Problem: wrong values at negative temperatures an ESP8266 and DHT22

[argltuc]

• Arduino board: ESP8266 / NodeMCU 1.0 (ESP12-E Module)
• Arduino IDE version (found in Arduino -> About Arduino menu): 1.8.13
• installed DHT-sensor-library version: 1.4.1 / installed by Arduino IDE Lib manager

I use the DHT22 in combination with an ESP8266 and this lib.
When having negative temperatures, the resulting value of readTemperature() is -3278.6 at -0.1°C
To fix negatives values a recalculation is nessecary:

#include <stdint.h>
float temperature = dht.readTemperature();
if(temperature < 0)
 {
   temperature = (temperature = (INT16_MAX - temperature*-10)*-0.1; - temperature*-10)*-0.1;
 }

after some research, i figure out, that the values in data-array repressents an intager in ones complement, while the rest of data handling seems to be in BCD.
I will provide an PR to fix this issue.

[Maaajaaa]

I tried to repeat the bug with an ESP32 but all negative celsius temperatures that I got (though I did not get -0.1 in particular) seemed correct to me. Does this only concern -0.1C in partocular?

• Arduino board: ESP32-CAM
• Arduino IDE 1.8.12
• installed DHT-sensor-library version: 1.4.2

[argltuc]

If i remember correctly all negative values were wrong. Less temperature results in respective higher value then -3278.6.
Currently i can't repeat my measurements, since all my DHT22 sensor are used and fully integrated in some projects.

[tranquil-c]

I have been seeing this issue and have yet to narrow down on the cause.

I'm using version 1.4.4 of this library and building with PlatformIO:

• framework-arduinoespressif32 @ 3.20007.0 (2.0.7)
• tool-esptoolpy @ 1.40500.0 (4.5.0)
• toolchain-xtensa-esp32 @ 8.4.0+2021r2-patch5

I've observed it twice now. On both occasions the temperature decreased, crossing 0 degrees, over the course of roughly an hour.

I'll be investigating the issue and will provide an update should I find anything notable.

[naymore]

I know this thread is quite a bit old but I couldn't find any real solution to the problem.
I'm using v1.4.6 of this library (on an ESP8266) and I can confirm the problem is real.