Soil moisture sensor

Authors

For more information contact Frederic Cherqui, Adam Simankowicz or Edmond Lascaris

Applications

Soil moisture of trees, garden beds and agriculture. Sensors originally deployed in Africa to educate farmers about irrigation of food crops

How the Soil moisture sensor works

• Soil moisture sensor circuit explained by Matthew Driver

Components

• Arduino MKR Zero microcontroller using two analog pins with 10 bit analog to digital converters (ADC).
• Two 10K 0.1% precision resistors
• Chameleon soil moisture sensor

Power supply voltage (Vcc)

• This design is independent of voltage.
• In this circuit the power will be supplied via a Pololu 5V step-up regulated supply.

Analog pins

• The analog pins on the Arduino microcontroller are dual purpose.
  • They can measure a voltage between 0 and Vcc (when their mode is set as an analog INPUT)
  • They can also but can also output Vcc (3.3 or 5V) or drain to ground (when their mode is set to digital OUTPUT) * Both of these states are set using the pinmode function in the Arduino code.

States

• To measure the soil moisture the sensor circuit is placed into three different states:
  • Forward current
  • Reverse current (the flow of electrons is reversed from the perspective of the sensor)
  • No current

Schematic

• A schematic of the soil moisture sensor circuit is shown below.
• Pin X and Pin Y are the two analog input pins on the Arduino microcontroller.

Excitation and and measuring (states applied)

Forward current flow

• To begin the measurement a Forward current is applied to the sensor
• The Forward current state is applied for 250us (microseconds) by setting the pins to:
  • pinMode(Pin_Y,INPUT)
  • pinMode(Pin_X,OUTPUT)
  • digitalWrite(Pin_X, HIGH)
• The voltage is then measured at pin Y and stored in a variable.

No current flow

• A No current state is then applied for 250us by setting the pins to:
  • digitalWrite(Pin X, LOW)
• The result is all pins are at ground so no current flows.
• Note that the INPUT pin acts as a drain, which is equivalent to ground.

Reverse current flow

• Then Reverse current state is then applied for 250us (microseconds) by setting the pins to:
  • pinMode(Pin_X,INPUT)
  • pinMode(Pin_Y,OUTPUT)
  • digitalWrite(Pin_Y, HIGH)
• The voltage is then measured at pin X and stored in variable.

Sensor resistance calculation

• The Arduino convert the analog input to a digital value between 0 and 1023 where 1023 is the Vcc voltage (5V), *
• Sensor Resistance = Rs = 10K * (1023 - Vs) / Vs
  • where Vs is the average of forward and reverse current values

• Temperature will change the measured value
• A simple formula allows for soil temperature changes to be corrected.
  • Formula: Ra = R0 * (1 + (Temp - 22) * 0 .018 )

• Lastly, the soil moisture resistance is converted to soil moisture tension and expressed in kPa pressure units.
• This is a measure of how much pressure plants need to apply to extract moisture from soil.
• The relationship is shown in the graph below.

Interpreting Soil Moisture sensor values

• The Soil Moisture Sensor measures how hard it is for plants to draw water from soil.
• This soil moisture sensor measures resistance and then converts this value to soil moisture tension in kPa.
• This higher the soil moisture tension (kPa), the harder it is for plants to extract moisture from the soil.

• Soil moisture tension from 20 - 30 kPa signifies wet soil - ideal for broccoli, celery, lettuce and onion
• Soil moisture tensions from 30 - 45 kPa is moist soil - ideal for beans, cabbage, carrot, capsicum, corn, cucumber, eggplant, melons, potato and tomato.
• Soil moisture tenions from 45 - 60 kPa is dry soil - ideal for beet, peas, wweet potato and pumpkin.

Software installation requirements

• Atom installed on PC or Mac with Pymakr package installed
• Arduino IDE installed

