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Wearable Intertace for Teleoperation of Robot Arms - WITRA

 
[Update 3] IMU Razor 9DoF
Update #10113  |  19 Sep 2014
 

This update brings some information about the recently tested Razor 9DoF IMU. This IMU is sold, among other stores, by Sparkfun in the U.S.A. (https://www.sparkfun.com/products/10736). It features 3 sensors: an ITG-3200(MEMS triple-axis gyro), ADXL345 (triple-axis accelerometer), and HMC5883L (triple-axis magnetometer). Thus we have 9 Degrees of Freedom of measurement. The IMU has also a on-board ATmega328 for data processing. Thus, this is a very convenient IMU and is somehow a low-cost product. One can find a tutorial online on how to program and implement it on a project at https://github.com/ptrbrtz/razor-9dof-ahrs/wiki/Tutorial).

IMU Razor 9DoF

IMU Razor 9DoF

Besides, there is an available Firmware for the Razor 9DoF available at https://github.com/ptrbrtz/razor-9dof-ahrs through which is also possible to callibrate the sensors and select the way of outputting data. This firmware is very satisfactory and provides the user with a variety of programming and setup options such as callibrating sensor by sensor, choosing the data output between text and binary format. It also compensates the YAW reading in order to avoid a initial drifting, common in simpler IMUs. The Firmware is coded into Arduino language (since the onboard processor is an Arduino-like). However, there are also sample codes for Processing (animation on the screen), C++ (for data aquisition - only works on Linux, Unix and MacOSx operation systems) and Android (for communication wirelessly over Bluetooth with an Android device). Moreove, this IMU outputs data over a serial interface. Hence, it is also possible to hook up a Bluetooth modem to it in order to make the data transfer wireless. The modem we are using is a Bluetooth Mate Silver.

Bluetooth Mate Silver

Bluetooth Mate Silver

When not using the IMU wirelessly nor programming it, the board can be connected to the computer either using a FTDI cable (to connect to the computer’s USB port) or using a FTDI board. We decided to use a FTDI board. It’s important to say that there is a 5V and a 3.3V version of the FTDI cable/board. This IMU requires a 3.3V one.

FTDI Breakout

FTDI Breakout - 3.3V and 5V - Switchable

Furthermore, a LiPo battery is also used in order to power the whole thing. To make things easier, we chose a rechargeable LiPo battery and a LiPo battery USB chager. The whole setup is show below.

Wireless IMU Setup

Wireless Setup for IMU using Bluetooth

More information about the inertial sensor can be found at the links above. On the next post we'll show how to use Bluetooth with this IMU.

Comments, suggestions and opinions are always welcome! 

The WITRA Team.

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