Required parts

* A N-type mosfet (We've used a HUF75545P3 mosfet)

* A 1KOhm resistor for use with the pump MOSFET

Optional parts

* A 1KOhm resistor per moisture sensor (only needed for the sensors without built-in transistor)

* A 1KOhm resistor for the float sensor (the internal pull-up feature that most Arduino boards have can be used as well)


This is what our prototype looks like:


Now that we connected our water pump to Homey we can automatically water our plants, but what about times when the tank becomes empty without us noticing?

To make sure that we are notified of an empty tank and to prevent the pump from running without water (to avoid damage to the pump) we added a float sensor to our setup. The float sensor we bought works as a switch. We suspended the float sensor in our water tank at the correct height by connecting it to a piece of coated iron wire which we cut to length and stuck to the top of the jerrycan with some tape.


Adding the float sensor to our Arduino project is suprisingly simple. The Arduino Uno on which we based this project has an internal pull-up resistor for all it's pins. This means that a resistor in the Arduino can pulls the input to the supply voltage, while the external sensor (which acts like a switch) just pulls the pin down by connecting it to ground.

So the only connections needed to make the float work are as follows:

| Float pin | Arduino pin |

|-------------|------------------|

| Wire 1 | Pin 3 |

| Wire 2 | Ground |

To read the float sensor the pin has to be configured as an input with pull-up enabled.

pinMode(3, INPUT_PULLUP);

This exposes the float sensor both as a trigger and as a condition. Additionally it prevents the pump from running when the tank is empty.

Should you want to replicate this on a platform that does not have internal pull-up support then you could replace the functionality using a resistor.

In that case you would still connect the sensor like described earlier, however you would need to add a resistor (with a value of for example 1KOhm) between the input pin on the Arduino and the 5v (or 3.3v, depening on the I/O voltage of your board) supply pin. For most Arduino boards the I/O voltage is 5 volt and for most ESP8266 and ESP32 boards the I/O voltage is 3.3v. Check the I/O voltage before connecting the resistor, for connecting the resistor to the wrong supply voltage could cause damage to your board.

When using an external pull-up resistor the pinMode statement would become like this:

pinMode(3, INPUT);

By adding the moisture sensor as a trigger a flow is triggered every time the moisture level changes. This can be used to implement a flow that checks if the moisture level changed below a threshold, allowing Homey to start the pump when necessary. Another approach might be checking of the moisture level as a condition by a flow that is triggered by a time interval, allowing you to make sure the pump isn't started too often.

#include <ESP8266WiFi.h>

#include <WiFiClient.h>

#define PIN_DHT D5

unsigned long previousMillis = 0;

void wifi() {

if (WiFi.status() != WL_CONNECTED) {

WiFi.begin("<SSID>", "<PASSWORD>");

uint8_t timeout = 30;

while (WiFi.status() != WL_CONNECTED) {

delay(500);

Serial.print(".");

if (timeout<1) break;

}

if (WiFi.status() == WL_CONNECTED) {

//Print IP address

Serial.print("Connected to WiFi! (");

Serial.print(WiFi.localIP());

Serial.println(")");

}

}

}

Homey.addCapability("measure_temperature");

wifi();

Serial.print((int)temperature); Serial.print(" *C, ");

#define PIN_DHT 2

unsigned long previousMillis = 0;

Homey.addCapability("measure_temperature");

Serial.print((int)temperature); Serial.print(" *C, ");