Parts list

Item description	Number	Supplier	Part number	URL	Cost	Notes
Solder-able Breadboard	2	Core Electronics	SKU: PRT-12070	https://core-electronics.com.au/solder-able-breadboard.html	$8.20	55mm x 80mm
Pycom LoPy4 (LoRaWAN)	1	Core Electronics	SKU: CE05399	https://core-electronics.com.au/pycom-lopy4.html	$68.95	Microcontroller with LoRa
Pycom Expansion Board 3.1	1	Core Electronics	SKU: CE05545	https://core-electronics.com.au/pycom-expansion-board-3-1.html	$35.95	Used to program LoPy4
Arduino MKR Zero	1	Core Electronics	SKU: ABX00012	https://core-electronics.com.au/arduino-mkr-zero-i2s-bus-sd-for-sound-music-digital-audio-data.html	$45.00	Used to measure soil moisture
DHT22 Temperature and Relative Humidity Sensor Module	1	Core Electronics	SKU: 018-DHT22	https://core-electronics.com.au/dht22-temperature-and-relative-humidity-sensor-module.html	$13.75	Temp precision +/-0.5degC
Temperature Sensor - Waterproof (DS18B20)	1	Core Electronics	SKU: SEN-11050	https://core-electronics.com.au/temperature-sensor-waterproof-ds18b20.html	$18.80	1-Wire interface library
Soil moisture sensor (calibrated) - Chameleon card 3 sensor pack	1	ViaShopCSIRO	3 sensor pack	https://viashop.csiro.au/chameleon-card-six-sensor-pack	$49.00	Soil moisture sensor
Electrolytic Decoupling Capacitors - 100uF/25V	1	Core Electronics	SKU: COM-00096	https://core-electronics.com.au/electrolytic-decoupling-capacitors-100uf-25v.html	$0.29	Used to block high voltage spikes
Pololu 5V Step-Up Voltage Regulator U1V11F5	1	Core Electronics	SKU: POLOLU-2562	https://core-electronics.com.au/pololu-5v-step-up-voltage-regulator-u1v11f5.html	$11.65	5V supply for sensors
Resistor 10K Ohm 1/4 Watt PTH - 20 pack (Thick Leads)	1	Core Electronics	SKU: PRT-14491	https://core-electronics.com.au/resistor-10k-ohm-1-4-watt-pth-20-pack-thick-leads.html	$2.05	Pack of 20 resistors
Hook-Up Wire - Assortment (Solid Core, 22 AWG)	1	Core Electronics	SKU: PRT-11367	https://core-electronics.com.au/hook-up-wire-assortment-solid-core-22-awg.html	$40.95	Solid core for wiring circuit
36-pin 0.1 Female header - pack of 5!	1	Core Electronics	SKU: ADA598	https://core-electronics.com.au/20-pin-0-1-female-header-pack-of-5.html	$6.30	Used for plugin components
10 Pcs 40 Pin Headers - Straight	1	Core Electronics	SKU: FIT0084	https://core-electronics.com.au/10-pcs-40-pin-headers-straight.html	$4.70	Used to make sensors plugin
Holman 100mm PVC DWV Push On Cap	1	Bunnings	DWVF0198	https://www.bunnings.com.au/holman-100mm-pvc-dwv-push-on-cap_p4770360	$3.30	End caps for sensor housing
Holman 100mm x 3m PVC DWV Pipe	1	Bunnings	DWV1003	https://www.bunnings.com.au/holman-100mm-x-3m-pvc-dwv-pipe_p4770345	$33.00	Cut in store for easier transport
Selleys 310g Clear Glass Silicone Sealant	1	Bunnings	Model no 9300697100382	https://www.bunnings.com.au/selleys-310g-clear-glass-silicone-sealant_p1234951	$15.00	Used with caulking gun
18650 2600mAh Li-ion Protected Battery	1	Jaycar	CAT.NO: SB2299	https://www.jaycar.com.au/18650-2600mah-li-ion-protected-battery/p/SB2299	$21.95	Inbuilt safety protection
Single 18650 Battery Holder	1	Jaycar	CAT.NO: PH9205	https://www.jaycar.com.au/single-18650-battery-holder/p/PH9205	$3.25	Battery holder
Dual-Channel Li-ion / Ni-MH Battery Charger	1	Jaycar	CAT.NO: MB3635	https://www.jaycar.com.au/dual-channel-li-ion-ni-mh-battery-charger/p/MB3635	$39.95	Only one required for all projects
MOLEX 211140-0100.. 868/915MHZ FLEXIBLE ANTENNA100MM CABLE	1	Element-14	Order code 3225220	https://au.element14.com/molex/211140-0100/868-915mhz-flexible-antenna100mm/dp/3225220?ost=molex++211140-0100..++868%2F915mhz+flexible+antenna100mm+cable	$2.84	Attached to LoPy4
Through Hole Resistor, 10 kohm, CMF, 500 mW, ± 0.1%, Axial Leaded, 250 V	4	Element-14	Order code 3596907	https://au.element14.com/vishay/cmf5510k000beea/res-10k-0-5w-axial-metal-film/dp/3596907?ost=vishay++cmf5510k000beea	$1.56	High precision resistor for voltage divider
P9406 • 6 Pin 5A Screw-On Female Line IP66 Waterproof Socket	1	Altronics	Code: P9406	https://www.altronics.com.au/p/p9406-amphenol-ltw-6-pin-5a-screw-on-female-line-ip66-waterproof-socket/	$23.50	Connected to sensor housing
P9416 • 6 Pin 5A Screw-On Male Chassis IP67 Waterproof Plug	1	Altronics	Code P9416	https://www.altronics.com.au/p/p9416-amphenol-ltw-6-pin-5a-screw-on-male-chassis-ip67-waterproof-plug/	$17.25	Connected to sensor

Photos of completed circuit board

• Aerial view of Pycom LoPy4 board showing battery supply, soil moisture sensor and external temperature sensor.

• Close up view of Pycom LoPy4 board.

• Close up view of sensor board without LoPy4 microcontroller.

• Close up view of Arduino MKR Zero microcontroller.

• Close up view of Arduino MKR Zero sensor board without Arduino.

• Back of Pycom LoPy4 board (top) and Arduino MKR Zero (bottom).
• Note the location and orientation of locator pins.

