tfmpi2c-budryerson 0.0.5

Added address parameter interpretation

tfmpi2c

A Python module for the Benewake TFMini-Plus Lidar sensor in I2C mode

The TFMini-Plus is largely compatible with the TFMini-S and therefore that device is able to use this module. One difference is that upon command to change communication mode, such as SET_I2C_MODE or SET_SERIAL_MODE, the TFMini-Plus switches mode immediately, whereas the TFMini-S requires a subsequent SAVE_SETTING command before the change takes place. This module is not compatible with the TFMini, which is an entirely different product with its own command set and data structure.

From hardware v1.3.5 and firmware v1.9.0 and above, the TFMini-Plus interface can be configured in either UART (Serial) or I2C (two-wire) communication mode

Internally, the device samples at about 4KHz. It presents frames of data to the interface at a programmable rate from 0 up to about 10KHz. The default data-frame rate is 100Hz. "Standard" data-frame rates are: 0, 1, 2, 5, 10, 20, 25, 50, 100, 125, 200, 250, 500, and 1000Hz. Single data-frames can be obtained by setting the frame rate to 0 and sending a TRIGGER_DETECTION command.

Three measurement values are returned by the device:
  ●  dist - Distance in centimeters or millimeters. Range: 0 - 1200/12000
  ●  flux - Strength, voltage or quality of signal in arbitrary units. Range: -1, 0 - 32767
  ●  temp - Internal temperature of the device. Range: -25°C to 125°C

Installed with the module is a tests folder that contains an example python script, tfmpi2c_test.py.

All the code in this module and the example script is richly commented to assist with understanding and problem solving. Feel free to steal whatever may be helpful to you.

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I2C mode operation

This module supports only the I2CT (two-wire) communication interface. It is up to the user to ensure that the device is in that interface mode.

To configure the device for I2C communication, a command must be sent using the UART interface. This reconfiguration should be made prior to the device's service installation, either by the serial GUI test application and command code supplied by the manufacturer, or by using the example script included with the tfmplus python module to send the SET_I2C_MODE command.

The device will remain in I2C mode after power has been removed and restored. The only way to return to serial mode is with the SET_SERIAL_MODE command. Even a RESTORE_FACTORY_SETTINGS command will NOT restore the device to its default, UART communication interface mode.

The TFMini-Plus functions as an I2C slave device and the default address is 0x10 (16 Decimal) but is programmable with the SET_I2C_ADDRESS command and a parameter in the range of 1 to 127. The new setting will take effect immediately and permanently without a SAVE_SETTINGS command, however the RESTORE_FACTORY_SETTINGS command will restore the default address. The I2C address can be set while still in serial communication mode or, if in I2C mode, an example script included in the TFMini-Plus-I2C module can be used to test and change the address.

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Three tfmpi2c module functions

The three module functions are defined in the main module file, TFMPlus.py. Status code, command and parameter variables are declared in the extension file, TFMPlus_h.py.

begin( port, address) passes the I2C port number and device address to the module, tries to open the port, performs a quick write operation and returns a boolean value indicating successful completion.

getData() commands the device to transmit a data-frame, gets the data-frame and extracts the three measurement data values. It sets the error status byte code and returns a boolean value indicating function 'pass/fail'.

sendCommand( cmnd, param) sends a coded command and a parameter to the device. It sets the status error code byte and returns a boolean 'pass/fail' value. A proper command (cmnd) must be selected from the module's list of twenty defined commands. A parameter (param) may be chosen from the module's list of defined parameters (such as data-frame rate) or entered directly (such as device I2C address). An erroneous parameter can block communication and there is no external means of resetting the device to factory defaults.

Any change of device settings must be followed by a SAVE_SETTINGS command or else the modified values may be lost when power is removed. SYSTEM_RESET and RESTORE_FACTORY_SETTINGS do not require a SAVE_SETTINGS command.

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Using the I/O modes of the device

The so-called I/O modes are not supported in this module. Please do not attempt to use any I/O commands that you may find to be defined in this module's list of defined commands or parameters.

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Finally

Benewake is not very forthcoming about the internals, but they did share this:

Some commands that modify internal parameters are processed within 1ms. Some commands require the MCU to communicate with other chips may take several ms. And some commands, such as saving configuration and restoring the factory settings need to erase the FLASH of the MCU, which may take several hundred ms.

And also:

1- the measuring frequency of the module should be 2.5 times larger than the IIC reading frequency.
2- the iic reading frequency should not exceed 100hz

Since the Data-Frame Rate is limited to 1000Hz, this condition implies a 400Hz data sampling limit in I2C mode. Benewake says sampling should not exceed 100Hz. They don't say why; but you might keep that limitation in mind when you consider using the I2C interface.