Modbus - Gas Detector Bricklet

Note

This Bricklet is currently in the prototype stage and the software/hardware as well as the documentation is in an incomplete state.

This is the description of the Modbus protocol for the Gas Detector Bricklet. General information and technical specifications for the Gas Detector Bricklet are summarized in its hardware description.

API

A general description of the Modbus protocol structure can be found here.

Basic Functions

BrickletGasDetector.get_value
Function ID:

1

Request:

empty payload

Response:
  • value -- uint16

Returns a value between 0 and 4095.

See here for more information about the measurements.

If you want to get the value periodically, it is recommended to use the callback CALLBACK_VALUE and set the period with set_value_callback_period.

Advanced Functions

BrickletGasDetector.set_moving_average
Function ID:

8

Request:
  • average -- uint8
Response:

no response

Sets the length of a moving averaging for the measured value.

Setting the length to 1 will turn the averaging off. With less averaging, there is more noise on the data.

The range for the averaging is 1-100.

The default value is 100.

BrickletGasDetector.get_moving_average
Function ID:

9

Request:

empty payload

Response:
  • average -- uint8

Returns the length moving average as set by set_moving_average.

BrickletGasDetector.set_detector_type
Function ID:

10

Request:
  • detector_type -- uint8
Response:

no response

Sets the detector type.

The following types are currently supported.

  • Type 0: MQ2 and MQ5
  • Type 1: MQ3

The detector type is written to the EEPROM of the Bricklet, so it only has to be set once.

You can use the Brick Viewer to set the detector type, so you likely don't need to use this function in your source code.

The default detector type is 0.

BrickletGasDetector.get_detector_type
Function ID:

11

Request:

empty payload

Response:
  • detector_type -- uint8

Returns the detector type as set by set_detector_type.

BrickletGasDetector.heater_on
Function ID:12
Request:empty payload
Response:no response

Turns the internal heater on.

BrickletGasDetector.heater_off
Function ID:13
Request:empty payload
Response:no response

Turns the internal heater off.

BrickletGasDetector.is_heater_on
Function ID:

14

Request:

empty payload

Response:
  • heater -- bool

Returns true if the heater is on, false otherwise.

BrickletGasDetector.get_identity
Function ID:

255

Request:

empty payload

Response:
  • uid -- char[8]
  • connected_uid -- char[8]
  • position -- char
  • hardware_version -- uint8[3]
  • firmware_version -- uint8[3]
  • device_identifier -- uint16

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here

Callback Configuration Functions

BrickletGasDetector.set_value_callback_period
Function ID:

2

Request:
  • period -- uint32
Response:

no response

Sets the period in ms with which the CALLBACK_VALUE callback is triggered periodically. A value of 0 turns the callback off.

CALLBACK_VALUE is only triggered if the value value has changed since the last triggering.

The default value is 0.

BrickletGasDetector.get_value_callback_period
Function ID:

3

Request:

empty payload

Response:
  • period -- uint32

Returns the period as set by set_value_callback_period.

BrickletGasDetector.set_value_callback_threshold
Function ID:

4

Request:
  • option -- char
  • min -- uint16
  • max -- uint16
Response:

no response

Sets the thresholds for the CALLBACK_VALUE_REACHED callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the value value is outside the min and max values
'i' Callback is triggered when the value value is inside the min and max values
'<' Callback is triggered when the value value is smaller than the min value (max is ignored)
'>' Callback is triggered when the value value is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

BrickletGasDetector.get_value_callback_threshold
Function ID:

5

Request:

empty payload

Response:
  • option -- char
  • min -- uint16
  • max -- uint16

Returns the threshold as set by set_value_callback_threshold.

BrickletGasDetector.set_debounce_period
Function ID:

6

Request:
  • debounce -- uint32
Response:

no response

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

BrickletGasDetector.get_debounce_period
Function ID:

7

Request:

empty payload

Response:
  • debounce -- uint32

Returns the debounce period as set by set_debounce_period.

Callbacks

BrickletGasDetector.CALLBACK_VALUE
Function ID:

15

Response:
  • value -- uint16

This callback is triggered periodically with the period that is set by set_value_callback_period. The response value is the value value of the sensor.

CALLBACK_VALUE is only triggered if the value has changed since the last triggering.

BrickletGasDetector.CALLBACK_VALUE_REACHED
Function ID:

16

Response:
  • value -- uint16

This callback is triggered when the threshold as set by set_value_callback_threshold is reached. The response value is the value of the detector.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by set_debounce_period.

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