Capacitive Soil Moisture v1.2 with an Arduino Uno

// Capacitive Soil Moisture v1.2 on Arduino Uno: wiring and a free simulation at https://www.tinkered.ai/components/capacitive-soil-moisture-v12/arduino-uno
// Capacitive soil moisture: analogRead + calibrated percent.
// Calibration constants are auto-selected per board (see the table above).

const int SOIL_PIN = A0;          // Arduino: A0-A5 | ESP32: an ADC1 GPIO (e.g. 34)

#if defined(ESP32)
const int DRY_VALUE = 3723;       // ~3.0V on a 12-bit ESP32 ADC (sensor in air)
const int WET_VALUE = 1489;       // ~1.2V (sensor in water)
#else
const int DRY_VALUE = 614;        // ~3.0V on a 10-bit Uno ADC (sensor in air)
const int WET_VALUE = 245;        // ~1.2V (sensor in water)
#endif

void setup() {
  Serial.begin(9600);
}

void loop() {
  int raw = analogRead(SOIL_PIN);
  // round() (not map(): map() truncates and reads ~1% low)
  int moisture = round((float)(raw - DRY_VALUE) * 100.0 / (WET_VALUE - DRY_VALUE));
  moisture = constrain(moisture, 0, 100);
  Serial.print("Raw ADC: ");
  Serial.print(raw);
  Serial.print(" | Moisture: ");
  Serial.print(moisture);
  Serial.println(" %");
  delay(500);
}