C/C++ - 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 C/C++ API bindings for the Gas Detector Bricklet. General information and technical specifications for the Gas Detector Bricklet are summarized in its hardware description.

An installation guide for the C/C++ API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

API

Every function of the C/C++ bindings returns an integer which describes an error code. Data returned from the device, when a getter is called, is handled via call by reference. These parameters are labeled with the ret_ prefix.

Possible error codes are:

  • E_OK = 0
  • E_TIMEOUT = -1
  • E_NO_STREAM_SOCKET = -2
  • E_HOSTNAME_INVALID = -3
  • E_NO_CONNECT = -4
  • E_NO_THREAD = -5
  • E_NOT_ADDED = -6 (unused since bindings version 2.0.0)
  • E_ALREADY_CONNECTED = -7
  • E_NOT_CONNECTED = -8
  • E_INVALID_PARAMETER = -9
  • E_NOT_SUPPORTED = -10
  • E_UNKNOWN_ERROR_CODE = -11

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void gas_detector_create(GasDetector *gas_detector, const char *uid, IPConnection *ipcon)

Creates the device object gas_detector with the unique device ID uid and adds it to the IPConnection ipcon:

GasDetector gas_detector;
gas_detector_create(&gas_detector, "YOUR_DEVICE_UID", &ipcon);

This device object can be used after the IP connection has been connected (see examples above).

void gas_detector_destroy(GasDetector *gas_detector)

Removes the device object gas_detector from its IPConnection and destroys it. The device object cannot be used anymore afterwards.

int gas_detector_get_value(GasDetector *gas_detector, uint16_t *ret_value)

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 GAS_DETECTOR_CALLBACK_VALUE and set the period with gas_detector_set_value_callback_period().

Advanced Functions

int gas_detector_set_moving_average(GasDetector *gas_detector, uint8_t average)

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.

int gas_detector_get_moving_average(GasDetector *gas_detector, uint8_t *ret_average)

Returns the length moving average as set by gas_detector_set_moving_average().

int gas_detector_set_detector_type(GasDetector *gas_detector, uint8_t detector_type)

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.

The following defines are available for this function:

  • GAS_DETECTOR_DETECTOR_TYPE_0 = 0
  • GAS_DETECTOR_DETECTOR_TYPE_1 = 1
int gas_detector_get_detector_type(GasDetector *gas_detector, uint8_t *ret_detector_type)

Returns the detector type as set by gas_detector_set_detector_type().

The following defines are available for this function:

  • GAS_DETECTOR_DETECTOR_TYPE_0 = 0
  • GAS_DETECTOR_DETECTOR_TYPE_1 = 1
int gas_detector_heater_on(GasDetector *gas_detector)

Turns the internal heater on.

int gas_detector_heater_off(GasDetector *gas_detector)

Turns the internal heater off.

int gas_detector_is_heater_on(GasDetector *gas_detector, bool *ret_heater)

Returns true if the heater is on, false otherwise.

int gas_detector_get_api_version(GasDetector *gas_detector, uint8_t ret_api_version[3])

Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

int gas_detector_get_response_expected(GasDetector *gas_detector, uint8_t function_id, bool *ret_response_expected)

Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by gas_detector_set_response_expected(). For setter functions it is disabled by default and can be enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

See gas_detector_set_response_expected() for the list of function ID defines available for this function.

int gas_detector_set_response_expected(GasDetector *gas_detector, uint8_t function_id, bool response_expected)

Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled and callbacks it is always disabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

The following function ID defines are available for this function:

