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https://github.com/miceuz/i2c-moisture-sensor

I2C based soil moisture sensor
https://github.com/miceuz/i2c-moisture-sensor

avr i2c kicad sensor soil-moisture soil-moisture-sensor

Last synced: 5 days ago
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I2C based soil moisture sensor

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README 

          
# i2c-moisture-sensor



I2C based soil moisture sensor. A continuation of the [Chirp - plant watering alarm](https://github.com/Miceuz/PlantWateringAlarm) project. There is also an [RS485](https://github.com/Miceuz/rs485-moist-sensor) and an [analog](https://github.com/Miceuz/soil-moisture-sensor-analog) version available.



[![](https://d2ss6ovg47m0r5.cloudfront.net/badges/tindie-smalls.png)](https://www.tindie.com/products/2330/)



## I2C protocol

Available registers for reading and writing.



  Name | Register | R/W | Data length 

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

GET_CAPACITANCE   | 0x00 | (r) | 2

SET_ADDRESS       | 0x01 | (w) | 1

GET_ADDRESS       | 0x02 | (r) | 1

MEASURE_LIGHT     | 0x03 | (w) | 0

GET_LIGHT         | 0x04 | (r) | 2

GET_TEMPERATURE   | 0x05 | (r) | 2

RESET             | 0x06 | (w) | 0

GET_VERSION       | 0x07 | (r) | 1

SLEEP             | 0x08 | (w) | 0

GET_BUSY          | 0x09 | (r) | 1



GET_BUSY returns 1 if any measurement is in progress, 0 otherwise.



## How to interpret the readings



16bit values are returned most significant byte first.



Both light and moisture sensors give relative values. Meaning, more moisture will give you higher reading, more light, lower reading. They are not calibrated to any particular si units - this is up to you.



Moisture is somewhat linear. I test all sensors before shipping and they give about 290 - 310 in free air at 5V supply.



Temperature is in Celsius, value is in tenths of degrees Celsius. I.e. value 252 would mean 25.2°C.



I didn't measure linearity of the light sensor, it gives 65535 in a dark room away form desk lamp. When it's dark, it takes longer to measure light, reading the light register while measurement is in progress will return the previous reading. Be aware, light sensor is pretty noisy.



Temperature is measured by the thermistor on the body of the sensor. Calculated absolute measurement accuracy is better than 2%. 



Note Upon reading the moisture or temperature value, a value form the previous read command is returned and the new measurement is started. If you do rare measurements and want to act instantly, do two consecutive readings to get the most up to date data. Also you can read GET_BUSY register via i2c - it will indicate when the measurement is done. Basically the process goes like this: read from GET_CAPACITANCE, discard results, then read from GET_BUSY until you get '0' as an answer, then read form GET_CAPACITANCE again - the returned value is the soil moisture NOW.



### Python library for Raspberry Pi



*NOTE: if you experience problems on Raspberry Pi 3, slow down I2C bus speed by adding this line to /boot/config.txt:*

**dtparam=i2c1_baudrate=30000**



[Göran Lundberg](https://github.com/ageir) has released a Python library for Raspberry Pi: [https://github.com/ageir/chirp-rpi](https://github.com/ageir/chirp-rpi)

It has a very comprehensive documentation and covers a lot of functionality.



Some features:

* Uses a trigger function to trigger all enabled sensors. User selectable.

* Get soil moisture in percent (requires calibration) or capacitance value.

* Several temperature scales to choose from. Celcius, Fahrenheit and Kelvin.

* Offset to calibrate the temperature sensor.

* Measurement timestamps for all on board sensors.

* Built in support for changing the I2C address of the sensor.

* Deep sleep mode to conserve power.

* Calibration tool for soil moisture.



### Raspberry Pi examples



This is interface class provided by Daniel Tamm and Jasper Wallace

```python

#!/usr/bin/python

# cannot use python3 because smbus not working there

# Modified script from https://github.com/JasperWallace/chirp-graphite/blob/master/chirp.py

# by DanielTamm



import smbus, time, sys



class Chirp:

	def __init__(self, bus=1, address=0x20):

		self.bus_num = bus

		self.bus = smbus.SMBus(bus)

		self.address = address

    

	def get_reg(self, reg):

		# read 2 bytes from register

		val = self.bus.read_word_data(self.address, reg)

		# return swapped bytes (they come in wrong order)

		return (val >> 8) + ((val & 0xFF) << 8)



	def reset(self):

		# To reset the sensor, write 6 to the device I2C address

		self.bus.write_byte(self.address, 6)



	def set_addr(self, new_addr):

		# To change the I2C address of the sensor, write a new address

		# (one byte [1..127]) to register 1; the new address will take effect after reset

		self.bus.write_byte_data(self.address, 1, new_addr)

		# second request is required since FW 0x26 to protect agains spurious address changes

		self.bus.write_byte_data(self.address, 1, new_addr)

		self.reset()

		self.address = new_addr



	def moist(self):

		# To read soil moisture, read 2 bytes from register 0

		return self.get_reg(0)



	def temp(self):

		# To read temperature, read 2 bytes from register 5

		return self.get_reg(5)



	def light(self):

		# To read light level, start measurement by writing 3 to the

		# device I2C address, wait for 3 seconds, read 2 bytes from register 4

		self.bus.write_byte(self.address, 3)

		time.sleep(1.5)

		return self.get_reg(4)



	def __repr__(self):

		return "" % (self.bus_num, self.address)



if __name__ == "__main__":

	addr = 0x20

	if len(sys.argv) == 2:

		if sys.argv[1].startswith("0x"):

			addr = int(sys.argv[1], 16)

		else:

			addr = int(sys.argv[1])

	chirp = Chirp(1, addr)



	print chirp

	print "Moisture\tTemperature\tBrightness"

	while True:

		print "%d\t%d\t%d" % (chirp.moist(), chirp.temp(), chirp.light())

		time.sleep(1)

