Software / API Bindings / MQTT / API Reference and Examples / Bricklets / DC Bricklet 2.0

MQTT - DC Bricklet 2.0¶

This is the description of the MQTT API bindings for the DC Bricklet 2.0. General information and technical specifications for the DC Bricklet 2.0 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)

# Change XYZ to the UID of your DC Bricklet 2.0

setup:
    publish '{"mode": "drive_coast"}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_drive_mode

    publish '{"frequency": 10000}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_pwm_frequency # Use PWM frequency of 10 kHz

    publish '{"acceleration": 4096, "deceleration": 16384}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_motion # Slow acceleration (12.5 %/s), fast decceleration (50 %/s) for stopping

    publish '{"velocity": 32767}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_velocity # Full speed forward (100 %)

    publish '{"enabled": true}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_enabled # Enable motor power

cleanup:
    # If you are done, run this to clean up
    publish '{"velocity": 0}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_velocity # Stop motor before disabling motor power

    wait for 2s # Wait for motor to actually stop: velocity (100 %) / decceleration (50 %/s) = 2 s

    publish '{"enabled": false}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_enabled # Disable motor power

Callback¶

Download (example-callback.txt)

# Change XYZ to the UID of your DC Bricklet 2.0

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": 4096, "deceleration": 16384}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_motion # Slow acceleration (12.5 %/s), fast decceleration (50 %/s) for stopping

    publish '{"velocity": 32767}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_velocity # Full speed forward (100 %)

    # Use velocity reached callback to swing back and forth
    # between full speed forward and full speed backward
    subscribe to tinkerforge/callback/dc_v2_bricklet/XYZ/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_v2_bricklet/XYZ/set_velocity
            elseif velocity == -32767
                print "Velocity: Full speed backward, now turning forward"
                publish '{"velocity": 32767}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_velocity
            else
                print "Error"
            endif
        endif
    endsubscribe

    publish '{"register": true}' to tinkerforge/register/dc_v2_bricklet/XYZ/velocity_reached # Register velocity_reached callback

    # Enable motor power
    publish '{"enabled": true}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_enabled

cleanup:
    # If you are done, run this to clean up
    publish '{"velocity": 0}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_velocity # Stop motor before disabling motor power

    wait for 2s # Wait for motor to actually stop: velocity (100 %) / decceleration (50 %/s) = 2 s

    publish '{"enabled": false}' to tinkerforge/request/dc_v2_bricklet/XYZ/set_enabled # Disable motor power

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/dc_v2_bricklet/<UID>/set_enabled¶

Request:	enabled – Type: bool
Response:	no response

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

request/dc_v2_bricklet/<UID>/get_enabled¶

Request:	empty payload
Response:	enabled – Type: bool, Default: false

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

request/dc_v2_bricklet/<UID>/set_velocity¶

Request:	velocity – Type: int, Unit: 100/32767 %, Range: [-2¹⁵ + 1 to 2¹⁵ - 1], Default: 0
Response:	no response

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_v2_bricklet/<UID>/set_motion), 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_v2_bricklet/<UID>/set_pwm_frequency.

request/dc_v2_bricklet/<UID>/get_velocity¶

Request:	empty payload
Response:	velocity – Type: int, Unit: 100/32767 %, Range: [-2¹⁵ + 1 to 2¹⁵ - 1], Default: 0

Returns the velocity as set by request/dc_v2_bricklet/<UID>/set_velocity.

request/dc_v2_bricklet/<UID>/get_current_velocity¶

Request:	empty payload
Response:	velocity – Type: int, Unit: 100/32767 %, Range: [-2¹⁵ + 1 to 2¹⁵ - 1], Default: 0

Returns the current velocity of the motor. This value is different from request/dc_v2_bricklet/<UID>/get_velocity whenever the motor is currently accelerating to a goal set by request/dc_v2_bricklet/<UID>/set_velocity.

request/dc_v2_bricklet/<UID>/set_motion¶

Request:	acceleration – Type: int, Unit: 100/32767 %/s, Range: [0 to 2¹⁶ - 1], Default: 10000 deceleration – Type: int, Unit: 100/32767 %/s, Range: [0 to 2¹⁶ - 1], Default: 10000
Response:	no response

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

request/dc_v2_bricklet/<UID>/get_motion¶

Request:	empty payload
Response:	acceleration – Type: int, Unit: 100/32767 %/s, Range: [0 to 2¹⁶ - 1], Default: 10000 deceleration – Type: int, Unit: 100/32767 %/s, Range: [0 to 2¹⁶ - 1], Default: 10000

Returns the acceleration/deceleration as set by request/dc_v2_bricklet/<UID>/set_motion.

