dht_sensor

DHT-11, DHT-22, and AM2302 Sensors

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 Figure 1 for wiring instructions.

Figure 1. Wiring the DHT-22 temperature sensor to Raspberry Pi Pico, and connecting Pico’s UART0 to the Raspberry Pi 4.

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 Figure 1 and you should see something similar to Figure 2 in minicom when connected to /dev/serial0 on the Raspberry Pi.

Figure 2. Serial output over Pico’s UART0 in a terminal window.

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

Table 1. A list of materials required for the example

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