Electronic circuit construction for LoPy4

Pycom LoPy4

• LED on LoPy4 nearest top end of board.
• Cut female header pins to 14 pin length (x2)
• Solder from pins C10 to C23 and from pins H10 to H23
• VIN (3.5-4.2V direct from battery rail) from positive rail nearest to J to pin J10
• GND from negative rail nearest to J to pin J11
• 3.3V supply from pin I12

Voltage divider circuit

• 10k ohm high precision resistors x 2
• I16 to positive rail nearest to J
• J16 to negative rail nearest to J

Power supply

• Use either 3 x 1.2V Panasonic eneloop Ni-MH batteries
• Or use 1 x 3.7V Li-Ion battery
• Attach positive and negative rails nearest to J

DHT22 temperature and humidity sensor

• C30 to Pin 1 VCC (Power Supply)
• C29 to Pin 2 DATA (The data signal)
• C28 to Pin 3 NULL (Do not connect)
• C27 to Pin 4 GND (Ground)
• 10k ohm resistor (low precision) D30 to E29
• GND connection from E27 to negative rail nearest to J
• DATA connection from D29 to D21
• VCC connection from E30 to G4

Pololu 5V Step-Up Voltage Regulator U1V11F5

• Cut female header pins to 4 pin length
• Solder from pins H1 to H4
• Solder right angle male header pins to Regulator so board stands upright (supplied with regulator)
  • H1 to shutdown (SHDN)
  • H2 to input voltage (VIN) - from battery
  • H3 to ground (GND)
  • H4 to output voltage (VOUT) - 5V regulated
• 10k ohm pull-down resistor (low precision) J1 to negative rail nearest to J
• GND connection from J3 to negative rail nearest to J
• Electrolytic Decoupling Capacitor positive terminal J2
• Electrolytic Decoupling Capacitor negative terminal J3
• VIN (3.3V from LoPy4) from I12 to I2
• SHDN (shutdown) pin connected from E20 to F1

DS18B20 external temperature sensor

• Cut female header pins to 3 pin length
• Solder from pins D1 to D3
  • D1 to DATA
  • D2 to VCC
  • D3 to GND
• Solder right angle male header pins to temperature sensor leads
• GND connection from pin A3 to negative rail nearest to A
  • negative rail connected to D27
• DATA connection from pin E1 to E23
• VCC (5V regulated supply) connection from pin E2 to I4
  • 5V rail connected to F4
• 10k ohm pull-up resistor (low precision) from pin B1 to C2

UART connector

• UART connector to receive soil moisture sensor data from Arduino MKR Zero
• UART connection on LoPy4 from pin A15 to A5

Underboard connector pins for LoPy4 board

• two-pin connector (+ and - rails) on rail nearest to A
  • one close to pin A1
  • second close to pin A19/A20

• two-pin connector (both within - rail) on rail nearest to J
  • one close to pin J7
  • second close to pin J26

• UART connector pin B5 and C5 to receive soil moisture sensor data from Arduino

Electronic circuit construction for Arduino MKR Zero

Arduino MKR Zero

• LED on LoPy4 nearest top end of board.
• Cut female header pins to 14 pin length (x2)
• Solder from pins I8 to I21 and from pins C8 to C21
• VIN (3.5-4.2V direct from battery rail) from positive rail nearest to A to pin A9
• GND from negative rail nearest to A to pin A11
• UART transmission from pin B13 to A5

Soil moisture sensor

• 10k ohm high precision resistor (0.1%) from negative rail nearest to J to pin J10
• 10k ohm high precision resistor (0.1%) from negative rail nearest to J to pin J11
• Soil moisture sensor connection lead F10 to external plug
• Soil moisture sensor connection lead F11 to external plug
• GND bridging lead from negative rail (close to pin J4) to opposite negative rail (close to pin A4)

Underboard connector pins for Arduino board

• two-pin connector (+ and - rails) on rail nearest to A
  • one close to pin A1
  • second close to pin A19/A20

• two-pin connector (both within - rail) on rail nearest to J
  • one close to pin J7
  • second close to pin J26

• UART connector pin B5 and C5 to receive soil moisture sensor data from Arduino

MicroPython code for Pycom LoPy4 microcontroller

• There are several different code segments used on the Pycom LoPy4 microcontroller to monitor temperature.
  • boot.py - bootstrap program that runs first.
  • main.py - main program where program code is contained
  • pymakr.conf - configuration file for Atom and Pymakr package
  • lib - directory that contains additional library files
    • config.py - list of static variables
    • dth.py - library for DHT22 internal temperature sensor
    • lora.py - library for LoRa. Contains private keys
    • onewire.py - onewire library to communicate with DS18B20 external temperature sensor

boot.py

# boot.py -- run on boot-up

import pycom
from machine import UART
import machine
import os
from network import Bluetooth
from network import WLAN

if pycom.heartbeat() == True:
    pycom.heartbeat(False)

if pycom.wifi_on_boot() == True:
  pycom.wifi_on_boot(False)

#wlan = WLAN()
#wlan.deinit()

bluetooth = Bluetooth()
bluetooth.deinit()

uart = UART(0, baudrate=115200)
os.dupterm(uart)

machine.main('main.py')

main.py

# main.py
#!/usr/bin/env python

import binascii #module that makes conversion between binary and Ascii
import config
from dth import DTH # internal temp/humidity sensor library
import gc # garbage collection
from lora import LoraAU915
import machine
from machine import Pin
from machine import ADC
from machine import UART  # UART serial communcation between LoPy and Arduino MKR
from onewire import DS18X20 # external temp sensor library
from onewire import OneWire # library to communicate with external temp sensor
import pycom # to control led lights on LoPy
import network
import socket # for LoRa communcations
import time
import ustruct
import utime

#INIT EVERYTHING
sleep_duration = 600  # in seconds (10 minutes)
pycom.rgbled(config.GREEN)

