Timeline for Incorrect reading from DHT22 (on a Nano board)
Current License: CC BY-SA 4.0
8 events
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| Oct 25, 2023 at 19:39 | comment | added | nick | Thanks @st2000 for the further input. As for the additional 10k resistor: The IDUINO version of the DHT22 comes with this little break out board which I assume takes care of that. Like in the schematic here from makerguides.com, such one is not necessary. I am going to try to supply this sensor with a different voltage on the weekend and check out your suggested links. Still I guess it is just broken. | |
| Oct 17, 2023 at 12:38 | comment | added | st2000 | I added some links to some forum discussions about the DHT22 humidity sensor. There are more good suggestions in some of these if you want to go the distance. But I'd check the voltage at the sensors, I might try the pull up (but I think there's only a slim chance that will work) finally I would switch to some of the recommended sensors and buy from a well established company that has a community of uses who you can ask questions of. | |
| Oct 17, 2023 at 12:34 | history | edited | st2000 | CC BY-SA 4.0 |
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| Oct 17, 2023 at 12:24 | comment | added | st2000 | Oh! Something you might try. You didn't provide a schematic. But if the internet is anything to go by, about 33% of DHT22 projects posted place a 10K pull up resistor on the DHT22's data pin. This is because most serial interfaces like this one use a open collector output so that multiple devices can share a single digital wire. What about the other 77%? Well, the driver should activate an internal processor pull up resistor. But, these resistors very widely. So, try adding a 10K pull up resistor the the digital pin of the problematic DHT22 ... just to see what happens. | |
| Oct 17, 2023 at 12:13 | comment | added | st2000 | I meant to check the voltage provided the DHT22 sensors. Some Arduinos run at 3.3V and others at 5V. Somewhere I read the DHT22 runs better at the higher voltage. I see the Alexnd webpage says 5V and the Grove web page says 3.3 to 5V. LOL. Also, you may have a bad sensor. Do you have another to swap out with? Lastly, I've had bad luck w/DHT22 sensors too and switch to Sillicon Lab Si7021 sensors. | |
| Oct 17, 2023 at 8:30 | comment | added | nick | The specifications for this sensor in the link above states that it reports RH. This leaves the programming. Not sure if I am able to go into the DHT.h. I assume the problem is still with the sensor. Coming back to my initial question: is it possible to redo the calibration on that one? | |
| Oct 17, 2023 at 8:24 | comment | added | nick | Thank you so much @st2000 for this detailed answer and the good hints on how to proceed! What I checked: The voltage on the USB to the Nano is 5.06V with 0.023A (no difference if one or both sensors are connected). I tried an USB hub with additional power, no effect. I set the delay(10000), which doubled the time but had no effect. I put the whole setup into a plastic container. After 30 minutes of equilibration the humidity readings are keeping this difference. The temperature however is now 0.1° apart :) . You clearly ruled out that the sensor is reporting AH instead of RH. | |
| Oct 14, 2023 at 14:49 | history | answered | st2000 | CC BY-SA 4.0 |
