here in pdf form (Rev New, April 2014)
Contents
1. www gcdataconcepts com 1 Features 3 axis 16g accelerometer Operates from internal rechargeable lithium polymer battery 16 bit resolution User selectable sample rate of 12 25 50 100 200 400 800 Hertz Finite Impulse Response filter Accurate time stamped data using Real Time Clock RTC Convenient on off button Data recorded to a removable microSD card 8GB included e Easily readable comma separated text data files e Data transfer compatible with Windows or Linux via Universal Serial Bus USB interface no special software e System appears as USB Mass Storage Device to Windows and Linux OS s LED indicator lights for system status Weighs 1 30z 48g Gulf Coast Data Concepts USB Accelerometer Model X16 4 2 Applications The X16 4 is applicable to e Monitoring human motor activity or actigraphy such as exercise intensity or sleeping disorders e Automotive performance monitoring e Educational purposes 3 Description The USB Accelerometer model X16 4 data logger uses a low noise digital accelerometer sensor precise time stamped data logging microSD memory storage real time data access and USB connectivity Acceleration is collected in X Y and Z axes and stored at a user selectable rate of up to 800hz When connected via the USB to a personal computer the X16 4 appears as a standard mass storage device containing the comma delimited data files and user setup files The internal lithtum2. 50 100 200 Sets the rate at which data is collected and recorded 400 800 to the microSD card starttime and stoptime See section 3 2 4 8 a Defines when to start and stop recording stoponvusb Stops data logging if 5v USB power is present see section 3 2 4 9 statusindicators Normal High LED status indicators can be activated with normal Off brightness Normal activated with high brightness High or completely deactivated Off 3 2 4 1 deadband deadband defines the minimum difference between recorded sensor readings A new sample from the accelerometer sensor must exceed the previous recorded reading before the microcontroller records the data The deadband setting is expressed in counts units and is applied to the output of each axis There are 2048 counts per g The deadband value can be set to an integer between 0 and 32767 The deadband function is an effective way to reduce the amount of data collected by defining the granularity of the data The deadband functions as a event threshold limit when used in conjunction with the dwell feature Figure 5 illustrates the deadband feature filtering out small changes in acceleration from the recorded data Only when the deadband limit is exceeded will a new data sample be pushed to the file Note that this feature will result in samples with inconsistent time periods Therefore the data sets should be re sampled to establish uniform time periods J
3. and microSDHC type cards The X16 4 functions as a Mass Storage Device to computer operating systems when transferring data to and from the microSD memory card The Mass Storage Device interface is supported by all desktop operating systems and special device drivers are not required Tablet computers may not recognize the X16 4 due to USB device limitations set by the tablet manufacturer The logger needs only the config txt file to operate The X16 4 will use default configuration settings if the config txt is not present The config txt and time txt files must occur in the root directory see section 3 2 4 and section 3 2 6 The X16 4 will create a folder called GCDC if not already present to place the data files see section 3 2 5 Interrupting the power to the logger can result in corruption of the microSD card For example removing the logger from the USB port during file transfers to the PC Reformat the card if it becomes corrupted FAT32 file structure If data transfers to from the card become slow consider formatting the card using SD Card Formatter software provided by the SD Association www sdcard org June 2014 Rev New 13 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 3 3 Mechanical The X16 4 electronics are enclosed in a three part semi transparent blue plastic enclosure The top and bottom enclosure components and the printed circuit board are secured together with a 0 75
