Capacitive Soil Moisture v1.2 with a Raspberry Pi Pico

// Capacitive Soil Moisture v1.2 on Raspberry Pi Pico: wiring and a free simulation at https://www.tinkered.ai/components/capacitive-soil-moisture-v12/raspberry-pi-pico
// Capacitive soil moisture v1.2 on a Raspberry Pi Pico: AOUT on GP28, VCC on 3V3.

const int SOIL_PIN = 28;          // GP28 (ADC2)
const float ADC_VREF = 3.3;       // the Pico's ADC reference: its 3.3 V rail
const float ADC_STEPS = 4096.0;   // 12 bits, set in setup() (arduino-pico defaults to 10)

// AOUT in air (dry) and in water (wet). 3.0 V and 1.2 V are the usual 5 V figures; on a 3.3 V
// supply the probe reads lower, so put your own two readings here.
const float DRY_V = 3.0;
const float WET_V = 1.2;

void setup() {
  Serial.begin(9600);
  analogReadResolution(12);
}

void loop() {
  float volts = analogRead(SOIL_PIN) * ADC_VREF / ADC_STEPS;
  int moisture = round((volts - DRY_V) * 100.0 / (WET_V - DRY_V));
  moisture = constrain(moisture, 0, 100);
  Serial.print("AOUT: ");
  Serial.print(volts, 2);
  Serial.print(" V | Moisture: ");
  Serial.print(moisture);
  Serial.println(" %");
  delay(500);
}