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BeagleBone_PRU_DHT11_DHT22

==========================

Read DHT11/22 temperature and humidity sensor from the Beaglebone PRU

  • This project was adapted from example apps at git://github.com/beagleboard/am335x_pru_package.git
  • The sensor is connected to P8_12
  • The PRU initiates a read from the sensor and polls the pin, clocking in the response
  • The high time and low time in microseconds of each bit (one start bit plus 40 data bits) is recorded in shared RAM.
  • The low time of the data bits should always be about 50 us
  • If the high time is 28 us, then the bit is a zero
  • If the high time is 70 us, the the bit is a one
  • I'm using 40 us as the cutoff to classify bits as zero or one
  • After the PRU reads the sensor data into shared RAM it halts.
  • The C code analyzes the results in RAM and prints a bunch of debugging info.

Example Output:

Result: 0 -- Low: 66, High: 69  //this is the start bit -- should be 80 us high, 80 us low

Result: 1 -- Low: 43, High: 19  // 0
Result: 2 -- Low: 43, High: 19  // 0
Result: 3 -- Low: 43, High: 56  // 1
Result: 4 -- Low: 44, High: 18  // 0
Result: 5 -- Low: 44, High: 19  // 0
Result: 6 -- Low: 43, High: 56  // 1
Result: 7 -- Low: 43, High: 57  // 1
Result: 8 -- Low: 43, High: 19  // 0 (0x26 or 38 in decimal)

Result: 9 -- Low: 43, High: 19
Result: 10 -- Low: 43, High: 19
Result: 11 -- Low: 43, High: 19
Result: 12 -- Low: 43, High: 19
Result: 13 -- Low: 43, High: 19
Result: 14 -- Low: 44, High: 18
Result: 15 -- Low: 44, High: 19
Result: 16 -- Low: 43, High: 20  // all zeros

Result: 17 -- Low: 43, High: 19
Result: 18 -- Low: 43, High: 19
Result: 19 -- Low: 43, High: 19
Result: 20 -- Low: 43, High: 57
Result: 21 -- Low: 43, High: 19
Result: 22 -- Low: 43, High: 56
Result: 23 -- Low: 44, High: 56
Result: 24 -- Low: 43, High: 56  // (0x17 or 23 in decimal)

Result: 25 -- Low: 44, High: 19
Result: 26 -- Low: 43, High: 19
Result: 27 -- Low: 43, High: 19
Result: 28 -- Low: 43, High: 19
Result: 29 -- Low: 43, High: 19
Result: 30 -- Low: 43, High: 19
Result: 31 -- Low: 43, High: 19
Result: 32 -- Low: 43, High: 21  // all zeros

Result: 33 -- Low: 43, High: 19
Result: 34 -- Low: 43, High: 19
Result: 35 -- Low: 43, High: 56
Result: 36 -- Low: 43, High: 57
Result: 37 -- Low: 43, High: 56
Result: 38 -- Low: 44, High: 56
Result: 39 -- Low: 43, High: 19
Result: 40 -- Low: 43, High: 55  // (0x3d or 61 in decimal)

Byte: 1 -- 38
Byte: 2 -- 0
Byte: 3 -- 23
Byte: 4 -- 0
Byte: 5 -- 61
Example executed successfully.

This means Humidity is 38.0%, Temperature is 23.0 degrees C, and the checksum is correct (38 + 0 + 23 + 0 = 61)

I tested on a Beaglebone Black A6 with a DHT11 on pin P8_12

You will need to enable the PRU in the device tree (by loading a device tree overlay for example) before running the code.