one advertised band has become the next.
// From the USB Type-C specification, not from this board.
const float EDGE_1V5 = 0.66;   // volts
const float EDGE_3A  = 1.23;

// Anything below this is an open CC line: the one the cable left alone.
const float OPEN_MAX = 0.20;

float readVolts(int pin) {
  // Average a few samples - the ADC is noisy enough to wobble the last digit.
  uint32_t mv = 0;
  for (int i = 0; i < 16; i++) mv += analogReadMilliVolts(pin);
  return (mv / 16.0) / 1000.0;
}

const char *advertises(float v) {
  if (v < OPEN_MAX)  return "nothing - this line is open";
  if (v < EDGE_1V5)  return "500 mA (default USB)";
  if (v < EDGE_3A)   return "1.5 A";
  return "3.0 A";
}

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println("CC watch - plug the breakout into a USB-C source");
}

void loop() {
  float v1 = readVolts(CC1_PIN);
  float v2 = readVolts(CC2_PIN);

  // The live CC is whichever one the cable actually connected.
  bool onCC1 = v1 > v2;
  float live = onCC1 ? v1 : v2;

  Serial.printf("CC1 %.2f V   CC2 %.2f V\n", v1, v2);

  if (live < OPEN_MAX) {
    Serial.println("  both lines open - no source, or no CC wire in the cable");
  } else {
    Serial.printf("  cable is on %s, source offers %s\n",
                  onCC1 ? "CC1" : "CC2", advertises(live));
  }

  delay(1000);
}