Temperature sensor

Authors

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

Applications

Temperature is one of the easiest sensor projects to start with. Applications include:

• Monitoring the temperature of a smart bee hive, rabbit hutch, chick coop, compost heap, worm farm, aquarium or wetland.
• Experimenting with concepts related to energy efficient building construction.
• Temperature compensation for other sensors (sensor values may change with changes in temperature).
• Making a weather station.

Key design considerations

• Circuit was originally powered with a 0.5W solar panel (0.5W Solar Panel 55x70 (Core Electronics) SKU: SS313070004). This was removed because the deep sleep function on the LoPy4 is very efficient. Removing the solar panel also keeps the circuit more simple.
• An external antenna (Pycom LoRa & Sigfox Antenna Kit (Core Electronics) SKU: CE04928) was originally used to improve signal strength. This was replaced with a more compact Molex flat antenna that could be mounted within the sensor housing.
• An electrolytic capacitor was added to the input of the Pololu voltage regulator to help prevent voltage spikes.
• Pull-up and pull-down resistors were added to the data lines on the temperature sensors and the voltage regulator.
• 5V regulated supplies are used by both temperature sensors, although these sensors can run on 3.3V.
• The 5V regulator supply is turned on and off using a shutdown pin (SHDN) and this also cuts the power supply to both temperature sensors.
• High precision 10k ohm resistors (<0.1% variation) were used for the voltage divider circuit.
• LoPy4 RGB LED used to signal program status. RGB LED can be commented out of program to reduce power consumption.

Types of temperature sensors

The are two common temperature sensors that are used in this sensor.

• An internal temperature and humidity sensor is the DHT22. This is included in all sensor project to monitor temperature and humidity conditions within the sensor housing. If the temperature gets too hot or too cold within the sensor housing this may shorten the life of the equipment and the batteries.
• An external temperatures sensor is the DS18B20. External sensors are typically water proof and have a longer cable. They can be used to monitor a range of interesting discovery learning projects.

DHT22 Internal temperature sensor

Overview

• The DHT22 temperature and humidity sensor that is placed within the sensor housing.
• Normally this sensor is used to detect abnormally high or low temperatures, or excess humidity.
• Extreme conditions can reduce the functional life of the sensor.
• The following link is a good reference to the use of the sensor. [[1]]

Important notes

• DHT22 Pin layout
  • Pin 1 is VCC (Power Supply)
  • Pin 2 is DATA (The data signal)
  • Pin 3 is NULL (Do not connect)
  • Pin 4 is GND (Ground)
• The DHT22 is a slow sensor which requires up to 2 seconds to take a reading
• It can operate at 3.3V or 5V, but 5V is preferable.
• The DHT22 requires a 10K pull-up resistor between pins 1 (VCC) and 2 (DATA). Failure to do this will result in data loss.

DS18B20 External temperature sensor

• The DS18B20 temperature sensor is waterproof and can be used for most external temperature sensing functions.
• It uses the one-wire library for communication.
• It can be powered using 3.3V or 5V supplies.
• For correct operation it requires a 10k ohm pull-up resistor connected between VCC and DATA pins.

Software installation requirements

• Atom installed on PC or Mac with Pymakr package installed

Parts list

Item description	Number	Supplier	Part number	URL	Cost	Notes
Solder-able Breadboard	1	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
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
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	2	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 board.

• Close up of board.

• Close up of board without LoPy4.

• Close up of board from DHT22 temperature sensor end.

• Close up aerial view of board without LoPy4.

Electronic circuit construction

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 I10
• GND from negative rail nearest to J to pin J11

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 E21
• VCC connection from E30 to H4

Pololu 5V Step-Up Voltage Regulator U1V11F5

• Cut female header pins to 4 pin length
• Solder from pins F1 to F4
• Solder right angle male header pins to Regulator so board stands upright (supplied with regulator)
  • F1 to shutdown (SHDN)
  • F2 to input voltage (VIN) - from battery
  • F3 to ground (GND)
  • F4 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 G2
• Electrolytic Decoupling Capacitor negative terminal G3
• VIN (3.3V from LoPy4) from J12 to J2
• SHDN (shutdown) pin connected from pin E20 to H1

DS18B20 external temperature sensor

• Cut female header pins to 3 pin length
• Solder from pins A1 to A3
  • A1 to DATA
  • A2 to VCC
  • A3 to GND
• Solder right angle male header pins to temperature sensor leads
• GND connection from pin B3 to B27
• DATA connection from pin D1 to D23
• VCC (5V regulated supply) connection from pin E2 to I4
• 10k ohm pull-up resistor (low precision) from pin B1 to B2

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

import binascii #module that makes conversion between binary and Ascii
import config
from dth import DTH
import gc # garbage collection
from lora import LoraAU915
import machine
from machine import Pin
from machine import ADC
from onewire import DS18X20
from onewire import OneWire
import pycom
import network
import socket
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 all sensors
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()

####################################
### LOOP IF NO NEED TO SLEEP #######
####################################

while True:
    sensor_power.value(1)  # power up
    time.sleep(1)
    pycom.rgbled(config.ORANGE)
    time.sleep(1)
    pycom.rgbled(config.OFF)


    # TEMPERATURE AND HUMIDITY OF AMBIENT AIR
    j=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")
            break
        time.sleep(1)
        j += 1
        print("Error code %d" % result.error_code)
        print(j)
    print("Temperature = = %.2f C" % result.temperature)
    print("Humidity = %.2f %%" % result.humidity)
    print("Error code final %d" % result.error_code)

    # 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)

    #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/

    ow = OneWire(Pin(config.DS18B20_DATA))
    temp = DS18X20(ow)

    soil_temp = 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_temp_t = int(soil_temp*100)
    print(soil_temp_t)
    batt_volt_t = int(batt_volt*100)
    print(batt_volt_t)
    sens_temp = int(result.temperature*100)
    print(sens_temp)
    sens_humi = int(result.humidity*100)
    print(sens_humi)

    # converting 2 byte values into single bytes for transmission
    soil1 = int(soil_temp_t//256)
    soil2 = 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,batt1,batt2,temp1,temp2,humi1,humi2)
    s.send(bytes([soil1,soil2,batt1,batt2,temp1,temp2,humi1,humi2]))
    s.setblocking(False)

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

    # note that batt_volt has been multiplied by 100 for transmission
    if (batt_volt > 4.0):
        # 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.py
########################

# 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
DS18B20_DATA = 'P12' # pin that receives data from external temp 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-seedling-1
        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

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)