is there a way for python to check for value change and then trigger a function?

Question

I am doing a school project that is using a raspberry pi model 3b and dht11 to measure the temperature. I want the temperature data to be sent to a cloud service(Beebotte) only when the value of the temperature is increasing or decreasing. Do I need to use the observer pattern for this? Below is the code for my school project:

import pygame
import Adafruit_DHT #Import DHT Library for sensor
import time
import datetime
from time import sleep, strftime
import Adafruit_CharLCD as LCD
import requests
from beebotte import *

_accesskey  = 'My accesskey'
_secretkey  = 'My secretkey'
bbt = BBT( _accesskey, _secretkey)

GPIO.setwarnings(False)

lcd_rs = 27
lcd_en = 22
lcd_d4 = 25
lcd_d5 = 24
lcd_d6 = 23
lcd_d7 = 18
lcd_backlight = 4

lcd_columns = 16
lcd_rows = 2

lcd = LCD.Adafruit_CharLCD(lcd_rs, lcd_en, lcd_d4, lcd_d5, lcd_d6, lcd_d7, lcd_columns, lcd_rows, lcd_backlight)

ReedSwitchPin = 17
LED = 21

sensor_name = Adafruit_DHT.DHT11 #we are using the DHT11 sensor
sensor_pin = 16 #The sensor is connected to GPIO16 on Pi

RawValue = 0

timer = time.time()

#buzzer = 5

#Setup
GPIO.setmode(GPIO.BCM)
GPIO.setup(ReedSwitchPin, GPIO.IN)
GPIO.setup(LED, GPIO.OUT)
#GPIO.setup(buzzer,GPIO.OUT)
#SFX
pygame.init()
pygame.mixer.init()
Alarm = pygame.mixer.Sound("/home/pi/python_games/bomb.wav")

try:
    while True:
        RawValue = GPIO.input(ReedSwitchPin)

        if (RawValue == 0):
            lcd.clear() #Clear the LCD screen
            GPIO.output(LED,True)
            if time.time() - timer > 30:
                def telegram_bot_sendtext(bot_message):
                    bot_token = 'my bot_token' #token that can be generated talking with @BotFather on telegram
                    bot_chatID = 'my bot_chatID'
                    send_text = 'https://api.telegram.org/bot' + bot_token + '/sendMessage?chat_id=' + bot_chatID + '&parse_mode=Markdown&text=' + bot_message

                    response = requests.get(send_text)

                    return response.json()
                    GPIO.output(LED,True)
                    Alarm.play()
                test = telegram_bot_sendtext("The refrigerator door is left open! Please close it immediately") # the message to send 

        else:
            GPIO.output(LED, False)
            Alarm.stop()
            humidity, temperature = Adafruit_DHT.read_retry(sensor_name, sensor_pin) #read from sensor & save respective values in temperature and humidity variable
            lcd.clear() #Clear the LCD screen
            lcd.message ('Temp = %.1f C' % temperature) # Display the value of temperature
            previous_temperature = None

            while True:
                if temperature != previous_temperature:
                    bbt.write("MonitoringTemperature", "Temperature", temperature)
                previous_temperature = temperature
                break

        # 0 is off, 1 is activated by magnet
        #print(" ,RawValue:",RawValue)

        time.sleep(1)

except KeyboardInterrupt:
    pass
print("Exiting Reed Switch Test ...")

GPIO.cleanup()

You just need to keep track of the previous few readings, and probably do some smoothing to cope with ambient variations. — tripleee, Feb 07 '20 at 13:19
Totally unrelated but you want to move your `telegram_bot_sendtext` function definition out of the main loop - there's no need to redefine the same function over and over and over again. Also, the two lines after the `return reponse.json()` will never be executed. — bruno desthuilliers, Feb 11 '20 at 15:27

Phoenixo · Accepted Answer · 2020-02-11T15:17:37.220

You could use a previous_temperaturevariable to check if the value changed :

previous_temperature = None

while True:
    temperature = input("Give me the new temperature :")
    if temperature != previous_temperature:
        print("trigger something !")
    previous_temperature = temperature

** EDIT **

In my example I used input() to simulate your new temperature, but in your case you use humidity, temperature = Adafruit_DHT.read_retry(...). So you have to put this code inside the while loop. I also added a time.sleep() so the system waits 10 seconds before reading the new temperature value.

Try this :

        else:
            GPIO.output(LED, False)
            Alarm.stop()
            lcd.clear() #Clear the LCD screen
            previous_temperature = None

            while True:
                humidity, temperature = Adafruit_DHT.read_retry(sensor_name, sensor_pin) #read from sensor & save respective values in temperature and humidity variable
                lcd.message ('Temp = %.1f C' % temperature) # Display the value of temperature
                if temperature != previous_temperature:
                    bbt.write("MonitoringTemperature", "Temperature", temperature)
                    break
                previous_temperature = temperature
                time.sleep(10) # wait 10 seconds before reading the new temperature

Thanks for the reply! Do I need to use temperature = input("Give me the new temperature :") since my temperature variable is = the data read from the sensor. And how do you exit the while True loop? Sorry for the late reply! — Loon, Feb 11 '20 at 11:23
Forget about the last question I asked! I found out the answer, it's the break statement. But when I use the previous_temperature variable and checked my dashboard, it still sends the data even though the temperature is the same. Anyways, I'm already running a while True loop which I didn't include in this question. If I were to run 2 while True loop, will it affect anything? — Loon, Feb 11 '20 at 11:52
I have updated the codes. Please have a look! Thank you very much — Loon, Feb 11 '20 at 11:55

is there a way for python to check for value change and then trigger a function?

1 Answers1