DHT22 AM2302 sensor doesn't work in nodered

General
1

Platform: pi 3 model B+ rev.1.3

OS: Rasbian

Node-RED: 1.0.5

Node.js: v12.17.0

problem node: node-red-contrib-dht-sensor v1.0.4

bcm2385 revision. a020d3

DHT22 sensor: AM2302

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Hello I'm new in using Nodered but I found it perfect for my home automation project.

I bought 2 sensors DHT22 instead of the DHT11.

I used succesfully the DHT11 sensor connected to GPIO23 (physical pin 16) recieveing temperature and humidity values.

I changed the DHT11 with the DHT22 sensor connected to the same GPIO23 and changing the sensor model into the node-red-contrib to DHT22

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and I recived wrong values as output:

{"_msgid":"99d420d7.3025b","topic":"rpi-dht22","payload":"0.00","humidity":"0.00","isValid":false,"errors":4,"location":"Test_T&H","sensorid":"dht22"}

I tried the same sensor with the same connection with Adafruit library and it works properly

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I don't know how to solve it. But for me it's necessary to find a solution because I want to continue to work with nodered.

Can someone help me?

Thank you

Regards

2

I had the same thing happen when I switched from a dht11 to dht22. What finally fixed mine was changing the pin numbering from physical pins to bcm. Sounds dumb but it worked.

3

Thanks gerry for your suggestion but in my case it doesn't work. I changed from Physical pins (rev.2) to
BCM gpio

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following my wiring connection

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but I always received wrong values:

{"_msgid":"e68c589b.d4d8f8","topic":"rpi-dht22_test","payload":"0.00","humidity":"0.00","isValid":false,"errors":4,"location":"Test_T&H","sensorid":"dht22"}

I tried also to change the connection pin to other pins but nothing happened.

I thought the possible problem could be the correlation between the pins in the list node-red-contrib-dht-sensor and the real pins so I changed (and tested) all the proposed pin numbers into the node-red-contrib-dht-sensor list, but nothing.
Following my wiring pin table:
image

Could the problem be a no compatibility of the sensor DHT22 AM2302 with the node-red-contrib-dht-sensor? Or does it depend from my hardware configuration?
Does anyone know if there is an alternative palette to node-red-contrib-dht-sensor to control a DHT22 sensor into nodered?

4

Just to verify, did you install the BCM2835 library and node-dht-sensor as it says in the pre-req's?

5

No I didn't install the BMC libraries as told in the pre-req's.

But I just do it and update the BMC to the version 1.65:
image
Then I followed the other 2 steps in pre-req's and I re-installed the node-dht-sensor dependency and the node-red-contrib-dht-sensor node.
And I updated npm to the latest version (patch) 6.14.5 and Node-js to version 12.17.0

The output values coming from node-red-contrib-dht-sensor are still wrong with both BCM GPIO (in my case 23) or Physical pin rev.2 (in my case 16).

6

Are you sure you have the pins connected properly? Is it possible the dht22 pin outs on the board are different than the dht11?

7

After installing the BMC v1.65 library, node-dth-sensor and then the node-red-contrib-dht-sensor, I wired up a dht22 using:
Pin 1 (3.3v) to pin 1 of the dht22
Pin 6 (Gnd) to pin 4 of the dht22
Pin 16 (BCM 23) to pin 2 of the dht22
and a 10K resistor between pins 1 and 2 of the dht22

the node is reporting fine.

{"_msgid":"591e2642.bdc308",
  "topic":"rpi-dht22",
  "payload":"23.20",
  "humidity":"34.60",
  "isValid":true,"errors":1,
"sensorid":"dht22"}

I would uninstall/install node-red-contrib-dht-sensor and try again. If that doesn't work, try another dht22.

8

Just a note: Be careful with the resistor as many of the packaged DHT sensors have the resistor already in the circuit. I don't know if the DHT you are using has one or not but read the data sheet carefully.

9

Hello I bought and tested a new sensor DHT22 (a branded one) and now it works fine. So my problem was the sensor.
I suggest to buy brended sensors and not generic unbrended sensors and of course to use the good node-red-contrib-dht-sensor.
Thanks to gerry and zenofmud for your suggestions

10

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