Softreset init problem Tasmota 4.3.3 on Wemos D1 and DHT22

[EkkiBrue]

Tasmota v14.3.0 on Wemos D1 with a DHT22 (AM2302) connected to 5v and D4

Pinout: DHT22 (AM2302) — Wemos D1

+	 	—	 	1	 	—	 	5v
OUT	 	—	 	2	 	—	 	D4
-	 	—	 	3	 	—	 	G

I reported this in a resolved DHT22 thread - but it seems the topic there was already closed . So I have to bring this up again as a new bug as it´s not exactly correlating to the former problem:

After a softreset from inside Tasmota, the data immediately becomes invalid (null). Only unplugging and replugging the DATA-Cable will restart the "send data process" again.

After reset via resetbutton or unplugging the power cord, data is displayed correctly and seems to remain.

I made a short video to make clear what my actual problem is.

https://m1z.eu/tasmobug2
pw: tasmota_14.3.0

Hope it helps to make clear that the bug has to do something with the init-part of the reset-code of Tasmota...

[tsmoneta]

Does your version of the DHT22 have an onboard 10 Kohm resistor between VCC and the data pin? If not, you need to add one.

[EkkiBrue]

It´s this one: https://components101.com/sensors/dht22-pinout-specs-datasheet#:~:text=How%20to%20use%20DHT22%20Sensor

In the "howto section" linked they talk about a 5K pullup resistor between VDD and DATA on MCU side - ist that what you mean ?

I still wonder why a soft-reset differs so much on initialising the data connection compared to a hard reset. Is this a bug in the hardware (MCU or DHT?) or in tasmota software ? Other sensors don´t need any resistors to function. I just try to understand why this is.

[tsmoneta]

The pull-up resistor on a DHT22 sensor is used to maintain the data line at the Vcc level when the sensor is not actively sending data, ensuring proper communication with the microcontroller by defining a clear voltage state for the data signal to transition between high and low levels during data transmission; it's essentially a mechanism to keep the data line in a known state when not being actively driven by the sensor itself. Some versions include the resistor, some don't.

[EkkiBrue]

Hi @tsmoneta . Thank you for your detailed answer. I guess it´s not the problem as my platine based DHT22 seems to have the resistor onboard. Please look at this picture: My Modell is the one on the black PCB.

https://deepbluembedded.com/arduino-dht22-library-code-examples tutorial/#:~:text=How%20to%20connect%20DHT22%20to%20Arduino%3F

There are two versions of the DHT22 sensors in the market. The bare DHT22 sensor (on the right) has 4 pins, and the DHT22 sensor’s module (on the left) has 3 pins. No external pull-up resistor is needed with the data pin of the DHT22 sensor, unlike the DHT11 sensor.

I updated the link to the explaining video above as the old MKV link didn´t work with most browsers. Please watch for reference.

[crhass]

I think you are using GPIO2, try GPIO14

See. #3522

I can also confirm that I run bare DHT22 sensors without the external pull up resistor and they work fine.