DHTT22 zero values

General
1

Have been using node-red-contrib-dht-sensor with DHT22 sensor showing zero values in temperature and humidity :
(object
_msgid: "2bea0790.4d4168"
topic: "rpi-dht22"
payload: "0.00"
humidity: "0.00"
isValid: false
errors: 4
sensorid: "dht22" }.

Anyone has any idea what went wrong? I'm using the Physical Pin Rev.2 with pin 15. All other grounded + power(3.3) are placed correctly. Much Appreciated

2

Not sure about the node since I've never used it. However, I have used DHT22's in the past - they are not much better than the DHT11's and will occasionally give back a rubbish answer. As the isValid flag is false, that suggests that the result was rubbish but that the node author decided to make the values zero in such a case - not a good choice in my opinion, they should be something obviously wrong like -99 or, even better, null.

By the way, the DHT 11/22 are rubbish because they are not only terribly inaccurate to begin with but also the sensor drifts over time.

I recently was putting together another sensor platform for the house and decided to put a DHT22 amd a SI7021/HTU21D on the same platform (ESP8266 based), here are the current readings (the DHT22 is the top reading):

image

As you can see, there is a very significant difference between them. When I tested this platform along-side some of my existing ones just to make sure that I didn't have a duff sensor, the SI7021 gave readings consistent with the other sensors which were either other SI7021's or BME280's.

3

Wow! Thanks for the feedback! I would give SI7021 a try. Incidentally DHT22 was working fine until a damage to the sensor due to incorrect power. After that I tried to use a new DHT22 but these zero errors started appearing. I checked the Pins on the Pi and are fine.