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WitMotionReader

This is a wrapper around the WitMotion SDK sample files for Linux that provides a way to build them into a library and them use them in a C program to open and read from a device. It presumes that the device has been configured and calibrated separately.

These instructions are specific to the GPS+inertial unit JY-GPSIMU with an internal antenna, whose device type is WTGAHRS2.

Configuring the device

Plug in the leads on the included USB adapter according to the TTL layout, which has black on GND, red on +5V, yellow on RXD and green on TXD.

There is a Windows program provided by WitMotion that can configure the baud rate and other settings on the device. There is a software link on their web page that points to a Google Drive that contains a WitMotion New Software.zip file with the program in it.

Follow the instructions in the Software Instructions Manual.pdf in that Google Drive to:

  • select the appropriate device type (WTGAHRS2) and then search for the device,
  • configure the baud rate on the device to be 230400,
  • configure the bandwidth to be 188 Hz,
  • configure the output rate to be 100 Hz, and
  • configure the channels to be read so that they include those needed (Time, Acceleration, Velocity, Angle, Location, PDOP, and Positioning Accuracy).

Calibrating the device

Follow the instructions in the Software Instructions Manual.pdf in that Google Drive to:

  • Calibrate the accelerometer, and
  • Calibrate the magnetic field.

Setting permissions on Linux

Plug the device into a USB port on the Linux system. This should produce a virtual TTY device, perhaps /dev/ttyS0. Permissions must be set on the device for the current user: sudo chmod 666 /dev/ttyS0 (adjusting the device name as needed).

Building this example software

The source code for this project is available on Github. One way to download and build it is as follows:

mkdir -p ~/src
cd ~/src
git clone --recursive https://github.com/ReliaSolve/WitMotionReader.git
mkdir -p ~/build/WitMotionReader
cd ~/build/WitMotionReader
cmake ~/src/WitMotionReader
make

Running

The make during build will generate a program named witExample that can be run with the name of the virtual serial port to use. For example, ./witExample /dev/ttyS0 (adjusting the device name as needed). This program should auto-detect the baud rate on the device and then start printing the acceleration, gyro rotation rate, angle of orientation, and magnetometer readings. Press ^C to quit the program.

It will also generate a program named example from example.c that is both simpler and has a more general list of data values. It is also more heavily commented. It is intended to be used as an example for developing a driver that uses this device.

Additional data fields:

There is a [protocol description document] (https://drive.google.com/file/d/1xrfK9bAEncgFQYjvT_c6vwSEH0ZhzaUZ/view?usp=drive_link) that describes the formats and how to convert the registers into values.