Enhancement Request: DHT22 (DHT11 DHT2302)

[AnonymousMonkeyNo12]

I would like to use the DHT22 Thermometer and Hygrometer sensor.

It implements it's own one-wire (1 wire) protocol.

I got it working on my rpi4 using this guide

Which downloads the following repo and runs the pi code.

https://github.com/adafruit/Adafruit_Python_DHT

Now I would like to use this sensor with diozero, since I am already controlling multiple other devices through it.

If there is currently no possibility for somebody else to implement it, I am willing to attempt to implement it myself (I have never worked with low level stuff, C or JNI before), but any pointers would be very welcome, especially in regards to:

• How to deal with the c files
• How to deal with different raspberry pi versions? (There are different c files depending on the device)
• Is there already some build in stuff I can use ( I have found the one wire stuff, but it seems to be some kind of standard, contrary to the DHT22 custom protocol)

Thanks in advance and cheers.

[EAGrahamJr]

Just a couple of suggestions:

1. you shouldn't have to deal with the .c files or JNI or anything like that: diozero already handles that stuff
2. the Adafruit link is to a deprecated driver
3. the newer driver would be a better reference
4. I'm not sure what you'd use for the Pulsio library, so Matt might have a better notion on that
5. I'd also check in the available devices for something that looks like what you've got -- that's also usually a good reference.

[AnonymousMonkeyNo12]

@EAGrahamJr Thank you for your input.

I was thinking I can just drop in the C driver files here and write a simple wrapper to call them, but you are suggesting re-implementing it from scratch directly in diozero by using it's existing functions, did I understand that correctly?

(That is also why I looked into the older driver. It is pretty easy to just drop the c files, make install them and use the resulting .so compared to whatever the new stuff is doing, which seems to be distributed across multiple dependencies.)

Is java/diozero fast enough for the custom 1 wire protocol of the DHT22? I tried to test my understanding of the protocol by writing a quick and dirty bash script, but it was too slow to detect the edges in the signal.

I looked at the existing 1 wire stuff, but it seems to me like it is meant for the standard only. Do you have any more clues on how I would declare a custom protocol (How to tell the software to set the wire to low and start listening for a specific "header" followed by the data of a certain length)?

---

For reference:

There is also this micropython library:
https://github.com/danjperron/PicoDHT22/blob/main/PicoDHT22.py

[AnonymousMonkeyNo12]

I have noticed that there is the Firmata protocol in diozero which seems to already support the dht sensors https://github.com/firmata/protocol/blob/master/dhtsensor.md

[mattjlewis]

Apologies for being away - AI Masters + work... Yes - Firmata is a good choice, I've put a lot of effort into getting that working.