MQTT - Thermocouple Bricklet

This is the description of the MQTT API bindings for the Thermocouple Bricklet. General information and technical specifications for the Thermocouple Bricklet are summarized in its hardware description.

An installation guide for the MQTT API bindings is part of their general description.

Examples

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

Simple

Download (example-simple.txt)

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# Change XYZ to the UID of your Thermocouple Bricklet

setup:
    # Get current temperature
    subscribe to tinkerforge/response/thermocouple_bricklet/XYZ/get_temperature
    publish '' to tinkerforge/request/thermocouple_bricklet/XYZ/get_temperature

Callback

Download (example-callback.txt)

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# Change XYZ to the UID of your Thermocouple Bricklet

setup:
    # Handle incoming temperature callbacks
    subscribe to tinkerforge/callback/thermocouple_bricklet/XYZ/temperature
    publish '{"register": true}' to tinkerforge/register/thermocouple_bricklet/XYZ/temperature # Register temperature callback

    # Set period for temperature callback to 1s (1000ms)
    # Note: The temperature callback is only called every second
    #       if the temperature has changed since the last call!
    publish '{"period": 1000}' to tinkerforge/request/thermocouple_bricklet/XYZ/set_temperature_callback_period

Threshold

Download (example-threshold.txt)

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# Change XYZ to the UID of your Thermocouple Bricklet

setup:
    # Get threshold callbacks with a debounce time of 10 seconds (10000ms)
    publish '{"debounce": 10000}' to tinkerforge/request/thermocouple_bricklet/XYZ/set_debounce_period

    # Handle incoming temperature reached callbacks
    subscribe to tinkerforge/callback/thermocouple_bricklet/XYZ/temperature_reached
    publish '{"register": true}' to tinkerforge/register/thermocouple_bricklet/XYZ/temperature_reached # Register temperature_reached callback

    # Configure threshold for temperature "greater than 30 °C"
    publish '{"option": "greater", "min": 3000, "max": 0}' to tinkerforge/request/thermocouple_bricklet/XYZ/set_temperature_callback_threshold

API

All published payloads to and from the MQTT bindings are in JSON format.

If an error occures, the bindings publish a JSON object containing the error message as member _ERROR. It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

Basic Functions

request/thermocouple_bricklet/<UID>/get_temperature
Request:
  • empty payload
Response:
  • temperature – Type: int, Unit: 1/100 °C, Range: [-21000 to 180000]

Returns the temperature of the thermocouple.

If you want to get the temperature periodically, it is recommended to use the register/thermocouple_bricklet/<UID>/temperature callback and set the period with request/thermocouple_bricklet/<UID>/set_temperature_callback_period.

Advanced Functions

request/thermocouple_bricklet/<UID>/set_configuration
Request:
  • averaging – Type: int, Range: See symbols, Default: 16
  • thermocouple_type – Type: int, Range: See symbols, Default: 3
  • filter – Type: int, Range: See symbols, Default: 0
Response:
  • no response

You can configure averaging size, thermocouple type and frequency filtering.

Available averaging sizes are 1, 2, 4, 8 and 16 samples.

As thermocouple type you can use B, E, J, K, N, R, S and T. If you have a different thermocouple or a custom thermocouple you can also use G8 and G32. With these types the returned value will not be in °C/100, it will be calculated by the following formulas:

  • G8: value = 8 * 1.6 * 2^17 * Vin
  • G32: value = 32 * 1.6 * 2^17 * Vin

where Vin is the thermocouple input voltage.

The frequency filter can be either configured to 50Hz or to 60Hz. You should configure it according to your utility frequency.

The conversion time depends on the averaging and filter configuration, it can be calculated as follows:

  • 60Hz: time = 82 + (samples - 1) * 16.67
  • 50Hz: time = 98 + (samples - 1) * 20

The following symbols are available for this function:

For averaging:

  • "1" = 1
  • "2" = 2
  • "4" = 4
  • "8" = 8
  • "16" = 16

For thermocouple_type:

  • "b" = 0
  • "e" = 1
  • "j" = 2
  • "k" = 3
  • "n" = 4
  • "r" = 5
  • "s" = 6
  • "t" = 7
  • "g8" = 8
  • "g32" = 9

For filter:

  • "50hz" = 0
  • "60hz" = 1
request/thermocouple_bricklet/<UID>/get_configuration
Request:
  • empty payload
Response:
  • averaging – Type: int, Range: See symbols, Default: 16
  • thermocouple_type – Type: int, Range: See symbols, Default: 3
  • filter – Type: int, Range: See symbols, Default: 0

Returns the configuration as set by request/thermocouple_bricklet/<UID>/set_configuration.

The following symbols are available for this function:

For averaging:

  • "1" = 1
  • "2" = 2
  • "4" = 4
  • "8" = 8
  • "16" = 16

For thermocouple_type:

  • "b" = 0
  • "e" = 1
  • "j" = 2
  • "k" = 3
  • "n" = 4
  • "r" = 5
  • "s" = 6
  • "t" = 7
  • "g8" = 8
  • "g32" = 9

For filter:

  • "50hz" = 0
  • "60hz" = 1
request/thermocouple_bricklet/<UID>/get_error_state
Request:
  • empty payload
Response:
  • over_under – Type: bool
  • open_circuit – Type: bool

Returns the current error state. There are two possible errors:

  • Over/Under Voltage and
  • Open Circuit.

