Teensy 3.2 firmware for the Earth Rover

This package provides Teensy 3.2 firmware to control the Earth Rover via USB using the rosserial protocol. It currently provides a GPS module based on a MTK3339 sensor, a position encoder module based on two TLE4905L unipolar magnetic field switches and one or more magnets on the the drive shaft and an IMU module based on a BNO055 sensor and a servo module.

Modules

GPS Module

The GPS functionality is provided by an Adafruit Ultimate GPS Breakout based on a MTK3339 GPS sensor.

The rosserial GPS module provides one publisher:

• /mtk3339/nmea_sentence with the NMEA sentences published by the GPS sensor.

This publisher can be enabled or disabled by sending a true or false bool message to /mtk3339/enable. It is disabled by default.

The standard nmea_navsat_driver package provides a nmea_topic_driver node which translates the NMEA sentences to standard sensor_msgs/NavSatFix, geometry_msgs/TwistStamped and sensor_msgs/TimeReference ROS messages.

Position Encoder Module

The position encoder module is provided by two TLE4905L unipolar magnetic field switches and one or more magnets on the drive shaft. The TLE4905L requires a supply voltage of at least 3.8V, so it couldn't be powered by the Teensy's 3.3V supply. The input pin numbers are given as template parameters. The current firmware uses pins 5 and 6.

The rosserial position encoder module provides one publisher:

• /encoder/position with a 16 bit (overflowing) pulse counter.

This publisher can be enabled or disabled by sending a true or false bool message to /encoder/enable. It is disabled by default.

IMU Module

The IMU functionality is provided by an Adafruit 9-DOF Absolute Orientation IMU Fusion Breakout based on a Bosch BNO055 IMU sensor. The Teensy and the BNO055 breakout board communicate via I2C, so you'll have to connect the 3.3V, GND, SDA and SCL of the breakout board to your Teensy. Configure the Wire (or i2c_t3) interface before initializing the sensor. The current firmware uses the first I2C interface's SDA and SCL lines on pins 18 and 19.

The rosserial IMU module provides two publishers:

• /bno055/imu with the IMU's measurements (at 50 Hz) and
• /bno055/calib_status with the IMU's calibration status (at 1 Hz).

Both publishers can be enabled or disabled by sending a true or false bool message to /bno055/enable. They are disabled by default.

When the IMU is disabled while it is fully calibrated, the calibration offsets are stored in the Arduino's EEPROM memory. If stored offsets are available, they are restored after a reset.

This package also provides a imu_publisher_node node which translates the compact Bno055Measurements and Bno055CalibrationStatus messages to standard sensor_msgs/Imu ROS messages.

Servo module

The rosserial servo module provides three subscribers:

• /servo/control to set the servo's position relative (-1000 = minimum, 0 = center and +1000 = maximum) to the configured pulse width limits.
• /servo/control_raw to send absolute pulse widths (in µs) to the servo (for most servos, 1000µs = minimum and 2000µs = maximum).
• /servo/configure to configure the servo's initial, minimum, center and maximum pulse width.

The pin numbers are given as template parameters. The current firmware uses pins 20, 21, 22 and 23.

Dependencies

• ROS. I use Melodic Morenia on Ubuntu 18.04 LTS, but other versions might work too.
• rosserial_arduino.
• ros_teensy.
• Arduino IDE. I use version 1.8.8. Other versions might work too, but the one included in Ubuntu 18.04 LTS doesn't.
• Teensyduino. I use version 1.45.
• Teensy Loader.

Building

Include the packages in a ROS workspace. Both building (messages, firmware...) and uploading the firmware is done using catkin build (or catkin_make).

To build the package using catkin build, run:

• export arduino_location="/opt/arduino-1.8.8"
• . /opt/ros/melodic/setup.bash (or the version for your favourite shell)
• rm -rf build devel logs
• catkin build

Due to some internal details of rosserial_arduino's make_libraries.py script, building the package with catkin_make isn't as straightforward as I would like it to be. The problem is that to create our custom messages in the Arduino/Teensy ros_lib library, rosserial_arduino's make_libraries.py script needs to source the workspace's setup script, which isn't available until the build is finished. See [ros-drivers/rosserial#239] for more details. The most elegant workaround I found is to exclude the firmware from the default catkin_make target (remove the ALL from the rosserial_add_client_target command) and build it manually afterwards.

So, to build the package including the firmware for the Teensy 3.2 using catkin_make, run:

• export arduino_location="/opt/arduino-1.8.8"
• . /opt/ros/melodic/setup.bash (or the version for your favourite shell)
• rm -rf build devel
• catkin_make (to build everything except the firmware)
• . ./devel/setup.bash (or the version for your favourite shell)
• catkin_make earth_rover_firmware_firmware_teensy32_earth_rover_firmware_teensy32_Firmware (to build the firmware)
• teensy_loader_cli -mmcu=mk20dx256 -v -w ./build/earth_rover_firmware/firmware_teensy32/bin/earth_rover_firmware_teensy32.elf.hex (to upload the firmware to the Teensy 3.2)

Running

This package provides a earth_rover_firmware.launch launch file to start the rosserial interface node, enables all modules and starts the standard message (re)publishers.

License

MIT license, see LICENSE.md for details.