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  • Author Author: anpivey
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Measuring Soil Moisture with the Wemos ESP 32

anpivey

Hi Everyone,

Today, we are going to see our plant needs to be watered with a Wemos ESP 32, a mh soil moisture sensor known as the flying fish and Wia.

If you haven’t already I suggest you go through the tutorial here about posting to Wia with your Wemos board. It details setting up the correct environment and libraries to complete this tutorial.

Connecting the hardware

  • Pin | Description
  • VCC - > +5 Volts Power Source
  • GND -> Ground or negative power source
  • DO -> Digital Output. (low when moisture exceeds threshold)</td>
  • A0 > Analog Output - 0 -4.2 volts. The lower the voltage, the greater the moisture

 

Connect the two pins on the probe to the plus and minus pins on the mh-senor.

image

Now we need to connect mh sensor to our Wemos in the following way

  • MH - > Wemos
  • VCC -> VCC
  • GND - > GND
  • A0 -> 35

Connect the Wemos board to the computer via USB and check lights on the sensor and the Wemos.

image

The Code

The code below is all you need to get the measurement of the voltage across the probe which can be translated into the percentage moisture of the soil.

#include <ArduinoJson.h>
#include <WiFi.h>
#include <ArduinoHttpClient.h>
#include <Arduino.h>




const char* ssid     = "your-wifi-ssid"; // Your WiFi ssid
const char* password = "your-wifi-password"; //Your Wifi password


// Get this sccret key from the wia dashboard. It should start with `d_sk`
const char* device_secret_key = "your-device-secret-key";


// Wia API parameters
char server[] = "api.wia.io";
char path[] = "/v1/events";
int port = 80;


WiFiClient client;
int status = WL_IDLE_STATUS;


StaticJsonBuffer<200> jsonBuffer;
HttpClient httpClient = HttpClient(client, server, port);
JsonObject& root = jsonBuffer.createObject();


const int INPUT_PIN = 23; 
const int ANALOG_PIN = 35;


void setup() {
  
  pinMode(INPUT_PIN, INPUT);
  
  // initialize serial communications and wait for port to open:
  Serial.begin(115200);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }
  WiFi.begin(ssid, password);
  Serial.print("Attempting to connect to SSID: ");
  Serial.print(ssid);
  // attempt to connect to WiFi network:
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    // Connect to WPA/WPA2 network. Change this line if using open or WEP  network:
    // wait 5 seconds for connection:
    delay(5000);
  }


  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());
  Serial.println("connecting...");
}


// Thing function runs continiously
void loop() {
  
  root["name"] = "moisture";
  root["data"] =  analogRead (ANALOG_PIN);


  // if you get a connection, report back via serial:
  if (client.connect(server, port)) {


    sendToWia(root);


  } else {
    // if you didn't get a connection to the server:
    Serial.println("connection failed");
  }
   delay(1000*15*60); // Wait for 15 minutes to post again
}


// Adds the correct headers for HTTP and sends Data to Wia
void sendToWia(JsonObject& data) {
  size_t len = data.measureLength();
  size_t size = len + 1;
  char json[size];
  httpClient.beginRequest();
  httpClient.post(path);
  httpClient.sendHeader("Content-Type", "application/json");
  httpClient.sendHeader("Content-Length", data.measureLength());
  httpClient.sendHeader("Authorization", "Bearer " + String(device_secret_key));
  httpClient.beginBody();
  data.printTo(httpClient);
  Serial.print("Posting ");
  data.printTo(Serial);
  Serial.println(" to Wia");
  httpClient.endRequest();


}

 

Replace the following values of the following variables names (Place the correct value between the quotation marks right of the variable names in the code):

  • ssid - with your WiFi network name.
  • password - with your WiFi network password.
  • device_secret_key with your device secret key from the Wia Dashboard (the one that begins with d_sk).

 

In the Arduino IDE:

  • Select the Wemos lollin32 board
  • Select the appropriate port
  • Click Sketch > Upload in the menu

 

Go to the Wia dashboard and view the events as the come in the Wia debugger.

image

 

Notifying you when your plant needs watering

Now we are going to set up a flow in the Wia flow studio that gives you a push notification when the moisture percent passes a certain threshold. The Wia app is required to send a push notification to your phone, it can be installed here for Android and here for ios.

Go to your Wia Dashboard and in the space you setup before, go to flow section in the left side bar and create a flow. You can name whatever you prefer.

image

In flow studio, drag an event node from the triggers section and:

  • Enter moisture as the the event name
  • Add the device that matches the one added to the code earlier

Drag a function node from the logic section and copy and paste the following code:

if (input.body) {


    if (input.body.data < 3000) {


        output.process = 0;  


    }


}


else {


    output.process = 0; 


}

The Output from the soil moisture sensor is a number between 0 and 4200 with zero being completely wet and 4200 being completely dry.

All the code above does is sets to not process the output when there is no input or if the input is less than 3000 (i.e The doesn't plant need watering)

Finally, and a notification node and enter The plant is needs watering in the text field so that Wia can send a notification to you when your plant needs watering.

image

Thats it! If you are having any problems, drop us a line below and we'll help you out.