Pressure sensor

Pressure sensor

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

How to use a pressure sensor

The

DHT22 Internal temperature sensor

Overview

• The DHT22 t

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)

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.

• Side view of board without LoPy4

• 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 J10
• 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 D21 - different from temperature sensor
• VCC connection from E30 to G4 - different from temperature sensor

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 I3 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

Atlas Pressure Transducer A-10 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 C3 to B27
• DATA connection from pin C1 to F17 - analog input on LoPy4
• VCC (5V regulated supply) connection from pin E2 to F4

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')

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
}

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")

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)