= DHT-11, DHT-22, and AM2302 Sensors :xrefstyle: short The DHT sensors are fairly well known hobbyist sensors for measuring relative humidity and temperature using a capacitive humidity sensor, and a thermistor. While they are slow, one reading every ~2 seconds, they are reliable and good for basic data logging. Communication is based on a custom protocol which uses a single wire for data. [NOTE] ====== The DHT-11 and DHT-22 sensors are the most common. They use the same protocol but have different characteristics, the DHT-22 has better accuracy, and has a larger sensor range than the DHT-11. The sensor is available from a number of retailers. ====== == Wiring information See <<dht-wiring-diagram>> for wiring instructions. [[dht-wiring-diagram]] [pdfwidth=75%] .Wiring the DHT-22 temperature sensor to Raspberry Pi Pico, and connecting Pico's UART0 to the Raspberry Pi 4. image::pi-and-pico-uart-and-dht-sensor.png[] NOTE: One of the pins (pin 3) on the DHT sensor will not be connected, it is not used. You will want to place a 10 kΩ resistor between VCC and the data pin, to act as a medium-strength pull up on the data line. Connecting UART0 of Pico to Raspberry Pi as in <<dht-wiring-diagram>> and you should see something similar to <<dht-serial-output-diagram>> in `minicom` when connected to `/dev/serial0` on the Raspberry Pi. [[dht-serial-output-diagram]] [pdfwidth=75%] .Serial output over Pico's UART0 in a terminal window. image::serial-output.png[] Connect to `/dev/serial0` by typing, ---- $ minicom -b 115200 -o -D /dev/serial0 ---- at the command line. == List of Files A list of files with descriptions of their function; CMakeLists.txt:: Make file to incorporate the example in to the examples build tree. dht.c:: The example code. == Bill of Materials .A list of materials required for the example [[dht-22-bom-table]] [cols=3] |=== | *Item* | *Quantity* | Details | Breadboard | 1 | generic part | Raspberry Pi Pico | 1 | https://www.raspberrypi.com/products/raspberry-pi-pico/ | 10 kΩ resistor | 1 | generic part | M/M Jumper wires | 4 | generic part | DHT-22 sensor | 1 | generic part |===