# power up sensors
sensor_power = Pin(config.POWER_PIN, mode=Pin.OUT)  # power for DHT22
sensor_power.value(1)  # power up
time.sleep(2)   # wait 2 seconds to stabilise

print("starting main")
pycom.rgbled(config.OFF)

# voltage divider setup to monitor battery voltage
adc = ADC()
time.sleep(2)   # wait 2 seconds to stabilise

# garbage collection enabled
gc.enable()

# config LoRa communications
s = LoraAU915.setupLora()

#DS18B20 external temperature sensor
ow = OneWire(Pin('P12'))
temp = DS18X20(ow)

while True:
    sensor_power.value(1)  # power up all sensors

    time.sleep(1)
    pycom.rgbled(config.ORANGE)
    time.sleep(1)
    pycom.rgbled(config.OFF)


    # TEMPERATURE AND HUMIDITY OF AMBIENT AIR
    j = 0
    DHT_temperature = 0.0
    DHT_humidity = 0.0
    th = DTH(config.DHT22_DATA,1)
    time.sleep(1)
    while j < 5:
        result = th.read()
        if result.temperature != 0:
            print("temperature is not zero - breaking from while loop")
            pycom.rgbled(config.GREEN)
            time.sleep(1)
            pycom.rgbled(config.OFF)
            DHT_temperature = result.temperature
            DHT_humidity = result.humidity
            break
        time.sleep(1)
        j += 1
        print("Error code %d" % result.error_code)
        print(j)
    print("Temperature = = %.2f C" % DHT_temperature)
    print("Humidity = %.2f %%" % DHT_humidity)


    # BATTERY
    meanbatt=0
    j=0
    while j < 5:
        utime.sleep(0.2)
        batt = adc.channel(attn=3, pin=config.VOLTMETER)
        meanbatt += batt.voltage()/1000
        j += 1
    batt_volt = (meanbatt/j)*config.BATCOEFF #multiplcator coef to adjust the real value of the battery voltage
    print("Battery voltage = %.2f V" % batt_volt)
    pycom.rgbled(config.ORANGE)
    time.sleep(1)
    pycom.rgbled(config.OFF)


    #DS18B20 TEMPERATURE SENSOR
    #https://docs.pycom.io/tutorials/hardware/owd/#app

    #Also note - needed to add a 10k resistor pull up on the board
    #Internal pull up resistor was not sufficient
    #used this reference for Raspberry Pi circuit which includes 5k to 10k pull up resistor
    #https://www.circuitbasics.com/raspberry-pi-ds18b20-temperature-sensor-tutorial/



    temp.start_conversion()
    time.sleep(1)
    soil_temp = temp.read_temp_async()
    time.sleep(1)

    if soil_temp != None:
        print("Soil temperature = %.2f C" % soil_temp)
    else:
        print("No data received from soil temp probe")
        pycom.rgbled(config.RED)
        time.sleep(1)
        pycom.rgbled(config.OFF)
        soil_temp = 0.0

    # SOIL MOISTURE SENSOR
    # Temperature compensation formula for temperature probe
    #Formula: Ra = R0 * (1 + (Temp - 22) * 0 .018 ) with:
    #Ra: adjusted resistance,
    #R0: measured resistance
    #Temp in degree celsius, soil temperature
    # this uses the UART_1 default pins for TXD and RXD (``P3`` and ``P4``)

    j = 0
    buffer = ""
    soil = 0
    #soil_temp = 0
    uart = UART(1, baudrate=9600)
    time.sleep_ms(500)  # helps with initialisation
    while j<15:
        print(j)
        if uart.any() > 0:
            print(uart.any())
            time.sleep(1)
            buffer = uart.readline()
            if "\n" in buffer:
                print(buffer)
                # may need buffer.decode().strip() to get soil moisture
                str_buffer = buffer.decode()
                string_list = str_buffer.split(",")

                #soil_temp = int(string_list[0])
                soil = int(string_list[1])

                pycom.rgbled(config.BLUE)
                time.sleep(1)
                pycom.rgbled(config.OFF)
                break
        time.sleep_ms(1000)
        j += 1
    #print("Soil temperature is {}".format(soil_temp))
    print("Soil moisture is {}".format(soil))

    soil_t = int(soil)
    soil_temp_t = int(soil_temp*100)
    batt_volt_t = int(batt_volt*100)
    sens_temp = int(DHT_temperature*100)
    sens_humi = int(DHT_humidity*100)


    # converting 2 byte values into single bytes for transmission
    soil1 = int(soil_t//256)
    soil2 = int(soil_t%256)
    soil_temp1 = int(soil_temp_t//256)
    soil_temp2 = int(soil_temp_t%256)
    batt1 = int(batt_volt_t//256)
    batt2 = int(batt_volt_t%256)
    temp1 = int(sens_temp//256)
    temp2 = int(sens_temp%256)
    humi1 = int(sens_humi//256)
    humi2 = int(sens_humi%256)


    print("sending to TTN")
    s.setblocking(True)
    print(soil1, soil2, soil_temp1, soil_temp2, batt1, batt2, temp1, temp2, humi1, humi2)
    s.send(bytes([soil1, soil2, soil_temp1, soil_temp2, batt1, batt2, temp1, temp2, humi1, humi2]))
    s.setblocking(False)
    pycom.rgbled(config.BLUE)
    time.sleep(1)
    pycom.rgbled(config.OFF)

