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DHT11

Arduino library to read temperatur and humidity of DHT11 sensor. This library improves on my previous Arduino sketch based solutions DHT11Light and DHT11Tiny.

Working principle and 1 MHz challenge solved

The DHT11 sends a sequence of long and short high signal pulses. Long means 1, short means 0.

This library is able to get correct readings when running the AVR chip at 1 MHz. In my previous sketches this proved to be a challenge.

1 MHz optimizations

  • turn off interrupts during reading
  • count the number of cycles of the high signal in loop cycles
  • poll pin state with register (PINB / PIND) lookup instead of digitalRead()

General note on running the chip at 1 MHz: To save power it's wiser to run the chip faster (for instance 8 MHz) and use the sleep modes whenever possible.

Debugging

Debugging of the registered high signal lengths can be turned by on uncommenting this line in DHT11.h:

#define DHT11_DEBUG