request/dc_v2_bricklet/<UID>/full_brake¶

Request:	empty payload
Response:	no response

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_v2_bricklet/<UID>/set_velocity with 0 if you just want to stop the motor.

request/dc_v2_bricklet/<UID>/get_pwm_frequency¶

Request:	empty payload
Response:	frequency – Type: int, Unit: 1 Hz, Range: [1 to 20000], Default: 15000

Returns the PWM frequency as set by request/dc_v2_bricklet/<UID>/set_pwm_frequency.

request/dc_v2_bricklet/<UID>/get_power_statistics¶

Request:	empty payload
Response:	voltage – Type: int, Unit: 1 mV, Range: [0 to 2¹⁶ - 1] current – Type: int, Unit: 1 mA, Range: [0 to 2¹⁶ - 1]

Returns input voltage and current usage of the driver.

Advanced Functions¶

request/dc_v2_bricklet/<UID>/set_drive_mode¶

Request:	mode – Type: int, Range: See symbols, Default: 0
Response:	no response

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 following symbols are available for this function:

For mode:

"drive_brake" = 0
"drive_coast" = 1

request/dc_v2_bricklet/<UID>/get_drive_mode¶

Request:	empty payload
Response:	mode – Type: int, Range: See symbols, Default: 0

Returns the drive mode, as set by request/dc_v2_bricklet/<UID>/set_drive_mode.

The following symbols are available for this function:

For mode:

"drive_brake" = 0
"drive_coast" = 1

request/dc_v2_bricklet/<UID>/set_pwm_frequency¶

Request:	frequency – Type: int, Unit: 1 Hz, Range: [1 to 20000], Default: 15000
Response:	no response

Sets the frequency of the PWM with which the motor is driven. 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.

request/dc_v2_bricklet/<UID>/set_error_led_config¶

Request:	config – Type: int, Range: See symbols, Default: 3
Response:	no response

Configures the error LED to be either turned off, turned on, blink in heartbeat mode or show an error.

If the LED is configured to show errors it has three different states:

Off: No error present.
1s interval blinking: Input voltage too low (below 6V).
250ms interval blinking: Overtemperature or overcurrent.

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_error" = 3

request/dc_v2_bricklet/<UID>/get_error_led_config¶

Request:	empty payload
Response:	config – Type: int, Range: See symbols, Default: 3

Returns the LED configuration as set by request/dc_v2_bricklet/<UID>/set_error_led_config

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_error" = 3

request/dc_v2_bricklet/<UID>/get_spitfp_error_count¶

Request:	empty payload
Response:	error_count_ack_checksum – Type: int, Range: [0 to 2³² - 1] error_count_message_checksum – Type: int, Range: [0 to 2³² - 1] error_count_frame – Type: int, Range: [0 to 2³² - 1] error_count_overflow – Type: int, Range: [0 to 2³² - 1]

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 Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.

request/dc_v2_bricklet/<UID>/set_status_led_config¶

Request:	config – Type: int, Range: See symbols, Default: 3
Response:	no response

Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.

You can also turn the LED permanently on/off or show a heartbeat.

If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_status" = 3

request/dc_v2_bricklet/<UID>/get_status_led_config¶

Request:	empty payload
Response:	config – Type: int, Range: See symbols, Default: 3

Returns the configuration as set by request/dc_v2_bricklet/<UID>/set_status_led_config

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_status" = 3

request/dc_v2_bricklet/<UID>/get_chip_temperature¶

Request:	empty payload
Response:	temperature – Type: int, Unit: 1 °C, Range: [-2¹⁵ to 2¹⁵ - 1]

Returns the temperature 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 bad accuracy. Practically it is only useful as an indicator for temperature changes.

request/dc_v2_bricklet/<UID>/reset¶

Request:	empty payload
Response:	no response

Calling this function will reset the Bricklet. All configurations will be lost.

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

request/dc_v2_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", "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). A Bricklet connected to an Isolator Bricklet is always at 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 DC 2.0's name in a human readable form.

Callback Configuration Functions¶

request/dc_v2_bricklet/<UID>/set_emergency_shutdown_callback_configuration¶

Request:	enabled – Type: bool, Default: false
Response:	no response

Enable/Disable register/dc_v2_bricklet/<UID>/emergency_shutdown callback.

request/dc_v2_bricklet/<UID>/get_emergency_shutdown_callback_configuration¶

Request:	empty payload
Response:	enabled – Type: bool, Default: true

Returns the callback configuration as set by request/dc_v2_bricklet/<UID>/set_emergency_shutdown_callback_configuration.

request/dc_v2_bricklet/<UID>/set_velocity_reached_callback_configuration¶

Request:	enabled – Type: bool, Default: false
Response:	no response

Enable/Disable register/dc_v2_bricklet/<UID>/velocity_reached callback.

request/dc_v2_bricklet/<UID>/get_velocity_reached_callback_configuration¶

Request:	empty payload
Response:	enabled – Type: bool, Default: false

Returns the callback configuration as set by request/dc_v2_bricklet/<UID>/set_velocity_reached_callback_configuration.

request/dc_v2_bricklet/<UID>/set_current_velocity_callback_configuration¶

Request:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false
Response:	no response

The period is the period with which the register/dc_v2_bricklet/<UID>/current_velocity callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

request/dc_v2_bricklet/<UID>/get_current_velocity_callback_configuration¶

Request:	empty payload
Response:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false

Returns the callback configuration as set by request/dc_v2_bricklet/<UID>/set_current_velocity_callback_configuration.

