HW-038 Water Level Sensor with a Raspberry Pi Pico

// HW-038 Water Level Sensor on Raspberry Pi Pico: wiring and a free simulation at https://www.tinkered.ai/components/water-level-sensor-hw-038/raspberry-pi-pico
#include <hardware/gpio.h>

const int POWER_PIN = 0;    // HW-038 + on GP0: powered only to read (the traces corrode under constant DC)
const int SIGNAL_PIN = 28;  // HW-038 S on GP28 (ADC2)
const int DRY_BELOW = 100;  // under this the traces are dry

// 10-bit counts (arduino-pico's default) at 0, 25, 50, 75 and 100 % of the sensing length.
// + and the ADC reference are both 3.3 V here, so these tap-water figures from a 5 V Uno
// (both on 5 V) are a starting point only: record your own at known levels.
const int CAL[5] = { 335, 487, 565, 611, 641 };

int readSensor() {
  digitalWrite(POWER_PIN, HIGH);
  delay(10);                       // let S settle
  int raw = analogRead(SIGNAL_PIN);
  digitalWrite(POWER_PIN, LOW);
  return raw;
}

int levelPercent(int raw) {
  if (raw < DRY_BELOW) return 0;
  if (raw <= CAL[0]) return 1;
  for (int i = 1; i < 5; i++) {
    if (raw <= CAL[i]) return 25 * (i - 1) + (long)(raw - CAL[i - 1]) * 25 / (CAL[i] - CAL[i - 1]);
  }
  return 100;
}

void setup() {
  Serial.begin(9600);
  pinMode(POWER_PIN, OUTPUT);
  digitalWrite(POWER_PIN, LOW);
  gpio_set_drive_strength(POWER_PIN, GPIO_DRIVE_STRENGTH_12MA);   // the RP2040's default is 4 mA
  Serial.println("HW-038 ready");
}

void loop() {
  int raw = readSensor();
  Serial.print("raw ");
  Serial.print(raw);
  Serial.print("  level ");
  Serial.print(levelPercent(raw));
  Serial.println(" %");
  delay(1000);
}