59 lines
2.1 KiB
Plaintext
59 lines
2.1 KiB
Plaintext
= DHT-11, DHT-22, and AM2302 Sensors
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:xrefstyle: short
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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.
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[NOTE]
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======
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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.
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======
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== Wiring information
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See <<dht-wiring-diagram>> for wiring instructions.
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[[dht-wiring-diagram]]
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[pdfwidth=75%]
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.Wiring the DHT-22 temperature sensor to Raspberry Pi Pico, and connecting Pico's UART0 to the Raspberry Pi 4.
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image::pi-and-pico-uart-and-dht-sensor.png[]
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NOTE: One of the pins (pin 3) on the DHT sensor will not be connected, it is not used.
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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.
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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.
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[[dht-serial-output-diagram]]
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[pdfwidth=75%]
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.Serial output over Pico's UART0 in a terminal window.
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image::serial-output.png[]
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Connect to `/dev/serial0` by typing,
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----
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$ minicom -b 115200 -o -D /dev/serial0
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----
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at the command line.
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== List of Files
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A list of files with descriptions of their function;
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CMakeLists.txt:: Make file to incorporate the example in to the examples build tree.
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dht.c:: The example code.
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== Bill of Materials
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.A list of materials required for the example
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[[dht-22-bom-table]]
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[cols=3]
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|===
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| *Item* | *Quantity* | Details
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| Breadboard | 1 | generic part
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| Raspberry Pi Pico | 1 | https://www.raspberrypi.com/products/raspberry-pi-pico/
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| 10 kΩ resistor | 1 | generic part
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| M/M Jumper wires | 4 | generic part
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| DHT-22 sensor | 1 | generic part
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|===
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