MQTT - DC Brick

This is the description of the MQTT API bindings for the DC Brick. General information and technical specifications for the DC Brick 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).

Configuration

Download (example-configuration.txt)

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# Change XXYYZZ to the UID of your DC Brick

setup:
    publish '{"mode": "drive_coast"}' to tinkerforge/request/dc_brick/XXYYZZ/set_drive_mode 
    
    publish '{"frequency": 10000}' to tinkerforge/request/dc_brick/XXYYZZ/set_pwm_frequency  # Use PWM frequency of 10kHz
    
    publish '{"acceleration": 5000}' to tinkerforge/request/dc_brick/XXYYZZ/set_acceleration  # Slow acceleration
    
    publish '{"velocity": 32767}' to tinkerforge/request/dc_brick/XXYYZZ/set_velocity  # Full speed forward
    
    publish '' to tinkerforge/request/dc_brick/XXYYZZ/enable  # Enable motor power

cleanup:
    # If you are done, run this to clean up
    publish '' to tinkerforge/request/dc_brick/XXYYZZ/disable  # Disable motor power

Callback

Download (example-callback.txt)

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# Change XXYYZZ to the UID of your DC Brick

setup:
    # The acceleration has to be smaller or equal to the maximum
    # acceleration of the DC motor, otherwise the velocity reached
    # callback will be called too early
    publish '{"acceleration": 5000}' to tinkerforge/request/dc_brick/XXYYZZ/set_acceleration  # Slow acceleration
    publish '{"velocity": 32767}' to tinkerforge/request/dc_brick/XXYYZZ/set_velocity  # Full speed forward
    
    # Use velocity reached callback to swing back and forth
    # between full speed forward and full speed backward
    subscribe to tinkerforge/callback/dc_brick/XXYYZZ/velocity_reached
        if a message arrives
            # message contains velocity as int
            if velocity == 32767
                print "Velocity: Full speed forward, now turning backward"
                publish '{"velocity": -32767}' to tinkerforge/request/dc_brick/XXYYZZ/set_velocity
            elseif velocity == -32767
                print "Velocity: Full speed backward, now turning forward"
                publish '{"velocity": 32767}' to tinkerforge/request/dc_brick/XXYYZZ/set_velocity
            else
                print "Error"
            endif
        endif
    endsubscribe
    publish '{"register": true}' to tinkerforge/register/dc_brick/XXYZZ/velocity_reached
    # Enable motor power
    publish '' to tinkerforge/request/dc_brick/XXYYZZ/enable 

cleanup:
    # If you are done, run this to clean up
    publish '' to tinkerforge/request/dc_brick/XXYYZZ/disable  # Disable motor power

API

All published payload to an from the MQTT bindings is in the JSON format.

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

Basic Functions

request/dc_brick/<UID>/set_velocity
Request payload:
 
  • velocity -- int

Sets the velocity of the motor. Whereas -32767 is full speed backward, 0 is stop and 32767 is full speed forward. Depending on the acceleration (see request/dc_brick/<UID>/set_acceleration), the motor is not immediately brought to the velocity but smoothly accelerated.

The velocity describes the duty cycle of the PWM with which the motor is controlled, e.g. a velocity of 3277 sets a PWM with a 10% duty cycle. You can not only control the duty cycle of the PWM but also the frequency, see request/dc_brick/<UID>/set_pwm_frequency.

The default velocity is 0.

request/dc_brick/<UID>/get_velocity
Response payload:
 
  • velocity -- int

Returns the velocity as set by request/dc_brick/<UID>/set_velocity.

request/dc_brick/<UID>/get_current_velocity
Response payload:
 
  • velocity -- int

Returns the current velocity of the motor. This value is different from request/dc_brick/<UID>/get_velocity whenever the motor is currently accelerating to a goal set by request/dc_brick/<UID>/set_velocity.

request/dc_brick/<UID>/set_acceleration
Request payload:
 
  • acceleration -- int

Sets the acceleration of the motor. It is given in velocity/s. An acceleration of 10000 means, that every second the velocity is increased by 10000 (or about 30% duty cycle).

For example: If the current velocity is 0 and you want to accelerate to a velocity of 16000 (about 50% duty cycle) in 10 seconds, you should set an acceleration of 1600.

If acceleration is set to 0, there is no speed ramping, i.e. a new velocity is immediately given to the motor.