    # Save LoRa settings before deep sleep
    LoraAU915.saveLora()
    print("going to sleep")
    sensor_power.value(0)  # power down
    time.sleep(2)   # wait 2 seconds to stabilise

    # note that batt_volt has been multiplied by 100 for transmission
    # note increased min voltage to force deep sleep if running on batteries
    # bat voltage normally above 6V when connected to Atom
    print("batt_volt {}".format(batt_volt))
    if (batt_volt > 6.0):
        # to minimise writes to onboard memory and for teaching
        sleep_duration = 600  # sleep for 10 minutes
        print("Time delay sleep only")
        time.sleep(sleep_duration) # sleep in seconds
    else:
        sleep_duration = 3600  # sleep for 60 minutes
        print("Sleep using deepsleep")
        machine.deepsleep(1000 * sleep_duration)   # deepsleep in ms

pymakr.conf

{
    "address": "COM10",
    "username": "micro",
    "password": "python",
    "sync_folder": "",
    "sync_file_types": [
        "py",
        "txt",
        "log",
        "json",
        "xml",
        "html",
        "js",
        "css",
        "mpy",
        "pem",
        "cet",
        "crt",
        "key"
    ],
    "sync_all_file_types": false,
    "open_on_start": true,
    "safe_boot_on_upload": false,
    "py_ignore": [],
    "fast_upload": false
}

config.py

########################
# CONFIG FILE !!!!
########################

# PINs
POWER_PIN = 'P9'  # pin that powers enable pin on 5V Pololu regulator
DHT22_DATA = 'P10'  # pin that receives data from internal temp/humidity sensor

VOLTMETER='P20' # pin connected to voltage divider
BATCOEFF = 2.0 # to calculate the real voltage

# led colors
OFF = 0x000000
WHITE=0xFFFFCC
RED = 0xff0000
BLUE = 0x0000ff
GREEN = 0x00ff00
YELLOW = 0x7f7f00
PURPLE = 0x7f007f
ORANGE = 0xFF9900

dth.py

# dth.py
import time
import pycom
from machine import enable_irq, disable_irq,  Pin

# DHT22 sensor pins - when sensor lying down

#1 - VCC - red wire Connect to 3.3 - 5V power. Sometime 3.3V power isn't enough in which case try 5V power.
#2 - Data out - white or yellow wire
#3 - Not connected
#4 - Ground - black wire

# Note - 10 Kohm resistor between VCC and the data pin
# current draw 1.5mA - pycom advise up to 6mA per pin

class DTHResult:
    'DHT sensor result returned by DHT.read() method'

    ERR_NO_ERROR = 0
    ERR_MISSING_DATA = 1
    ERR_CRC = 2

    error_code = ERR_NO_ERROR
    temperature = -1
    humidity = -1

    def __init__(self, error_code, temperature, humidity):
        self.error_code = error_code
        self.temperature = temperature
        self.humidity = humidity

    def is_valid(self):
        return self.error_code == DTHResult.ERR_NO_ERROR

class DTH:
    'DHT sensor (dht11, dht21,dht22) reader class for Pycom'

    #__pin = Pin('P3', mode=Pin.OPEN_DRAIN)
    __dhttype = 0

    def __init__(self, pin, sensor=0):
        self.__pin = Pin(pin, mode=Pin.OPEN_DRAIN)
        self.__dhttype = sensor
        self.__pin(1)
        time.sleep(1.0)

    def read(self):
        # pull down to low
        self.__send_and_sleep(0, 0.019)
        data = pycom.pulses_get(self.__pin,100)
        self.__pin.init(Pin.OPEN_DRAIN)
        self.__pin(1)
        #print(data)
        bits = []
        for a,b in data:
        	if a ==1 and 18 <= b <= 28:
        		bits.append(0)
        	if a ==1 and 65 <= b <= 75:
        		bits.append(1)
        #print("longueur bits : %d " % len(bits))
        if len(bits) != 40:
            return DTHResult(DTHResult.ERR_MISSING_DATA, 0, 0)
        #print(bits)
        # we have the bits, calculate bytes
        the_bytes = self.__bits_to_bytes(bits)
        # calculate checksum and check
        checksum = self.__calculate_checksum(the_bytes)
        if the_bytes[4] != checksum:
            return DTHResult(DTHResult.ERR_CRC, 0, 0)
        # ok, we have valid data, return it
        [int_rh, dec_rh, int_t, dec_t, csum] = the_bytes
        if self.__dhttype==0:		#dht11
            rh = int_rh 		#dht11 20% ~ 90%
            t = int_t 	#dht11 0..50°C
        else:			#dht21,dht22
            rh = ((int_rh * 256) + dec_rh)/10
            t = (((int_t & 0x7F) * 256) + dec_t)/10
            if (int_t & 0x80) > 0:
                t *= -1
        return DTHResult(DTHResult.ERR_NO_ERROR, t, rh)

    def __send_and_sleep(self, output, mysleep):
        self.__pin(output)
        time.sleep(mysleep)

    def __bits_to_bytes(self, bits):
        the_bytes = []
        byte = 0

        for i in range(0, len(bits)):
            byte = byte << 1
            if (bits[i]):
                byte = byte | 1
            else:
                byte = byte | 0
            if ((i + 1) % 8 == 0):
                the_bytes.append(byte)
                byte = 0
        #print(the_bytes)
        return the_bytes

    def __calculate_checksum(self, the_bytes):
        return the_bytes[0] + the_bytes[1] + the_bytes[2] + the_bytes[3] & 255

lora.py

# lora.py
import config
import utime
import time
from network import LoRa
import socket
import binascii
import struct
import machine


class LoraAU915: #Australia AU915
    # https://stackoverflow.com/questions/5690888/variable-scopes-in-python-classes
    lora = LoRa(mode=LoRa.LORAWAN, region=LoRa.AU915)

    def setupLora():
        #lora = LoRa(mode=LoRa.LORAWAN, region=LoRa.AU915)
        # Initialise LoRa in LORAWAN mode.