Over/Under Voltage happens for voltages below 0V or above 3.3V. In this case it is very likely that your thermocouple is defective. An Open Circuit error indicates that there is no thermocouple connected.

You can use the register/thermocouple_bricklet/<UID>/error_state callback to automatically get triggered when the error state changes.

request/thermocouple_bricklet/<UID>/get_identity
Request:
  • empty payload
Response:
  • uid – Type: string, Length: up to 8
  • connected_uid – Type: string, Length: up to 8
  • position – Type: char, Range: ["a" to "h", "i", "z"]
  • hardware_version – Type: [int, ...], Length: 3
    • 0: major – Type: int, Range: [0 to 255]
    • 1: minor – Type: int, Range: [0 to 255]
    • 2: revision – Type: int, Range: [0 to 255]
  • firmware_version – Type: [int, ...], Length: 3
    • 0: major – Type: int, Range: [0 to 255]
    • 1: minor – Type: int, Range: [0 to 255]
    • 2: revision – Type: int, Range: [0 to 255]
  • device_identifier – Type: int, Range: [0 to 216 - 1]
  • _display_name – Type: string

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', 'd', 'e', 'f', 'g' or 'h' (Bricklet Port). The Raspberry Pi HAT (Zero) Brick is always at position 'i' and the Bricklet connected to an Isolator Bricklet is always as position 'z'.

The device identifier numbers can be found here. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the Thermocouple's name in a human readable form.

Callback Configuration Functions

request/thermocouple_bricklet/<UID>/set_temperature_callback_period
Request:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
Response:
  • no response

Sets the period with which the register/thermocouple_bricklet/<UID>/temperature callback is triggered periodically. A value of 0 turns the callback off.

The register/thermocouple_bricklet/<UID>/temperature callback is only triggered if the temperature has changed since the last triggering.

request/thermocouple_bricklet/<UID>/get_temperature_callback_period
Request:
  • empty payload
Response:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0

Returns the period as set by request/thermocouple_bricklet/<UID>/set_temperature_callback_period.

request/thermocouple_bricklet/<UID>/set_temperature_callback_threshold
Request:
  • option – Type: char, Range: See symbols, Default: "x"
  • min – Type: int, Unit: 1/100 °C, Range: [-231 to 231 - 1], Default: 0
  • max – Type: int, Unit: 1/100 °C, Range: [-231 to 231 - 1], Default: 0
Response:
  • no response

Sets the thresholds for the register/thermocouple_bricklet/<UID>/temperature_reached callback.

The following options are possible:

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

The following symbols are available for this function:

For option:

  • "off" = "x"
  • "outside" = "o"
  • "inside" = "i"
  • "smaller" = "<"
  • "greater" = ">"
request/thermocouple_bricklet/<UID>/get_temperature_callback_threshold
Request:
  • empty payload
Response:
  • option – Type: char, Range: See symbols, Default: "x"
  • min – Type: int, Unit: 1/100 °C, Range: [-231 to 231 - 1], Default: 0
  • max – Type: int, Unit: 1/100 °C, Range: [-231 to 231 - 1], Default: 0

Returns the threshold as set by request/thermocouple_bricklet/<UID>/set_temperature_callback_threshold.

The following symbols are available for this function:

For option:

  • "off" = "x"
  • "outside" = "o"
  • "inside" = "i"
  • "smaller" = "<"
  • "greater" = ">"
request/thermocouple_bricklet/<UID>/set_debounce_period
Request:
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100
Response:
  • no response

Sets the period with which the threshold callback

is triggered, if the threshold

keeps being reached.

request/thermocouple_bricklet/<UID>/get_debounce_period
Request:
  • empty payload
Response:
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100

Returns the debounce period as set by request/thermocouple_bricklet/<UID>/set_debounce_period.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.

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.

register/thermocouple_bricklet/<UID>/temperature
Register Request:
  • register – Type: bool
Callback Response:
  • temperature – Type: int, Unit: 1/100 °C, Range: [-21000 to 180000]

A callback can be registered for this event by publishing to the .../register/thermocouple_bricklet/<UID>/temperature[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/thermocouple_bricklet/<UID>/temperature[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/thermocouple_bricklet/<UID>/set_temperature_callback_period. The callback payload is the temperature of the thermocouple.

The register/thermocouple_bricklet/<UID>/temperature callback is only triggered if the temperature has changed since the last triggering.

register/thermocouple_bricklet/<UID>/temperature_reached
Register Request:
  • register – Type: bool
Callback Response:
  • temperature – Type: int, Unit: 1/100 °C, Range: [-21000 to 180000]

A callback can be registered for this event by publishing to the .../register/thermocouple_bricklet/<UID>/temperature_reached[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/thermocouple_bricklet/<UID>/temperature_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when the threshold as set by request/thermocouple_bricklet/<UID>/set_temperature_callback_threshold is reached. The callback payload is the temperature of the thermocouple.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by request/thermocouple_bricklet/<UID>/set_debounce_period.

register/thermocouple_bricklet/<UID>/error_state
Register Request:
  • register – Type: bool
Callback Response:
  • over_under – Type: bool
  • open_circuit – Type: bool

A callback can be registered for this event by publishing to the .../register/thermocouple_bricklet/<UID>/error_state[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/thermocouple_bricklet/<UID>/error_state[/<SUFFIX>] topic for each registered suffix.

This Callback is triggered every time the error state changes (see request/thermocouple_bricklet/<UID>/get_error_state).