  • GAS_DETECTOR_FUNCTION_SET_VALUE_CALLBACK_PERIOD = 2
  • GAS_DETECTOR_FUNCTION_SET_VALUE_CALLBACK_THRESHOLD = 4
  • GAS_DETECTOR_FUNCTION_SET_DEBOUNCE_PERIOD = 6
  • GAS_DETECTOR_FUNCTION_SET_MOVING_AVERAGE = 8
  • GAS_DETECTOR_FUNCTION_SET_DETECTOR_TYPE = 10
  • GAS_DETECTOR_FUNCTION_HEATER_ON = 12
  • GAS_DETECTOR_FUNCTION_HEATER_OFF = 13
int gas_detector_set_response_expected_all(GasDetector *gas_detector, bool response_expected)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

int gas_detector_get_identity(GasDetector *gas_detector, char ret_uid[8], char ret_connected_uid[8], char *ret_position, uint8_t ret_hardware_version[3], uint8_t ret_firmware_version[3], uint16_t *ret_device_identifier)

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. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

void gas_detector_register_callback(GasDetector *gas_detector, uint8_t id, void *callback, void *user_data)

Registers a callback with ID id to the function callback. The user_data will be given as a parameter of the callback.

The available IDs with corresponding function signatures are listed below.

int gas_detector_set_value_callback_period(GasDetector *gas_detector, uint32_t period)

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

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

The default value is 0.

int gas_detector_get_value_callback_period(GasDetector *gas_detector, uint32_t *ret_period)

Returns the period as set by gas_detector_set_value_callback_period().

int gas_detector_set_value_callback_threshold(GasDetector *gas_detector, char option, uint16_t min, uint16_t max)

Sets the thresholds for the GAS_DETECTOR_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).

The following defines are available for this function:

  • GAS_DETECTOR_THRESHOLD_OPTION_OFF = 'x'
  • GAS_DETECTOR_THRESHOLD_OPTION_OUTSIDE = 'o'
  • GAS_DETECTOR_THRESHOLD_OPTION_INSIDE = 'i'
  • GAS_DETECTOR_THRESHOLD_OPTION_SMALLER = '<'
  • GAS_DETECTOR_THRESHOLD_OPTION_GREATER = '>'
int gas_detector_get_value_callback_threshold(GasDetector *gas_detector, char *ret_option, uint16_t *ret_min, uint16_t *ret_max)

Returns the threshold as set by gas_detector_set_value_callback_threshold().

The following defines are available for this function:

  • GAS_DETECTOR_THRESHOLD_OPTION_OFF = 'x'
  • GAS_DETECTOR_THRESHOLD_OPTION_OUTSIDE = 'o'
  • GAS_DETECTOR_THRESHOLD_OPTION_INSIDE = 'i'
  • GAS_DETECTOR_THRESHOLD_OPTION_SMALLER = '<'
  • GAS_DETECTOR_THRESHOLD_OPTION_GREATER = '>'
int gas_detector_set_debounce_period(GasDetector *gas_detector, uint32_t debounce)

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

int gas_detector_get_debounce_period(GasDetector *gas_detector, uint32_t *ret_debounce)

Returns the debounce period as set by gas_detector_set_debounce_period().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the gas_detector_register_callback() function. The parameters consist of the device object, the callback ID, the callback function and optional user data:

void my_callback(int p, void *user_data) {
    printf("parameter: %d\n", p);
}

gas_detector_register_callback(&gas_detector, GAS_DETECTOR_CALLBACK_EXAMPLE, (void *)my_callback, NULL);

The available constants with corresponding callback function signatures are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

GAS_DETECTOR_CALLBACK_VALUE
void callback(uint16_t value, void *user_data)

This callback is triggered periodically with the period that is set by gas_detector_set_value_callback_period(). The parameter is the value value of the sensor.

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

GAS_DETECTOR_CALLBACK_VALUE_REACHED
void callback(uint16_t value, void *user_data)

This callback is triggered when the threshold as set by gas_detector_set_value_callback_threshold() is reached. The parameter is the value of the detector.

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

Constants

GAS_DETECTOR_DEVICE_IDENTIFIER

This constant is used to identify a Gas Detector Bricklet.

The gas_detector_get_identity() function and the IPCON_CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

Creative Commons Licence The content of this page is licensed under Creative Commons Attribution 3.0 Unported License.