Moisture Sensor With ESP8266 - Email notifier

In this little project we will use a cheap soil moisture sensor to monitor when a plant requires more water. This sensor will be connected to an ESP8266 that will check the humidity periodically to alert us via email and blinking a led alarm. The sketch will have some configurable parameters over the Internet, like setting led alarm state (enable/disable, frequency), changing the hysteresis period, or checking the water state.

Required components

• ESP8266. In this project it is used a NodeMCU, but any other network enabled device can be used by adapting the code a little.

• Soil Moisture sensor. It is used a cheap one from AliExpress

• One led for blinking when there is no water.

• Arduino IDE with thinger.io library installed and support for the ESP8266 board.

This is the moisture sensor used in the project. Is a cheap one from AliExpress.

Wiring

The wiring for this project is so easy. The moisture sensor output (digital) is connected to D1 of the Node MCU board, while the alarm led is connected to D2.

Source Code

#include 
#include 
#include 
// thinger.io config
#define USER_ID "your_user_id"
#define DEVICE_ID "your_device_id"
#define DEVICE_CREDENTIAL "your_device_credential"
#define ALARM_ENDPOINT "your_alarm_endpoint"
// wifi config
#define WIFI_SSID "your_wifi_ssid"
#define WIFI_WPA2_PASSWORD "your_wifi_password"
// sensor/led pins
#define SENSOR_PIN D1
#define LED_PIN D2
ThingerWifi thing(USER_ID, DEVICE_ID, DEVICE_CREDENTIAL);
typedef enum WaterState{
 WATER,
 START_DETECTING_NO_WATER,
 NO_WATER
};
WaterState waterState = WATER;          // current water state
bool showLedAlarm = true;               // control led alarm on/off
unsigned long ledAlarmInterval = 500;   // led alam blink frequency
unsigned long previousMillis = 0;       // util for hysteresis and blink
unsigned long timeWithoutWater = 0;     // for hysteresis time
unsigned long hysteresisTime = 60000;   // one minute
int ledState = LOW;                     // current led alarm state
void setup() {
 // set pinmode for led alarm and humidity reader
 pinMode(SENSOR_PIN, INPUT);
 pinMode(LED_PIN, OUTPUT);
 // add wifi connection
 thing.add_wifi(WIFI_SSID, WIFI_WPA2_PASSWORD);
 // allow reading plant water/humidity
 thing["water"] >> [](pson& out){ out = !digitalRead(SENSOR_PIN); };
 // allow activating and deactivating led alarm remotelly
 thing["led_alarm"]["show"] << [](pson& in){ 
   if(in.is_empty()) in = showLedAlarm;
   else showLedAlarm = in;
 };
 // allow changing led alarm frequency
 thing["led_alarm"]["freq"] << [](pson& in){ 
   if(in.is_empty()) in = ledAlarmInterval;
   else ledAlarmInterval = in;
 }; 
 // allow changing hysteresisTime remotelly
 thing["hysteresis"] << [](pson& in){ 
   if(in.is_empty()) in = hysteresisTime;
   else hysteresisTime = in;
 };
}
void loop() {
 thing.handle();
 // read water value
 bool water = !digitalRead(SENSOR_PIN);
 
 if(water){
   if(waterState!=WATER){
     digitalWrite(LED_PIN, LOW); // turn off led alarm
     waterState = WATER; // reset water state
   }
 }else{
    unsigned long currentMillis = millis();
    switch(waterState){
       case WATER:
           timeWithoutWater = 0;
           previousMillis = currentMillis;
           waterState = START_DETECTING_NO_WATER;
         break;
       case START_DETECTING_NO_WATER:
         timeWithoutWater += (currentMillis - previousMillis);
         previousMillis = currentMillis;
         // only notify after a hysteresis time to prevent drifts in sensor reading
         if(timeWithoutWater>=hysteresisTime){
           waterState = NO_WATER;
           thing.call_endpoint(ALARM_ENDPOINT);
         }
         break;
       case NO_WATER:
         if(currentMillis - previousMillis > ledAlarmInterval) {
           previousMillis = currentMillis;   
           ledState = ledState == LOW ? HIGH & showLedAlarm : LOW;
           digitalWrite(LED_PIN, ledState);
         }
         break;
    }
 }
}