        # create an OTAA authentication parameters, change them to the provided credentials

        # whi-soil-3
        app_eui = binascii.unhexlify('your_device_app_eui')
        app_key = binascii.unhexlify('your_device_app_key')

        #Limit channels for AU915
        for i in range(0,8):
            LoraAU915.lora.remove_channel(i)
        for i in range(16,65):
            LoraAU915.lora.remove_channel(i)
        for i in range(66,72):
            LoraAU915.lora.remove_channel(i)

        # join a network using OTAA (Over the Air Activation)
        #uncomment below to use LoRaWAN application provided dev_eui
        #https://docs.pycom.io/tutorials/networks/lora/nvram/
        new_connection = True
        LoraAU915.lora.nvram_restore()

        if(LoraAU915.lora.has_joined() == False):
            print("LoRa memory restored but need to join LoRa")
            LoraAU915.lora.join(activation=LoRa.OTAA, auth=(app_eui, app_key), timeout=0)
        else:
            print("Memory restored and have rejoined LoRa with previous Dev Add")
            new_connection = False

        # wait until the module has joined the network
        while not LoraAU915.lora.has_joined():
            utime.sleep(1)
            if utime.time() > 15:
                print("possible timeout")
                machine.reset()
            pass

        print('Joined')
        # create a LoRa socket
        s = socket.socket(socket.AF_LORA, socket.SOCK_RAW)

        if new_connection:
            # set the LoRaWAN data rate
            s.setsockopt(socket.SOL_LORA, socket.SO_DR, 0)  # dr0 equiv to SF12

        # make the socket non-blocking
        s.setblocking(False)

        print("LoRa connection set up")
        utime.sleep_ms(5)
        return s

    def saveLora():
        LoraAU915.lora.nvram_save()
        print("LoRa setting saved to memory")

onewire.py

"""
OneWire library for MicroPython
"""

import time
import machine

class OneWire:
    CMD_SEARCHROM = const(0xf0)
    CMD_READROM = const(0x33)
    CMD_MATCHROM = const(0x55)
    CMD_SKIPROM = const(0xcc)

    def __init__(self, pin):
        self.pin = pin
        self.pin.init(pin.OPEN_DRAIN, pin.PULL_UP)

    def reset(self):
        """
        Perform the onewire reset function.
        Returns True if a device asserted a presence pulse, False otherwise.
        """
        sleep_us = time.sleep_us
        disable_irq = machine.disable_irq
        enable_irq = machine.enable_irq
        pin = self.pin

        pin(0)
        sleep_us(480)
        i = disable_irq()
        pin(1)
        sleep_us(60)
        status = not pin()
        enable_irq(i)
        sleep_us(420)
        return status

    def read_bit(self):
        sleep_us = time.sleep_us
        enable_irq = machine.enable_irq
        pin = self.pin

        pin(1) # half of the devices don't match CRC without this line
        i = machine.disable_irq()
        pin(0)
        sleep_us(1)
        pin(1)
        sleep_us(1)
        value = pin()
        enable_irq(i)
        sleep_us(40)
        return value

    def read_byte(self):
        value = 0
        for i in range(8):
            value |= self.read_bit() << i
        return value

    def read_bytes(self, count):
        buf = bytearray(count)
        for i in range(count):
            buf[i] = self.read_byte()
        return buf

    def write_bit(self, value):
        sleep_us = time.sleep_us
        pin = self.pin

        i = machine.disable_irq()
        pin(0)
        sleep_us(1)
        pin(value)
        sleep_us(60)
        pin(1)
        sleep_us(1)
        machine.enable_irq(i)

    def write_byte(self, value):
        for i in range(8):
            self.write_bit(value & 1)
            value >>= 1

    def write_bytes(self, buf):
        for b in buf:
            self.write_byte(b)

    def select_rom(self, rom):
        """
        Select a specific device to talk to. Pass in rom as a bytearray (8 bytes).
        """
        self.reset()
        self.write_byte(CMD_MATCHROM)
        self.write_bytes(rom)

    def crc8(self, data):
        """
        Compute CRC
        """
        crc = 0
        for i in range(len(data)):
            byte = data[i]
            for b in range(8):
                fb_bit = (crc ^ byte) & 0x01
                if fb_bit == 0x01:
                    crc = crc ^ 0x18
                crc = (crc >> 1) & 0x7f
                if fb_bit == 0x01:
                    crc = crc | 0x80
                byte = byte >> 1
        return crc

    def scan(self):
        """
        Return a list of ROMs for all attached devices.
        Each ROM is returned as a bytes object of 8 bytes.
        """
        devices = []
        diff = 65
        rom = False
        for i in range(0xff):
            rom, diff = self._search_rom(rom, diff)
            if rom:
                devices += [rom]
            if diff == 0:
                break
        return devices