```



This is another RasPi example provided by user *krikk*

```python

#!/usr/bin/python



#https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code/tree/master/Adafruit_I2C

from Adafruit_I2C import Adafruit_I2C

from time import sleep, strftime

from datetime import datetime

deviceAddr = 0x20



i2c = Adafruit_I2C( deviceAddr, -1, False )



#to change adress

#i2c.write8( 1, 0x22 )



#reset sensor, we need this otherwise i get inconsistent light reading in the dark...

i2c.write8( deviceAddr, 0x06 )

sleep(5)



i2c.write8(deviceAddr, 3)

sleep(3)

light = i2c.readU16(4, False)

temp = i2c.readS16(5, False)/float(10)

moisture = i2c.readU16(0, False)

print "Temperature\tMoisture\tBrightness"

print str(temp) + ":" + str(moisture) + ":" + str(light)

```



### Arduino library

Ingo Fischer has written an Arduino library for the sensor, it has a couple of ready made examples: https://github.com/Apollon77/I2CSoilMoistureSensor 



Below are old examples for bare-bones Arduino illustrating a basic I2C use.



### Arduino example

```arduino

#include 



void writeI2CRegister8bit(int addr, int value) {

  Wire.beginTransmission(addr);

  Wire.write(value);

  Wire.endTransmission();

}



unsigned int readI2CRegister16bit(int addr, int reg) {

  Wire.beginTransmission(addr);

  Wire.write(reg);

  Wire.endTransmission();

  delay(20);

  Wire.requestFrom(addr, 2);

  unsigned int t = Wire.read() << 8;

  t = t | Wire.read();

  return t;

}



void setup() {

  Wire.begin();

  Serial.begin(9600);

  writeI2CRegister8bit(0x20, 6); //reset

}



void loop() {

  Serial.print(readI2CRegister16bit(0x20, 0)); //read capacitance register

  Serial.print(", ");

  Serial.print(readI2CRegister16bit(0x20, 5)); //temperature register

  Serial.print(", ");

  writeI2CRegister8bit(0x20, 3); //request light measurement 

  Serial.println(readI2CRegister16bit(0x20, 4)); //read light register

}

```

### Note for ESP8266 based systems

In some cases the default ESP8266 Arduino I2C library has the clock stretching timeout set too low. If you experience intermittent communication, add this to your code:

```

Wire.setClockStretchLimit(2500)

```

### Micropython

Micropython library is available here: [https://github.com/scopelemanuele/pyChirpLib](https://github.com/scopelemanuele/pyChirpLib)



## Address change example

By default the sensor comes with 0x20 set as an address, this is an example on how to change address for indivitual sensor:

```arduino

#include 

 

void writeI2CRegister8bit(int addr, int reg, int value) {

  Wire.beginTransmission(addr);

  Wire.write(reg);

  Wire.write(value);

  Wire.endTransmission();

}

 

void writeI2CRegister8bit(int addr, int value) {

  Wire.beginTransmission(addr);

  Wire.write(value);

  Wire.endTransmission();

}

 

void setup() {

  Wire.begin();

  Serial.begin(9600);

                                       //talking to the default address 0x20

  writeI2CRegister8bit(0x20, 1, 0x21); //change address to 0x21

  writeI2CRegister8bit(0x20, 6);       //reset

  delay(1000);                         //give it some time to boot

}

 

/*loop scans I2C bus and displays foud addresses*/ 

void loop()

{

  byte error, address;

  int nDevices;

 

  Serial.println("Scanning...");

 

  nDevices = 0;

  for(address = 1; address < 127; address++ )

  {

    // The i2c_scanner uses the return value of

    // the Write.endTransmisstion to see if

    // a device did acknowledge to the address.

    Wire.beginTransmission(address);

    error = Wire.endTransmission();

 

    if (error == 0)

    {

      Serial.print("I2C device found at address 0x");

      if (address<16)

        Serial.print("0");

      Serial.print(address,HEX);

      Serial.println("  !");

 

      nDevices++;

    }

    else if (error==4)

    {

      Serial.print("Unknow error at address 0x");

      if (address<16)

        Serial.print("0");

      Serial.println(address,HEX);

    }    

  }

  if (nDevices == 0)

    Serial.println("No I2C devices found\n");

  else

    Serial.println("done\n");

 

  delay(5000);           // wait 5 seconds for next scan

}

```

### Particle Photon



There is a great [tutorial](ParticlePhoton-tutorial.md) by Miriam Cox for Particle Photon boards. Also there is a [library available](https://github.com/VintageGeek/I2CSoilMoistureSensor) by Mike.



## Links and mentions



* A [video from Growing Robot](https://www.youtube.com/watch?v=rB4vS7I0euA) about using the sensors with Raspberry Pi

* A [complete Open Source logging solution](https://git.jeelabs.org/jcw/zelkova) employing a batch of 40 sensors in Crete for tree monitoring

* [Chirp - Wemos - Azure bridge](https://github.com/korpiq/chirp-wemos-meter) ESP8266 based system that pushes sensor data to Azure cloud serivices.