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

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

void loop() {
  // discharge
  pinMode(RX_PIN, OUTPUT);
  digitalWrite(RX_PIN, LOW);
  digitalWrite(TX_PIN, LOW);
  delayMicroseconds(20);

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

  int raw = analogRead(RX_PIN);
  digitalWrite(TX_PIN, LOW);

  Serial.println(raw);
  delay(5);
}