i2c-moisture-sensor

I2C based soil moisture sensor. A continuation of the Chirp - plant watering alarm project. There is also an RS485 and an analog version available.

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.

Python library for Raspberry Pi

Göran Lundberg has released a Python library for Raspberry pi: https://github.com/ageir/chirp-rpi It has a very comprehensive documentation and covers a lot of functinality.

Some features:

• A trigger function to trigger all enabled sensors.
• Get soil moisture in percentage, requires calibration.
• Several temperature scales to choose from. Celcius, Farenheit and Kelvin.
• Temperature offset to calibrate temperature sensor.
• Change I2C address
• Deep sleep mode to save power.

Raspberry Pi examples

This is interface class provided by Daniel Tamm and Jasper Wallace

#!/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)
		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 "<Chirp sensor on bus %d, addr %d>" % (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

#!/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

#include <Wire.h>

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
}

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:

#include <Wire.h>
 
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 by Miriam Cox for Particle Photon boards.