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_v2_bricklet/<UID>/emergency_shutdown¶

Register Request:	register – Type: bool
Callback Response:	empty payload

A callback can be registered for this event by publishing to the .../register/dc_v2_bricklet/<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_v2_bricklet/<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_v2_bricklet/<UID>/set_enabled has to be called to drive the motor again.

Note

This callback only works in Drive/Brake mode (see request/dc_v2_bricklet/<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_v2_bricklet/<UID>/velocity_reached¶

Register Request:	register – Type: bool
Callback Response:	velocity – Type: int, Unit: 100/32767 %, Range: [-2¹⁵ + 1 to 2¹⁵ - 1]

A callback can be registered for this event by publishing to the .../register/dc_v2_bricklet/<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_v2_bricklet/<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_v2_bricklet/<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_v2_bricklet/<UID>/set_motion) 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_v2_bricklet/<UID>/current_velocity¶

Register Request:	register – Type: bool
Callback Response:	velocity – Type: int, Unit: 100/32767 %, Range: [-2¹⁵ + 1 to 2¹⁵ - 1]

A callback can be registered for this event by publishing to the .../register/dc_v2_bricklet/<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_v2_bricklet/<UID>/current_velocity[/<SUFFIX>] topic for each registered suffix.

This callback is triggered with the period that is set by request/dc_v2_bricklet/<UID>/set_current_velocity_callback_configuration. The callback payload is the current velocity used by the motor.

The register/dc_v2_bricklet/<UID>/current_velocity callback is only triggered after the set period if there is a change in the velocity.

Internal Functions¶

Internal functions are used for maintenance tasks such as flashing a new firmware of changing the UID of a Bricklet. These task should be performed using Brick Viewer instead of using the internal functions directly.

request/dc_v2_bricklet/<UID>/set_bootloader_mode¶

Request:	mode – Type: int, Range: See symbols
Response:	status – Type: int, Range: See symbols

Sets the bootloader mode and returns the status after the requested mode change was instigated.

You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

The following symbols are available for this function:

For mode:

"bootloader" = 0
"firmware" = 1
"bootloader_wait_for_reboot" = 2
"firmware_wait_for_reboot" = 3
"firmware_wait_for_erase_and_reboot" = 4

For status:

"ok" = 0
"invalid_mode" = 1
"no_change" = 2
"entry_function_not_present" = 3
"device_identifier_incorrect" = 4
"crc_mismatch" = 5

request/dc_v2_bricklet/<UID>/get_bootloader_mode¶

Request:	empty payload
Response:	mode – Type: int, Range: See symbols

Returns the current bootloader mode, see request/dc_v2_bricklet/<UID>/set_bootloader_mode.

The following symbols are available for this function:

For mode:

"bootloader" = 0
"firmware" = 1
"bootloader_wait_for_reboot" = 2
"firmware_wait_for_reboot" = 3
"firmware_wait_for_erase_and_reboot" = 4

request/dc_v2_bricklet/<UID>/set_write_firmware_pointer¶

Request:	pointer – Type: int, Unit: 1 B, Range: [0 to 2³² - 1]
Response:	no response

Sets the firmware pointer for request/dc_v2_bricklet/<UID>/write_firmware. The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/dc_v2_bricklet/<UID>/write_firmware¶

Request:	data – Type: [int, ...], Length: 64, Range: [0 to 255]
Response:	status – Type: int, Range: [0 to 255]

Writes 64 Bytes of firmware at the position as written by request/dc_v2_bricklet/<UID>/set_write_firmware_pointer before. The firmware is written to flash every 4 chunks.

You can only write firmware in bootloader mode.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/dc_v2_bricklet/<UID>/write_uid¶

Request:	uid – Type: int, Range: [0 to 2³² - 1]
Response:	no response

Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.

We recommend that you use Brick Viewer to change the UID.

request/dc_v2_bricklet/<UID>/read_uid¶

Request:	empty payload
Response:	uid – Type: int, Range: [0 to 2³² - 1]

Returns the current UID as an integer. Encode as Base58 to get the usual string version.