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.
###Raspberry Pi example
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.