The default acceleration is 10000.

request/dc_brick/<UID>/get_acceleration
Response payload:
 
  • acceleration -- int

Returns the acceleration as set by request/dc_brick/<UID>/set_acceleration.

request/dc_brick/<UID>/full_brake

Executes an active full brake.

Warning

This function is for emergency purposes, where an immediate brake is necessary. Depending on the current velocity and the strength of the motor, a full brake can be quite violent.

Call request/dc_brick/<UID>/set_velocity with 0 if you just want to stop the motor.

request/dc_brick/<UID>/enable

Enables the driver chip. The driver parameters can be configured (velocity, acceleration, etc) before it is enabled.

request/dc_brick/<UID>/disable

Disables the driver chip. The configurations are kept (velocity, acceleration, etc) but the motor is not driven until it is enabled again.

request/dc_brick/<UID>/is_enabled
Response payload:
 
  • enabled -- bool

Returns true if the driver chip is enabled, false otherwise.

Advanced Functions

request/dc_brick/<UID>/set_pwm_frequency
Request payload:
 
  • frequency -- int

Sets the frequency (in Hz) of the PWM with which the motor is driven. The possible range of the frequency is 1-20000Hz. Often a high frequency is less noisy and the motor runs smoother. However, with a low frequency there are less switches and therefore fewer switching losses. Also with most motors lower frequencies enable higher torque.

If you have no idea what all this means, just ignore this function and use the default frequency, it will very likely work fine.

The default frequency is 15 kHz.

request/dc_brick/<UID>/get_pwm_frequency
Response payload:
 
  • frequency -- int

Returns the PWM frequency (in Hz) as set by request/dc_brick/<UID>/set_pwm_frequency.

request/dc_brick/<UID>/get_stack_input_voltage
Response payload:
 
  • voltage -- int

Returns the stack input voltage in mV. The stack input voltage is the voltage that is supplied via the stack, i.e. it is given by a Step-Down or Step-Up Power Supply.

request/dc_brick/<UID>/get_external_input_voltage
Response payload:
 
  • voltage -- int

Returns the external input voltage in mV. The external input voltage is given via the black power input connector on the DC Brick.

If there is an external input voltage and a stack input voltage, the motor will be driven by the external input voltage. If there is only a stack voltage present, the motor will be driven by this voltage.

Warning

This means, if you have a high stack voltage and a low external voltage, the motor will be driven with the low external voltage. If you then remove the external connection, it will immediately be driven by the high stack voltage.

request/dc_brick/<UID>/get_current_consumption
Response payload:
 
  • voltage -- int

Returns the current consumption of the motor in mA.

request/dc_brick/<UID>/set_drive_mode
Request payload:
 
  • mode -- int (has symbols)

Sets the drive mode. Possible modes are:

  • 0 = Drive/Brake
  • 1 = Drive/Coast

These modes are different kinds of motor controls.

In Drive/Brake mode, the motor is always either driving or braking. There is no freewheeling. Advantages are: A more linear correlation between PWM and velocity, more exact accelerations and the possibility to drive with slower velocities.

In Drive/Coast mode, the motor is always either driving or freewheeling. Advantages are: Less current consumption and less demands on the motor and driver chip.

The default value is 0 = Drive/Brake.

The following symbols are available for this function:

for mode:

  • "DriveBrake" = 0
  • "DriveCoast" = 1
request/dc_brick/<UID>/get_drive_mode
Response payload:
 
  • mode -- int (has symbols)

Returns the drive mode, as set by request/dc_brick/<UID>/set_drive_mode.

The following symbols are available for this function:

for mode:

  • "DriveBrake" = 0
  • "DriveCoast" = 1
request/dc_brick/<UID>/set_spitfp_baudrate_config
Request payload:
 
  • enable_dynamic_baudrate -- bool
  • minimum_dynamic_baudrate -- int

The SPITF protocol can be used with a dynamic baudrate. If the dynamic baudrate is enabled, the Brick will try to adapt the baudrate for the communication between Bricks and Bricklets according to the amount of data that is transferred.

The baudrate will be increased exponentially if lots of data is send/received and decreased linearly if little data is send/received.

This lowers the baudrate in applications where little data is transferred (e.g. a weather station) and increases the robustness. If there is lots of data to transfer (e.g. Thermal Imaging Bricklet) it automatically increases the baudrate as needed.

