EXEL EXLs3 User manual

EXLs3 rev09-051114

EXLs3

Miniature Wireless

Inertial Measurement Unit

USER GUIDE

(FIRMWARE REV.6.26)

Table of contents



1. GENERAL DESCRIPTION ....................................................3



2. FEATURES ............................................................................3



3. HARDWARE OVERVIEW......................................................4



4. INTERNAL BLOCK DIAGRAM .............................................6



5. REFERENCE SYSTEM..........................................................7



6. MEASUREMENT UNITS........................................................8



7. BLUETOOTH SETUP............................................................9

8. COMUNICATION PROTOCOL............................................13

8.1. BASIC COMMANDS............................................................13

8.2. PACKET DATA TYPES........................................................13

8.3. CONFIGURATION COMMANDS............................................16

8.4. CONFIGURATION REGISTERS.............................................16

8.5. CONFIGURATION PARAMETER ACCESS..............................19

8.6. REAL TIME CLOCK CONFIGURATION...................................21

8.7. OTHER COMMANDS...........................................................22

APPENDIX A. FIRMWARE UPDATE.....................................23

LEGACY FUNCTIONS.............................................................26

EXLs3

Miniature Wireless Inertial Measurement Unit

1. GENERAL DESCRIPTION

The EXLs3 is a miniaturized electronic device with the function of real-time Inertial Measurement Unit

(IMU).

It features a complete MEMS sensor set, which is composed of a tri-axial accelerometer, gyroscope

and compass, a 32-bit Cortex microprocessor for data processing and a Bluetooth radio to send real-

time data.

The unit can be used for real-time motion measurement and transmission in particular in the medical field

as a wearable device for biomechanical analysis, such as posture assessment, rehabilitation, gait

monitoring, joints’ functionality analysis, activity monitoring, etc.

The Bluetooth™ radio allows easy interfacing to a wide range of devices (PC, Tablets, Smartphones)

without the need of additional hardware so that data can be transmitted wirelessly up to 10 meters.

The unit is also equipped with an embedded 1 GB flash drive which allows data logging to CSV files

and USB interface for file transfer.

The on board 32-bit CPU provide algorithms for orientation estimation with Kalman filtering in order to

give high quality measurement.

The integrated rechargeable Litium battery allows continuous data acquisition and streaming up to 3

hours and can be recharged by means of a dedicated docking station.

2. FEATURES

Module size 54 mm x 33 mm x 14 mm

Module weight 22 g

32-bit MCU, Cortex-M3 @72 MHz

3-axis accelerometer with selectable full-scale range (±2 / ±4 / ±8 / ±16 g).

3-axis gyroscope with selectable full-scale range (±250 / ±500 / ±1000 / ±2000 dps)

3-axis magnetometer

Orientation estimation with Kalman filtering and quaternion output.

Sampling rate up to 200 Hz for raw data and 100 Hz for orientation data.

Various data packet format available

Bluetooth™ 2.1 class 1.

Up to 7 nodes at the same time can stream data to the same host.

1GB Flash Memory (USB Mass Storage) for data storage

Docking station with micro-USB connector for battery recharging and log-file downloading.

Battery operating time 3h

Firmware upgradable by means of bluetooth connection.

3. HARDWARE OVERVIEW

On the front side of the IMU the ON/OFF button and an indicator LED are located.

In order to switch-on the device, press shortly the button. The LED lights green.

To switch-off the IMU press and hold the button for two seconds, until the LED turns-off.

In addition, the IMU turns-off automatically after 10 minute of inactivity.

When the battery reaches a low voltage the LED starts blinking red.

On the back side 4 golden contacts are present in order to allow communication with the docking station

for battery recharging and data download.

The Docking-station allows the sensor to be interfaced to a PC via USB cable, for battery recharging

and data-log file transfer.

The IMU must be properly placed in the docking station as shown in the above picture.

For battery recharging is alternatively possible to connect the docking station to a standard 5V power

supply equipped with micro-USB connector.

The current required to recharge the battery is 250 mA.

When the battery is being charged the EXLs3’s indicator LED turns red.

When the battery is fully charged the LED turns green.

By connecting the docking-station to a PC it is possible to access the IMU’s internal storage flash disk, in

order to retrieve data-log files.

The Multiple Docking-Station allows more units to be recharged at the same time. It also acts as USB

hub which allows more units to be seen as multiple distinct flash disks where log files can be found.

The multiple docking-station must be used with the provided Power Supply Adapter, otherwise neither

battery recharging nor USB hub will work.

The IMU is provided with a special holder which allows easy fixing to a Velcro-strap or similar.

The IMU must be placed as shown in the following picture, by sliding it in the holder gently until the

body hooks in the retainer, making sure the holder’s lateral rails fit in the respective sensor’s slots.

In case of gait analysis the holder can be used to hook the IMU to shoes-laces, as shown in the

following picture.

4. INTERNAL BLOCK DIAGRAM

The following picture shows in a simplified form the internal logic of the EXLs3 unit.

The task of the unit is to measure in real-time the linear acceleration and the angular velocity at which

the unit itself is subjected (inertial measurements).

The unit can at the same time measure the magnitude of the surrounding magnetic field.

