Good Sensor, strange protocol.

The DHT22 explicitly advertised with its suitability for the Raspberry Pi, but this turns out that he is not so great together playing with Pi. This is due to the signaling protocol on the data line, which is compatible with anything that the Pi brings from home. Even after a long search on the net I have found only one device driver for these did not try because of some obvious defects and bugs. But as I just wanted to take into operation the sensor without starting before a large software project for me so I have operated one of the many user-mode polling variants. I am an experienced embedded software developers that do for a living for a long time. Therefore, I can only say: a grisly solution!

The Pi needs before two - three attempts, until he finds out a proper measurement of the sensor. However, he gets through the checksum mitschickt the sensor fortunately, mostly with whether the metrics are broken.

The sensor itself has been proven so far, however. The measured temperatures are consistent with those of a Vergleichstermometers, the moisture values ​​are plausible in any case. Also, the sensor with the 3.3V operating voltage of Pi is still cope, which is also indicated in the data sheet minimum voltage. With 5V you should not operate it at Pi rather, since the voltage on the signal line is then a bit too high.

In most wirings one sees the sensor with a 4,7kOhm pull-up on the data line. This can save with appropriate software actually because the GPIO ports of Pi can be configured to pull-up internally.

Conclusion: Good sensor adjusts very well to microcontrollers (Arduino), but rather a compromise solution for Raspberry Pi value is excellent.!