/TFmini-I2C-ROS

A ROS package created from madewhatnow/TFmini-I2C-Python driver for I2C.

Primary LanguagePython

TFmini_plus_I2C_ROS

This is a repo from madewhatnow and configured for ROS framework.

Tested with TFmini-Plus-I2C on Raspberry Pi4. Some functions from the driver are not working for this model.

Install

cd ~/catkin_ws/src
git clone https://github.com/ikh-innovation/TFmini-I2C-ROS.git
cd ~/catkin_ws
catkin_make
rospack profile

Config

# Set BUS of I2C and device addresses.
i2cbus: 1

lidars:
  rear_lidar:
    device_address: 20

  front_lidar:
    device_address: 21

Run

roslaunch tfmini_plus_i2c_ros tfmini_plus.launch

Note: To configure each device with I2C, connect it to the raspberry and run the setAddress() from the TFmini_plus_I2C.py

Reading the Benewake TFmini-I2C LIDAR Module in Python

The TFmini I2C sensor module is termed a 'LIDAR' module, but really a fast TOF (time of flight) sensor based on a 850nm IR diode. The more common version of the sensor has a serial (UART) interface, but an I2C-only version exists. The TFmini-I2C module can read a distance between 30 cm to 1200 cm at up to 1000hz (standard: 100 Hz). The range and precision depends somewhat on lighting (shorter maximum range in bright sunlight) and reflectivity of the target (shorter maximum range for dark surfaces).

On a Raspberry Pi, I2c is often the more attractive option communication option, as it allows more sensors to be used in parallel. Unfortunately, as of May 2020, no python library or implementation to read the sensor via python was available online. This repository contains a compact proof of concept that allows reading the sensor values using the smbus2 library in Python, and will hopefully be expanded into a compact library.

The Benewake TFmini product line unfortunately (?) contains several models, with rather different characteristics and communication protocol. The script described here is ONLY intended for the TFmini I2c model (

TFmini

Only supports UART/serial

TFmini I2C

I2c enabled out of the box. The python code here is inteded for this model DigiKey Robotshop Sparkfun

TFmini-S

Newer version of the TFmini, supports both serial and I2C. Slightly different measurement range, lower power consumption.

TFmini plus

Newer version of the TFmini, supports both serial and I2C. Slightly different measurement range, lower power consumption.

Hardware setup

The TFmini-I2C module runs on 5V (with a peak current of 80mA!), so make sure the power supply can support the sensor. THe SCL and SDA lines run on 3.3V logic level, and can therefor be directly interfaced with a Raspberry Pi.

Potential concerns: the sensor might use clock stretching, which is broken on Raspberry Pis (supposedly fixed on the Raspberry Pi 4). Reducing the I2C bus speed, or creating a device tree overlay / software I2C bus should fix any problems.

See here for details:

https://learn.adafruit.com/circuitpython-on-raspberrypi-linux/i2c-clock-stretching https://github.com/fivdi/i2c-bus/blob/master/doc/raspberry-pi-software-i2c.md

Software setup

Use raspi-config to enable i2c, reboot. Install smbus2 via pip3

See here for details:

https://learn.adafruit.com/adafruits-raspberry-pi-lesson-4-gpio-setup/configuring-i2c

Basic usage

The TFmini_I2C.py file contains the necessary definitions and examples.

A sensor is initalized by passing the identifier for the I2C bus and the sensor address:

  Sensor0 = TFminiI2C(1, 0x10)
  Sensor1 = TFminiI2C(1, 0x11)

Reading the sensor is very simple and fast. The first command reads the full return of the sensor and returns four values:

  print(Sensor0.readAll())
  1. Trigger status (1 or 0)
  2. Distance value (standard in cm)
  3. Signal strength
  4. Ranging Mode (00, 03, 07 - indicateds short, medium or long range mode)

The second command performs the same read, but only returns the distance measurement as a single value. Standard unit is cm, but can be changed to mm, see further below.

  print(Sensor1.readDistance())

Changing settings

Once a sensor is intialized, settings can be adjusted:

  Sensor0.setUnit(0x00)
  Sensor0.setRange(0x07)

The first command changes the sensor output to millimeter (instead of centimeter), the second changes the standard automatic range settings (short, medium or long range) to a fixed range.

Similarly, both a 'soft' reset (to activate settings) or a 'reset to manufacturer default' can be called:

  Sensor1.reset()
  Sensor1.resetdefault()

The standard I2C address of the sensor is 0x10, but can be changed in the range from 0x10 to 0x78. The manual suggests that a soft reset is sufficient to activate the change, in my hands a power cycle is required. The address change is permanent, and survives both types of reset.

  Sensor0.setAddress(0x11)

Reading the sensor is fast. On a Raspberry Pi 4, the distance values for 3 different sensors are returned in around 4 milliseconds total.

Enjoy!