All measurements are performed by tri-axial sensors, so both magnitude and vector direction are

acquired.

After the compensation of sensor’s raw data (i.e. offset and gain error removal), data and are processed

in order to calculate the orientation of the unit related to a earth reference frame in real-time.

Compensated inertial data together with Orientation data are packed and sent wirelessly to the host PC a

the desired sampling rate.

The produced stream can also be saved in the internal flash drive, as standard CSV file, in order to be

retrieved afterwards via USB connection for off-line post-processing and/or analysis.

3-axis

Digital

Accelerometer

3-axis

Digital

Gyroscope

3-axis

Digital

Magnetometer

comp

ORIENTATION ESTIMATION

Linear Acceleration

(m/s²)

Angular Speed

(rad/s)

Earth Magnetic

Field (µT)

RAW DATA COMPENSATED DATA

DATA

PAC KING

AND

TIME-

STAMPING

BLUETOOTH

RADIO

DATA-LOG

ON INTERNAL

DRIVE

(CSV FILE)

HOST PC

5. REFERENCE SYSTEM

All raw inertial measurements (linear accelerations, angular velocity and earth magnetic field

provided by the unit are referred to the reference system shown below (body frame).

The orientation of the unit in the space is referred to an earth-bound frame where:

Xis pointing NORTH

Yis pointing WEST

Zis pointing UPWARDS

The orientation of the sensor is given by a quaternion (q0,q1,q2,q3) representing the rotation of the

unit’s body frame with respect to the earth frame.

Thus when the X axis of the sensor is pointing NORTH and Y axis is pointing WEST the output is the

Identity Quaternion (1,0,0,0).

6. MEASUREMENT UNITS

Main data returned in real-time by the EXLs3 to the host system are:

Acceleration (AccX, AccX, AccZ)

Angular Velocity (GyrX, GyrY, GyrZ)

Magnetic Field (MagX, MagY, MagZ)

Orientation (Q0, Q1, Q2, Q3)

For the Acceleration and the Angular Velocity you can chose among several full-scale ranges in order to

best fit the specific application requirement.

All data are sent in binary form, so they require conversion to be expressed in standard measurement

units.

ACCELERATION

a [m/sec2] = Ka 𝐴𝑐𝑐

32768

SELECTED

FULL-SCALE

RANGE

±2 g

2 x g (19.613 m/sec2)

±4 g

4 x g (39.227 m/sec2)

±8 g

8 x g (78.45 m/sec2 )

±16 g

16 x g (156.91 m/sec2 )

This formula must be applied to each component (AccX, AccY and AccZ) of the acceleration.

ANGULAR VELOCITY

ω[degree/sec] = Kg 𝐺𝑦𝑟

32768

SELECTED

FULL-SCALE

RANGE

±250 dps

250 dps

±500 dps

500 dps

±1000 dps

1000 dps

±2000 dps

2000 dps

This formula must be applied to each component (GyrX, GyrYand GyrZ) of the angular velocity.

MAGNETIC FIELD

B[uT] = Km 𝑀𝑎𝑔

FULL-SCALE

RANGE

±1200 dps

0.007629 uT

This formula must be applied to each component (MagX, MagYand MagZ) of the angular velocity.

ORIENTATION

The orientation of the EXLs3 in the space is represented by a unit quaternion (q0, q1 , q2, q3)

representing the rotation of the unit’s body frame with respect to the earth frame.

The quaternion’s components returned by the EXLs3 are normalized so that the unity is represented by

the value 16384.So the following formula should be applied:

qn= 𝑄𝑛

16384 n = 0,1,2 and 3

The rotation of the body-frame is identified by an axis of rotation A and an angle of rotation αaround that

axis:

q0= cos(α / 2)

q1= Axsin(α / 2)

q2= Aysin(α / 2)

q3= Azsin(α / 2)

EXAMPLES:

A rotation of +90 degrees around the Z axis (0,0,1) results:

q0= cos(90 / 2) = 0.7071

q1= 0 sin(90 / 2) = 0

q2= 0 sin(90 / 2) = 0

q3= 1 sin(90 / 2) = 0.7071

A rotation of -90 degrees around the Y axis (0,1,0) results:

q0= cos(-90 / 2) = 0.7071

q1= 0 sin(-90 / 2) = 0

q2= 1 sin(-90 / 2) = -0.7071

q3= 0 sin-(90 / 2) = 0

The Identity Quaternion (1,0,0,0) indicates the unit’s body frame (X-Y-Z) is aligned with the North-West-Up earth-frame.

7. BLUETOOTH SETUP

The communication with the unit is done via bluetooth SPP connection, so you should have a Bluetooth

2.1 internal card or USB Bluetooth dongle properly installed on your host machine.

After, you must pair each EXLs3 with the host by going to View Devices and Printers (under Windows 7)

and clicking on Add a device. Note your EXLs3 device(s) must be switched-on in order to be

discoverable by the host.

After a few seconds (up to 15) you should se a list of the available EXLs3 devices and you can select

the one you want to pair.

After a few seconds (up to 15) you should se a list of the available EXLs3 devices and you can select

the one you want to pair.

Note: for FW rev 6.26+ the EXLs3 is seen as generic Bluetooth device instead of bluetooth headset

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