In cases where some data has to transferred as fast as possible every few seconds (e.g. RS485 Bricklet with a high baudrate but small payload) you may want to turn the dynamic baudrate off to get the highest possible performance.

The maximum value of the baudrate can be set per port with the function request/dc_brick/<UID>/set_spitfp_baudrate. If the dynamic baudrate is disabled, the baudrate as set by request/dc_brick/<UID>/set_spitfp_baudrate will be used statically.

The minimum dynamic baudrate has a value range of 400000 to 2000000 baud.

By default dynamic baudrate is enabled and the minimum dynamic baudrate is 400000.

New in version 2.3.5 (Firmware).

request/dc_brick/<UID>/get_spitfp_baudrate_config
Response payload:
 
  • enable_dynamic_baudrate -- bool
  • minimum_dynamic_baudrate -- int

Returns the baudrate config, see request/dc_brick/<UID>/set_spitfp_baudrate_config.

New in version 2.3.5 (Firmware).

request/dc_brick/<UID>/get_send_timeout_count
Request payload:
 
  • communication_method -- int (has symbols)
Response payload:
 
  • timeout_count -- int

Returns the timeout count for the different communication methods.

The methods 0-2 are available for all Bricks, 3-7 only for Master Bricks.

This function is mostly used for debugging during development, in normal operation the counters should nearly always stay at 0.

The following symbols are available for this function:

for communication_method:

  • "None" = 0
  • "USB" = 1
  • "SPIStack" = 2
  • "Chibi" = 3
  • "RS485" = 4
  • "WIFI" = 5
  • "Ethernet" = 6
  • "WIFIV2" = 7

New in version 2.3.3 (Firmware).

request/dc_brick/<UID>/set_spitfp_baudrate
Request payload:
 
  • bricklet_port -- string
  • baudrate -- int

Sets the baudrate for a specific Bricklet port ('a' - 'd'). The baudrate can be in the range 400000 to 2000000.

If you want to increase the throughput of Bricklets you can increase the baudrate. If you get a high error count because of high interference (see request/dc_brick/<UID>/get_spitfp_error_count) you can decrease the baudrate.

If the dynamic baudrate feature is enabled, the baudrate set by this function corresponds to the maximum baudrate (see request/dc_brick/<UID>/set_spitfp_baudrate_config).

Regulatory testing is done with the default baudrate. If CE compatibility or similar is necessary in you applications we recommend to not change the baudrate.

The default baudrate for all ports is 1400000.

New in version 2.3.3 (Firmware).

request/dc_brick/<UID>/get_spitfp_baudrate
Request payload:
 
  • bricklet_port -- string
Response payload:
 
  • baudrate -- int

Returns the baudrate for a given Bricklet port, see request/dc_brick/<UID>/set_spitfp_baudrate.

New in version 2.3.3 (Firmware).

request/dc_brick/<UID>/get_spitfp_error_count
Request payload:
 
  • bricklet_port -- string
Response payload:
 
  • error_count_ack_checksum -- int
  • error_count_message_checksum -- int
  • error_count_frame -- int
  • error_count_overflow -- int

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Brick side. All Bricklets have a similar function that returns the errors on the Bricklet side.

New in version 2.3.3 (Firmware).

request/dc_brick/<UID>/enable_status_led

Enables the status LED.

The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

The default state is enabled.

New in version 2.3.1 (Firmware).

request/dc_brick/<UID>/disable_status_led

Disables the status LED.

The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

The default state is enabled.

New in version 2.3.1 (Firmware).

request/dc_brick/<UID>/is_status_led_enabled
Response payload:
 
  • enabled -- bool

Returns true if the status LED is enabled, false otherwise.

New in version 2.3.1 (Firmware).

request/dc_brick/<UID>/get_protocol1_bricklet_name
Request payload:
 
  • port -- string
Response payload:
 
  • protocol_version -- int
  • firmware_version -- [int,int,int]
  • name -- string

Returns the firmware and protocol version and the name of the Bricklet for a given port.

This functions sole purpose is to allow automatic flashing of v1.x.y Bricklet plugins.

request/dc_brick/<UID>/get_chip_temperature
Response payload:
 
  • temperature -- int

Returns the temperature in °C/10 as measured inside the microcontroller. The value returned is not the ambient temperature!