    def _search_rom(self, l_rom, diff):
        if not self.reset():
            return None, 0
        self.write_byte(CMD_SEARCHROM)
        if not l_rom:
            l_rom = bytearray(8)
        rom = bytearray(8)
        next_diff = 0
        i = 64
        for byte in range(8):
            r_b = 0
            for bit in range(8):
                b = self.read_bit()
                if self.read_bit():
                    if b: # there are no devices or there is an error on the bus
                        return None, 0
                else:
                    if not b: # collision, two devices with different bit meaning
                        if diff > i or ((l_rom[byte] & (1 << bit)) and diff != i):
                            b = 1
                            next_diff = i
                self.write_bit(b)
                if b:
                    r_b |= 1 << bit
                i -= 1
            rom[byte] = r_b
        return rom, next_diff

class DS18X20(object):
    def __init__(self, onewire):
        self.ow = onewire
        self.roms = [rom for rom in self.ow.scan() if rom[0] == 0x10 or rom[0] == 0x28]
        self.fp = True
        try:
            1/1
        except TypeError:
            self.fp = False # floatingpoint not supported

    def isbusy(self):
        """
        Checks wether one of the DS18x20 devices on the bus is busy
        performing a temperature convertion
        """
        return not self.ow.read_bit()

    def start_conversion(self, rom=None):
        """
        Start the temp conversion on one DS18x20 device.
        Pass the 8-byte bytes object with the ROM of the specific device you want to read.
        If only one DS18x20 device is attached to the bus you may omit the rom parameter.
        """
        if (rom==None) and (len(self.roms)>0):
            rom=self.roms[0]
        if rom!=None:
            rom = rom or self.roms[0]
            ow = self.ow
            ow.reset()
            ow.select_rom(rom)
            ow.write_byte(0x44)  # Convert Temp

    def read_temp_async(self, rom=None):
        """
        Read the temperature of one DS18x20 device if the convertion is complete,
        otherwise return None.
        """
        if self.isbusy():
            return None
        if (rom==None) and (len(self.roms)>0):
            rom=self.roms[0]
        if rom==None:
            return None
        else:
            ow = self.ow
            ow.reset()
            ow.select_rom(rom)
            ow.write_byte(0xbe)  # Read scratch
            data = ow.read_bytes(9)
            return self.convert_temp(rom[0], data)

    def convert_temp(self, rom0, data):
        """
        Convert the raw temperature data into degrees celsius and return as a fixed point with 2 decimal places.
        """
        temp_lsb = data[0]
        temp_msb = data[1]
        if rom0 == 0x10:
            if temp_msb != 0:
                # convert negative number
                temp_read = temp_lsb >> 1 | 0x80  # truncate bit 0 by shifting, fill high bit with 1.
                temp_read = -((~temp_read + 1) & 0xff) # now convert from two's complement
            else:
                temp_read = temp_lsb >> 1  # truncate bit 0 by shifting
            count_remain = data[6]
            count_per_c = data[7]
            if self.fp:
                return temp_read - 25 + (count_per_c - count_remain) / count_per_c
            else:
                return 100 * temp_read - 25 + (count_per_c - count_remain) // count_per_c
        elif rom0 == 0x28:
            temp = None
            if self.fp:
                temp = (temp_msb << 8 | temp_lsb) / 16
            else:
                temp = (temp_msb << 8 | temp_lsb) * 100 // 16
            if (temp_msb & 0xf8) == 0xf8: # for negative temperature
                temp -= 0x1000
            return temp
        else:
            assert False

Arduino code for MKR Zero

• There are several different code segments used on the Pycom LoPy4 microcontroller to monitor temperature.
  • MKR_soil_1.ino - main Arduino program
  • chameleon.h - soil moisture sensor library (header file)
  • DS18B20.h - external temperature sensor library (header file)

MKR_soil_1.ino

/*
 * PROGRAM TO RECEIVE DATA FROM a chameleon soil moisture sensor (developed by CSIRO): 
 * https://viashop.csiro.au/chameleon-card-six-sensor-pack
 * And sent it online through LoRaWAN using a MKR 1300 board
 * Mind4Stormwater project: http://mind4stormwater.org, , feel free to use, reuse, modify, share!!
 * University of Melbourne / INSA Lyon
 * Frédéric Cherqui - fcherqui@gmail.com
 ----- last version 19/02/2020 ----

 Arduino MKR boards Serial pins 13(RX), 14(TX)
 * 
*/ 


float temperature; //soil temperature from the DS18B20
int temp_int = 0;
String temp_str = "0";

float resistance; // resistance measured (to be converted into soil moisture or water content)
int resist_int = 0;
String resist_str = "";


#include "chameleon.h"          //all functions related to soil moisture measure
#include "DS18B20.h"            //all functions related to temperature measure


void setup() {
  Serial.begin(9600); // initialize serial communications and wait for port to open
  Serial1.begin(9600);
  //Tempsensor.begin();    // Start up the Dallas temperature sensor
}


void loop() {
  resistance = medianValue();
  resist_int = int(resistance);
  resist_str = String(resist_int);
  
  //temperature = readTemp();
  //temp_int = int(temperature * 100);
  //temp_str = String(temp_int);

  // Send Serial message to Pycom LoPy
  Serial1.println(temp_str + "," + resist_str);

