CODEWITHSUNDEEP
pythonflaskraspberry-pihardware
SeongMin Park
SeongMin Park

Reputation: 75

RPI dht22 with flask: Unable to set line 4 to input - Timed out waiting for PulseIn message

I'm trying to make a Raspberry Pi 3 REST API that provides temperature and humidity with DHT22. The whole code:

from flask import Flask, jsonify, request
from sds011 import SDS011
from adafruit_dht import DHT22
import board
import os
import time

app = Flask(__name__)
dht = DHT22(board.D4)

def get_dht_data():
    while True:
        try:
            temperature, humidity = dht.temperature, dht.humidity
            print(temperature, humidity)
            if temperature is not None and humidity is not None:
                return temperature, humidity
            else:
                raise
        except:
            time.sleep(0.5)

@app.route('/', methods=['GET'])
def status():
    temperature, humidity = get_dht_data()

    return jsonify({
        'temperature': temperature,
        'humidity': humidity
    })

if __name__ == '__main__':
    app.run(debug=True)

I used https://github.com/adafruit/Adafruit_CircuitPython_DHT

However, when I start server, it shows message

'Unable to set line 4 to input'

and temperature and humidity is always None. If I don't run flask app but just DHT code, it works.

Upvotes: 3

Views: 4676

Answers (5)

Infineight
Infineight

Reputation: 568

Disabling 1-wire in the rasbian config resolved the issue for me.

sudo raspi-config

Select 3 Interface Options, then I7 1-Wire and disable it by selecting No and rebooting the device.

Upvotes: 0

THEMISTOKLIS ANASTASOPOULOS
THEMISTOKLIS ANASTASOPOULOS

Reputation: 1

I am facing the same issue with you meaning that using python, flask and cyrcuitpython adafruit_sht library I can only run once for every pin on rpi 4 the code. Finally the solution was in front of me and was the line dhtDevice.exit()

So before ending my code and return to the main class I run the command dhtDevice.exit() so the next time I run the same code evrything works fine!

Upvotes: 0

sirpask
sirpask

Reputation: 1

Blockquote In my case, pgrep libgpiod_pulsein returned nothing. But changing pin to D18 solved the issue. Seems to me like something else is blocking GPIO4, but no idea what. – Slav Apr 4 at 18:03

thanks,with the pin 18 its ok

but it is strange:

The pin 4, only run it: (version deprecated of adafruit)> runing before:

sudo modprobe w1-gpio

sudo modprobe w1-therm

#!/usr/bin/python
import sys
import Adafruit_DHT

while True:

    humidity, temperature = Adafruit_DHT.read_retry(11, 4)
    print 'Temp: {0:0.1f} C Humidity: {1:0.1f} %'.format(temperature, humidity)

Upvotes: 0

jsubirat
jsubirat

Reputation: 46

Short answer

Remove debug=True and enjoy. :-)

What was going on?

This problem drove me nuts but I think I found the root cause! In my case, I was encapsulating the DHT22 object in another object, like so:

...
class DHT22Custom:
    def __init__(self):
        print("**** BUILDING by {0}!".format(threading.currentThread().getName()))
        self.dht_device = adafruit_dht.DHT22(board.D17)
...

My main.py looked like:

import RPi.GPIO as GPIO
from sensor.config.app_config import create_app

if __name__ == '__main__':
    app = create_app()         # builds DHT22Custom inside
    app.run(debug=True)
    print("Cleaning up GPIO before exiting...")
    GPIO.cleanup()

And look what an interesting output I got:

root@05600e5:/app# python -m sensor.main
**** BUILDING by MainThread!
 * Serving Flask app "FlaskWS" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
**** BUILDING by MainThread!
Unable to set line 17 to input

The MainThread was initializing my object twice! How was that? Well, if you look at the documentation of Flask's run(), you'll see the following:

If the :attr:`debug` flag is set the server will automatically reload
 for code changes and show a debugger in case an exception happened.

So, it seems that Flask just relaunches the application or something like this. Not clear to me, to be honest. But well, if you just remove debug, you'll see something like:

root@05600e5:/app# python -m sensor.main
**** BUILDING by MainThread!
 * Serving Flask app "FlaskWS" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

I hope this helps. Happy coding!

Upvotes: 3

Brien Foss
Brien Foss

Reputation: 3367

Locating the process libgpiod_pulsein and killing it resolved the issue.

In your terminal, search for the process ID:

pgrep libgpiod_pulsein

and

kill <PID> (found from above - you might have more than one running)

I was experiencing the exact same thing with the DHT11. In my situation I had to kill the process: libgpiod_pulsein.

Worked on the first try when on fresh boot, but then subsequent executions would fail. Changing the GPIO I was using and running the program had the same effect, worked the first time and subsequent attempts would fail with example:

Unable to set line 4 to input

Timed out waiting for PulseIn message

Timed out waiting for PulseIn message ...

Upvotes: 0

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