Plant sensor for Home Assistant on an ESP32-C3

// Home Assistant plant sensor: soil moisture and light, calibrated, with a thirsty alarm.
//
//   capacitive soil sensor on GPIO 3   wetter soil reads LOWER, which surprises everyone once
//   light module on GPIO 4             the LDR board's analog output, brighter reads lower
//   red LED on GPIO 19                 lights while the plant needs water
//
// A plant sensor is mostly calibration. The raw number means nothing until you
// have measured two points with your own sensor: the stake in dry air and the
// stake in a glass of water. Put those two readings in DRY_RAW and WET_RAW and
// the sketch maps everything between them to 0 to 100 percent, the same job
// ESPHome's calibrate_linear filter does.
//
// The thirsty alarm uses two thresholds, not one, so a reading that hovers near
// the line does not switch it on and off every few seconds.
//
// A battery sensor would read once and deep sleep for many minutes. Here it reads
// every 5 seconds so you can watch it, and stays awake. Mokxi has no MQTT broker:
// the sketch prints what it would publish and serves JSON at /state.

#include <WebServer.h>
#include <WiFi.h>

const int SOIL_PIN = 3;
const int LIGHT_PIN = 4;
const int THIRSTY_LED_PIN = 19;

// Your sensor's two calibration readings (0 to 4095 on the ESP32-C3).
const int DRY_RAW = 3164;  // in air
const int WET_RAW = 1576;  // in water
const int THIRSTY_BELOW = 30;  // percent
const int HAPPY_ABOVE = 40;    // percent

const unsigned long READ_EVERY_MS = 5000;

WebServer server(80);
int moisture = 0;
int lightLevel = 0;
bool thirsty = false;
unsigned long lastRead = 0;

void publish(const char *topic, int value) {
  Serial.print("publish home/plant/");
  Serial.print(topic);
  Serial.print(' ');
  Serial.println(value);
}

// The average of a few readings: a single ADC sample is noisy on real hardware.
int readAverage(int pin) {
  long total = 0;
  for (int i = 0; i < 8; i++) total += analogRead(pin);
  return total / 8;
}

void readPlant() {
  int raw = readAverage(SOIL_PIN);
  moisture = constrain(map(raw, DRY_RAW, WET_RAW, 0, 100), 0, 100);
  // The light module reads lower in more light; flip it so bigger means brighter.
  lightLevel = map(readAverage(LIGHT_PIN), 4095, 0, 0, 100);

  Serial.print("soil raw ");
  Serial.print(raw);
  Serial.print(" -> ");
  Serial.print(moisture);
  Serial.println("%");
  publish("moisture", moisture);
  publish("light", lightLevel);

  if (!thirsty && moisture < THIRSTY_BELOW) {
    thirsty = true;
    Serial.println("publish home/plant/thirsty ON");
  } else if (thirsty && moisture > HAPPY_ABOVE) {
    thirsty = false;
    Serial.println("publish home/plant/thirsty OFF");
  }
  digitalWrite(THIRSTY_LED_PIN, thirsty ? HIGH : LOW);
}

void sendState() {
  String json = "{\"moisture\":";
  json += String(moisture);
  json += ",\"light\":";
  json += String(lightLevel);
  json += ",\"thirsty\":";
  json += thirsty ? "true" : "false";
  json += "}";
  server.send(200, "application/json", json);
}

void setup() {
  Serial.begin(115200);
  pinMode(THIRSTY_LED_PIN, OUTPUT);

  Serial.println("Plant sensor: simulated WiFi, no MQTT broker in Mokxi.");
  WiFi.begin("Mokxi-Lab", "breadboard");
  while (WiFi.status() != WL_CONNECTED) {
    delay(250);
  }
  Serial.print("online at http://");
  Serial.print(WiFi.localIP());
  Serial.println("/state");
  server.on("/", sendState);
  server.on("/state", sendState);
  server.begin();
  readPlant();
  lastRead = millis();
}

void loop() {
  server.handleClient();
  if (millis() - lastRead >= READ_EVERY_MS) {
    lastRead = millis();
    readPlant();
  }
  delay(10);
}