I have a bot that reads data from a DHT22 sensor on my Raspberry Pi. When users ask for temperature or humidity values, the bot always returns the same numbers even though the actual conditions have changed. It seems like the sensor readings get stuck at the first measurement and never update. Can someone help me understand why this happens?
dht22 sensors get cranky when you read them too often. they need at least 2 seconds between readings or they’ll just spit back cached values. your functions are calling read_retry every time, but if requests come in too fast, you’re getting stale data. add a time.sleep(2) before each reading, or better yet - cache the values with timestamps so you’re not hammering the sensor.
Your problem is trying to cram sensor polling, message handling, and timing into one script. I deal with this stuff daily - you need separate automation for sensor scheduling and bot responses.
Set up a system that continuously reads your DHT22 on schedule (respecting those 2-second intervals) and stores values where your bot can grab them instantly. No more blocking calls or stale readings.
I’d use Latenode with two workflows. First one polls your sensor every 30 seconds and pushes data to a simple database or JSON endpoint. Second handles your Telegram bot and fetches the latest stored values when users ask.
Your sensor readings stay fresh, bot responds instantly, and you avoid timing conflicts. If your sensor goes offline, the bot can still respond with the last good reading instead of crashing.
Latenode makes this clean - trigger sensor workflow on schedule and bot workflow on webhooks. No more while loops or handler registration headaches.
Your Telegram bot is not updating sensor readings because the handle_message function is defined inside the while True loop. This causes the function to be re-registered repeatedly, each time capturing the initial sensor reading. Subsequent user requests then use this stale, initial data. The while True loop itself is also unnecessary in this context.
Understanding the “Why” (The Root Cause):
The telepot library’s message_loop function handles incoming messages asynchronously. However, by placing the handle_message definition within the while loop, you’re creating a situation where a new handle_message function is defined with each iteration, overriding the previous one. Each instance of handle_message “remembers” the sensor values obtained at the moment of its creation. Because these values are read only once initially, they never get updated. Removing the unnecessary while True loop and correctly registering the handler outside of it resolves this issue.
Step-by-Step Guide:
Refactor the Code Structure: Move the handle_message function definition outside the while True loop. This ensures that the message handler is registered only once, correctly.
Remove the Unnecessary Loop: Delete the while True loop entirely. The bot.message_loop(handle_message) function already runs indefinitely, waiting for and processing incoming messages.
Verify Sensor Readings: Ensure that your get_temperature() and get_humidity() functions correctly read the sensor values each time they are called. These functions should not cache values between calls. The Adafruit_DHT.read_retry() function should be called each time a user asks for temperature or humidity, to provide updated data. Consider adding error handling for cases where the sensor reading fails.
Here’s the corrected code:
import Adafruit_DHT
import telepot
TOKEN = 'YOUR_BOT_TOKEN'
bot = telepot.Bot(TOKEN)
sensor_type = Adafruit_DHT.DHT22
pin_number = 4
def get_temperature():
humidity_val, temp_val = Adafruit_DHT.read_retry(sensor_type, pin_number)
if temp_val is not None:
return temp_val
else:
return "Sensor reading failed" # Handle sensor read errors gracefully
def get_humidity():
humidity_val, temp_val = Adafruit_DHT.read_retry(sensor_type, pin_number)
if humidity_val is not None:
return humidity_val
else:
return "Sensor reading failed"
def handle_message(msg):
chat_id = msg['chat']['id']
command = msg['text']
if command == '/start':
bot.sendMessage(chat_id, 'Hello! Ask for temperature or humidity')
elif command.lower() == 'temperature':
bot.sendMessage(chat_id, f'Current temp: {get_temperature()}')
elif command.lower() == 'humidity':
bot.sendMessage(chat_id, f'Current humidity: {get_humidity()}')
bot.message_loop(handle_message)
Test Thoroughly: After making these changes, thoroughly test your bot to ensure that it correctly retrieves and displays updated sensor readings with each request.
Common Pitfalls & What to Check Next:
Sensor Frequency: DHT22 sensors require a minimum delay between readings (around 2 seconds). If you’re reading too frequently, you might still get stale data. Add a short delay (time.sleep(2)) between calls to Adafruit_DHT.read_retry() within your get_temperature() and get_humidity() functions if necessary.
Sensor Wiring: Double-check your DHT22 sensor wiring to the Raspberry Pi. Incorrect wiring can prevent proper readings.
Libraries: Make sure you have the correct Adafruit_DHT library installed and configured.
Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!
Your code’s got a structural problem. You’re reading sensor values once in the while loop, then defining the handler function inside that same loop. This creates multiple handlers and captures those initial readings - they never refresh because the handler functions lock onto those first values. Pull the handler function out of the while loop and ditch that initial sensor reading. Your get_temperature() and get_humidity() functions already call Adafruit_DHT.read_retry(), so they’ll grab fresh readings when users request them. You probably don’t even need the while True loop - just call bot.message_loop() once after defining your handler. That way each user request triggers a new sensor reading instead of using stale data.
Understanding the “Why” (The Root Cause):
Step-by-Step Guide:
Common Pitfalls & What to Check Next:
Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!