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DHT Sensor Feature

Provide support for connecting a DHT sensor like this one (also works with DHT11). These sensors require a special driver on the board, because the communication protocol is very timing critical, so that reading the sensor from the host using GPIO commands will not work.

Current implementation supports only one DHT sensor, but the protocol supports more.

[Implementation Note: Currently, the sampling interval is ignored and a single reply sent. Since the minimum cycle time for these sensors is in the order of 2.5s, polling is not an issue]

Example files:

Compatible client libraries

Tested boards

This feature has been tested with a DHT11 sensor on:

  • Arduino Uno
  • Arduino Nano

Protocol details

The protocol below use exclusively SysEx queries and SysEx responses.

Attach sensor

Query :

0 START_SYSEX                (0xF0)
1 DHTSENSOR_DATA             (0x74)
2 DHTSENSOR_ATTACH_DHT22     (0x02) [for DHT11 sensors use DHTSENSOR_ATTACH_DHT11 (0x01)]
3 pin                        (0-127)
4 blocking reads             (0-1) [optional - enables an 18ms blocking call when starting the read **use with caution**. default: 0 (disabled)]
5 sampling interval          (lsb) [optional - sampling interval to report sensor data (in ms). minimum: 500ms. default: 500ms.]
... additional bytes may be sent if more bits are needed
N END_SYSEX                  (0xF7)

At least one response is sent.

Report sensor data

No Query, report is done automatically on the requested interval

Response

0 START_SYSEX                (0xF0)
1 DHTSENSOR_DATA             (0x74)
2 DHTSENSOR_RESPONSE         (0x00)
3 pin                        (0-127)
4 temperature, bits 0-6      (lsb - temperature in Celsius * 10)
5 temperature, bits 7-13     (msb - temperature in Celsius * 10)
6 humidity, bits 0-6         (lsb - relative humidity in % * 10)
7 humidity, bits 7-13        (msb - relative humidity in % * 10)
N END_SYSEX                  (0xF7)

Note:

Temperature

  • Range: -40~80 ºC
  • Resolution: 0.1 ºC
  • Accuracy: <0.5 ºC

Humidity

  • Range: 0-100 %RH
  • Resolution: 0.1 %RH
  • Accuracy: +-2 %RH (Max +-5 %RH)

Detach sensor

Query :

0 START_SYSEX                (0xF0)
1 DHTSENSOR_DATA             (0x74)
2 DHTSENSOR_DETACH           (0x03)
3 pin                        (0-127)
4 END_SYSEX                  (0xF7)

No response.