The temperature is only proportional to the real temperature and it has an accuracy of +-15%. Practically it is only useful as an indicator for temperature changes.

request/dc_brick/<UID>/reset

Calling this function will reset the Brick. Calling this function on a Brick inside of a stack will reset the whole stack.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

request/dc_brick/<UID>/get_identity
Response payload:
 
  • uid -- string
  • connected_uid -- string
  • position -- string
  • hardware_version -- [int,int,int]
  • firmware_version -- [int,int,int]
  • device_identifier -- int (has symbols)
  • _display_name -- string

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

The position can be '0'-'8' (stack position).

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 DC's name in a human readable form.

Callback Configuration Functions

request/dc_brick/<UID>/set_minimum_voltage
Request payload:
 
  • voltage -- int

Sets the minimum voltage in mV, below which the register/dc_brick/<UID>/under_voltage callback is triggered. The minimum possible value that works with the DC Brick is 6V. You can use this function to detect the discharge of a battery that is used to drive the motor. If you have a fixed power supply, you likely do not need this functionality.

The default value is 6V.

request/dc_brick/<UID>/get_minimum_voltage
Response payload:
 
  • voltage -- int

Returns the minimum voltage as set by request/dc_brick/<UID>/set_minimum_voltage

request/dc_brick/<UID>/set_current_velocity_period
Request payload:
 
  • period -- int

Sets a period in ms with which the register/dc_brick/<UID>/current_velocity callback is triggered. A period of 0 turns the callback off.

The default value is 0.

request/dc_brick/<UID>/get_current_velocity_period
Response payload:
 
  • period -- int

Returns the period as set by request/dc_brick/<UID>/set_current_velocity_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/dc_brick/<UID>/under_voltage
Request payload:
 
  • register -- bool
Response payload:
 
  • voltage -- int

A callback can be registered for this event by publishing to the .../register/dc_brick/<UID>/under_voltage[/<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/dc_brick/<UID>/under_voltage[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when the input voltage drops below the value set by request/dc_brick/<UID>/set_minimum_voltage. The callback payload is the current voltage given in mV.

register/dc_brick/<UID>/emergency_shutdown
Request payload:
 
  • register -- bool

A callback can be registered for this event by publishing to the .../register/dc_brick/<UID>/emergency_shutdown[/<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/dc_brick/<UID>/emergency_shutdown[/<SUFFIX>] topic for each registered suffix.

This callback is triggered if either the current consumption is too high (above 5A) or the temperature of the driver chip is too high (above 175°C). These two possibilities are essentially the same, since the temperature will reach this threshold immediately if the motor consumes too much current. In case of a voltage below 3.3V (external or stack) this callback is triggered as well.

If this callback is triggered, the driver chip gets disabled at the same time. That means, request/dc_brick/<UID>/enable has to be called to drive the motor again.

Note

This callback only works in Drive/Brake mode (see request/dc_brick/<UID>/set_drive_mode). In Drive/Coast mode it is unfortunately impossible to reliably read the overcurrent/overtemperature signal from the driver chip.

register/dc_brick/<UID>/velocity_reached
Request payload:
 
  • register -- bool
Response payload:
 
  • velocity -- int

A callback can be registered for this event by publishing to the .../register/dc_brick/<UID>/velocity_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/dc_brick/<UID>/velocity_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered whenever a set velocity is reached. For example: If a velocity of 0 is present, acceleration is set to 5000 and velocity to 10000, the register/dc_brick/<UID>/velocity_reached callback will be triggered after about 2 seconds, when the set velocity is actually reached.

Note

Since we can't get any feedback from the DC motor, this only works if the acceleration (see request/dc_brick/<UID>/set_acceleration) is set smaller or equal to the maximum acceleration of the motor. Otherwise the motor will lag behind the control value and the callback will be triggered too early.

register/dc_brick/<UID>/current_velocity
Request payload:
 
  • register -- bool
Response payload:
 
  • velocity -- int

A callback can be registered for this event by publishing to the .../register/dc_brick/<UID>/current_velocity[/<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/dc_brick/<UID>/current_velocity[/<SUFFIX>] topic for each registered suffix.

This callback is triggered with the period that is set by request/dc_brick/<UID>/set_current_velocity_period. The callback payload is the current velocity used by the motor.

The register/dc_brick/<UID>/current_velocity callback is only triggered after the set period if there is a change in the velocity.