}

chameleon.h

const int sensorXAnalogPin = A2;
const int sensorYAnalogPin = A1;
const float knownResistor = 10.0;       // Constant value of known resistor in k Ohms

int nsamples = 20;                // take 20 samples to keep the median

#define stepwavedelayMicro       250   // microsecond: pulse width of Vcc uC applied to sensor, reading voltage at end of pulse

float ReadSensor() {
  int sensorVoltageX, sensorVoltageY;               // Measured sensor voltage from 0 to 1023
  float sensorVoltage;                              // Average of sensorVoltageX, sensorVoltageY
  
  //Forward current through sensor
  pinMode(sensorYAnalogPin, INPUT);                //Set the pin as drain
  pinMode(sensorXAnalogPin, OUTPUT);
  digitalWrite(sensorXAnalogPin, HIGH);             // set the voltage supply on
  sensorVoltageY = analogRead(sensorYAnalogPin);    // read the sensor voltage takes 125us
   Serial.println("sensorY "+String(sensorVoltageY));
  digitalWrite(sensorXAnalogPin, LOW);              // set the voltage supply off

  delayMicroseconds(stepwavedelayMicro); //small delay before reversing polarity (mandatory according to Matt!)

  //Reverse current through sensor
  pinMode(sensorXAnalogPin, INPUT);                 //Set the pin as drain
  pinMode(sensorYAnalogPin, OUTPUT);
  digitalWrite(sensorYAnalogPin, HIGH);             // set the voltage supply on
  sensorVoltageX = analogRead(sensorXAnalogPin);    // read the sensor voltage takes 125us
  Serial.println("sensorX "+String(sensorVoltageX));
  digitalWrite(sensorYAnalogPin, LOW);              // set the voltage supply off
  sensorVoltage = (sensorVoltageY + sensorVoltageX) / 2;

  delayMicroseconds(stepwavedelayMicro); //small delay before reversing polarity (mandatory according to Matt!)

  //Calculate resistance 
  float value= float(knownResistor) * ( 1023 - sensorVoltage ) / sensorVoltage;
  value = value * 1000;
  if (value>32000.0) {
    value = 32000.00;
  }
  Serial.print("---resistance: "+String(value)+" kOhms\n");
  return value;
} 

#include <RunningMedian.h>
  
float medianValue() { //code to take the median value of n samples
  Serial.println("\n*** MEASURING ***");
  float value;
  //Create an instance of the RunningMedian class with the number of samples to use
  RunningMedian samples = RunningMedian(nsamples);
  for(int i= 0; i<nsamples; i++){
    value = ReadSensor();   //to measure the resistance
    samples.add(value);
    delay(500);
   }   
   //Return the median value
  float finalValue=samples.getMedian(); 
  Serial.println("*** MEDIAN VALUE ="+String(finalValue));
  return finalValue; 
}

DS18B20.h

/*
 * Dallas Scientific temperature sensor
 * DS18B20
 * code based on: https://create.arduino.cc/projecthub/TheGadgetBoy/ds18b20-digital-temperature-sensor-and-arduino-9cc806
 * !! You will need a pull-up resistor of about 5 to 10 KOhm between the 1-Wire data line and your 5V power.
 */

// First we include the libraries
#include <OneWire.h> //https://www.pjrc.com/teensy/td_libs_OneWire.html (Arduino --> Manage Libraries --> OneWire by Jim Studt... version 2.3.5)
#include <DallasTemperature.h> //https://github.com/milesburton/Arduino-Temperature-Control-Library (Arduino --> Manage Libraries --> DallasTemperature by Miles Burton... version 3.8.0

#define ONE_WIRE_BUS 3 // Data wire is plugged into pin 3 on the Arduino 
#define ONE_WIRE_POWER 1 // Power wire is plugged into pin 1 on the Arduino 

OneWire oneWire(ONE_WIRE_BUS); // Setup a oneWire instance to communicate with any OneWire devices, (not just Maxim/Dallas temperature ICs) 
DallasTemperature Tempsensor(&oneWire); // Pass our oneWire reference to Dallas Temperature. 

float readTemp() { 
 Serial.println("\n*** MEASURING TEMPERATURE ***");
 pinMode(ONE_WIRE_POWER, OUTPUT);
 digitalWrite(ONE_WIRE_POWER, HIGH);             // set the voltage supply on
 delay(1000);

 Tempsensor.requestTemperatures(); // Send the command to get temperature readings 
 Serial.print("---Temperature is: ");
 float temp=Tempsensor.getTempCByIndex(0); // Why "byIndex"? You can have more than one DS18B20 on the same bus. 0 refers to the first IC on the wire 
 Serial.println(temp);
 if (temp==-127.00) {
   Serial.println("error!");
   return 0;
 } else {
   Serial.println(temp);
   return temp;
 }
 digitalWrite(ONE_WIRE_POWER, LOW);              // set the voltage supply off
}

Trouble shooting

• Ensure that all sensors have pull-up resistors connected to data lines.
• Ensure that the Pololu 5V regulator has a pull-down resistor connected to the shutdown (SHDN) pin.
• Ensure that the Pololu 5V regulator is plugged in correctly.
• Ensure that batteries used to power the circuit are fully charged and are in good health. The LoPy will not function correctly if batteries cannot deliver sufficient current on start up.
• Ensure that the Electrolytic capacitor is installed with the correct polarity.
• Ensure that the Pycom LoPy4 is plugged in correctly (LED closest to 5V regulator)