The Python libraries provided by hobby supply vendors are probably fine for this sensor. I scrounged some C code which appeared to work but in less than a day the sensor would stop responding. The code seemed OK based on the somewhat cryptic datasheet the hobby supply sites provide. But some more digging found a more thorough protocol description on the waveshare web site. Refactoring using the new information resulted in no errors after 48 hours of operation.
Amazon does not allow links to external sites but you can probably find the waveshare page by searching on:
waveshare wiki DHT22_Temperature-Humidity_Sensor
In case that does not work this is the pertinent information:
We will present the steps for data reading in the communication between the host and the sensor.
Step 1
After the AM2302 is powered up (please wait 2s for AM2302 to become stable. In this period, no command will be sent out on device reading.), the sensor tests the environment temperature and humility and records relative data. When finished, the sensor enters the Sleep mode automatically. And the SDA data line of AM2302 is pulled up and remains HIGH as the effect of the pull-up resistor. At this moment, the pin SDA of AM2302 is in the INPUT state, detecting any possible external signal.
Step 2
The Microprocessor I/O is set to OUTPUT and outputs a LOW level for more than 800us (The typical hold time is 1ms). Then, the microprocessor I/O is set to INPUT and the bus will be released. At this moment, the microprocessor I/O (the SDA data line of AM2302) goes HIGH as the effect of the pull-up resistor. After the host released the bus, AM2302 sends out a response, a LOW level of 80ms, and then outputs a HIGH level of 80ms to inform the peripheral to receive data. The signal transmission is shown as below:
IMAGE OMITTED - see web page
Step 3
After the AM2302 sends the response, the SDA outputs a string of 40 bits serial data continuously and the microprocessor receives the data according to the changes of I/O level.
Bit data "0" signal: the level is LOW for 50ms and HIGH for 26-28ms;
Bit data "1" signal: the level is LOW for 50ms and HIGH for 70ms;
The relative signal diagram is shown below:
IMAGE OMITTED - see web page
After the SDA of AM2302 outputted the 40 bits of data, it remains LOW level for 50ms, and then switches to INPUT state and goes HIGH as the effect of the pull-up resistor. At the same time, the AM2302 internally re-tests the environmental temperature and humidity and records the relative data. When finished, the MCU will enter the Sleep mode automatically. Only when the MCU receives the new start signal from the host, the sensor will wake up and enter the working state.
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Product Description
2 PCS DHT22 Temperature Humidity Sensor Module Digital Measurement for Arduino Raspberry Pi 2 3
With fixing screw hole, convenient for install and fixed
Single-bus digital signal output, bidirectional serial data
Operate Voltage: DC 3~5.5V
Temperature Range: -40 ℃ ~ 80 ℃
Humidity Range: 0~100%RH
Feature
- DHT22 digital temperature and humidity sensor is a calibrated digital signal output temperature and humidity combined sensor, which application-specific modules capture technology and digital temperature and humidity sensor technology to ensure that products with high reliability and excellent long-term stability.
- No pullup resistor needed. Just plug right into your board.
- Ultra-low power consumption
- No additional components
- Excellent long-term stability
- Single-bus digital signal output, bidirectional serial data
- Completely interchangeable
Package included
2* DHT22/AM2302 Digital Temperature Humidity Sensor Module
2* DuPont wire
This dependable device is great with the Temperature, but seems to be 10% lower on humidity readings
Reviewed in the United States on July 12, 2019
This handy device is the mainstay of anybody learning to play with microcontrollers. Everyone wants to be able to read humidity and temperature and this device will do it just fine. I love that they soldered in the pins and even gave me a cable. It appears to already have any drop down resistors so I dont have to add them to my project. I like the cable because I can stretch the sensor away from my hardware to take more accurate readings. I find that the humidity readings are about 10% off so, for example, if your humidity is 64% this device will read 54%. but who cares? You're not NASA and lives do not hang in the balance. If it is annoying enough just burp your code.This device runs just fine on my 3.3 ESP-32 Micro controller and having the convenience of 2 devices makes it so I can make multiple sensors!
Reviewed in the United States on July 12, 2019
Images in this review
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This dependable device is great with the Temperature, but seems to be 10% lower on humidity readings
Reviewed in the United States 🇺🇸 on July 12, 2019
This dependable device is great with the Temperature, but seems to be 10% lower on humidity readings
Reviewed in the United States 🇺🇸 on July 12, 2019
This handy device is the mainstay of anybody learning to play with microcontrollers. Everyone wants to be able to read humidity and temperature and this device will do it just fine. I love that they soldered in the pins and even gave me a cable. It appears to already have any drop down resistors so I dont have to add them to my project. I like the cable because I can stretch the sensor away from my hardware to take more accurate readings. I find that the humidity readings are about 10% off so, for example, if your humidity is 64% this device will read 54%. but who cares? You're not NASA and lives do not hang in the balance. If it is annoying enough just burp your code.Reviewed in the United States 🇺🇸 on July 12, 2019
This device runs just fine on my 3.3 ESP-32 Micro controller and having the convenience of 2 devices makes it so I can make multiple sensors!
Images in this review
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