4. long 6 32 screw and nut A slip on cap protects the USB connector The X16 4 weighs 1 30z 48g The X16 4 is small and very light weight so attachment methods do not need to be substantial Double sided tape a spot of cyanoacrylate glue contact cement zip ties magnetic base or adhesive putty are example methods of attachment These methods do not cause adverse signal attenuation considering the relatively low frequency bandwidth of the X16 4 logger Command Poster Adhesive strips by 3M offer excellent temporary attachment of the logger to most surfaces 3 3 1 Dimensions Figure 12 Enclosure Dimensions 3 3 2 Assembly 0 75 Length 6 32 Machine Screw PCB Enclosure Top PCB Enclosure Cap On Off Button 6 32 Hex eo Hho aaa Figure 13 Exploded View of the X16 4 June 2014 Rev New 14 of 16 www gcdataconcepts com 4 Software USB Accelerometer Model X16 4 The X16 4 records data to comma delimited text files and uses text based files for configuration settings Therefore no special software is required to utilize the X16 4 For data analysis Gulf Coast Data Concepts recommends using a commercial or open source mathematics package such as MatLab Microsoft Excel OpenOffice Calc Octave R or similar applications 5 Troubleshooting Problem Resolution I press the on off button but the logger does not appear to activate and no LEDs
5. type accelerometer sensor similar to those used in cellphones laptops hard drives and other consumer electronics The sensor streams data at a selected rate based the on timing of a clock internal to the sensor This sensor clock isn t perfect and the precision and drift are undefined For example a selected sample rate of 50 Hz may actually occur at 52 Hz The X16 4 incorporates a precise real time clock to independently time stamp the sensor data and ensure that accurate timing is recorded to the data file Therefore always reference the time stamps to determine the actual sample rate June 2014 Rev New 8 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 3 2 4 8 starttime and stoptime The X16 4 starts and stops data recording based on the times defined using the starttime and stoptime tags The times must be in MM HH DD 24 hr format with the three entries separated by a space Entries marked with operate as a wild card The X16 4 continues to record after the start time unless defined otherwise by the stoptime tag Note that the configuration option does not include the month Example timing configurations Example 1 On the 15 day start recording at 12 30pm and stop recording at 6 00pm starttime 30 12 15 stoptime 00 18 15 Example 2 Start recording at the beginning of every hour and stop recording 45 minutes later starttime 00 stoptime 45 3 2 4 9 stoponvusb T
6. 2 26 30 pm June 16 2014 June 2014 Rev New 12 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 The time file method of setting the RTC does not require special communication drivers so it can be implemented using a simple text editor Direct initialization of the RTC is possible but requires specific device drivers and software from Gulf Coast Data Concepts The RTC maintains 5ppm accuracy 40 C to 85 C which means that it will drift accuracy about 1 second every 2 days The RTC is powered by the battery at all times even when the logger is off 2014 06 16 14 26 30 Figure 11 Example Time Initialization File Initializing the RTC ensures that the start time and individual time stamps can be correlated to an absolute time the year month day hour minute second and fractional second An uninitialized or reset of the RTC will lead to indeterminate time stamps After unplugging the logger from the USB port the logger will load the time txt file when it is activated either by pressing the on off button or if the rebootondisconnect option is active Therefore there is a delay between when the time txt was created and when the logger actually loads the time information For most applications this simple method of initializing the clock results in sufficient accuracy 3 2 7 Memory Card The X16 4 stores data to a removable 8GB microSD flash memory card and is compatible with microSD
7. ample data in Figure 10 Table 5 Example Data Conversion Raw Data Low Gain Converted Data p Converted Data oe 69 2040 06 16 2014 09 10 12 010 0 996094 64 2059 06 16 2014 09 10 12 030 1 005371 48 l 2068 06 16 2014 09 10 12 050 1 009766 54 2050 06 16 2014 09 10 12 070 1 000977 62 2063 06 16 2014 09 10 12 090 1 007324 57 l 2075 06 16 2014 09 10 12 110 1 013184 62 l 2045 06 16 2014 09 10 12 130 0 998535 49 l 2061 06 16 2014 09 10 12 150 1 006348 30 2098 06 16 2014 09 10 12 170 1 024414 58 l 2072 06 16 2014 09 10 12 190 1 011719 66 l 2063 06 16 2014 09 10 12 210 1 007324 54 l 2057 06 16 2014 09 10 12 230 1 004395 To determine acceleration in g s divide the raw data by 2048 A g is 32 174 ft sec 2 or 9 807 m sec 2 3 2 6 Real Time Clock A real time clock RTC is integrated into the X16 4 and is used to determine time for each line of data recorded The RTC is set using a text file named time txt located in the root directory of the microSD card The system looks for the time txt file upon booting If the file exists the time stored in the file is loaded to the RTC and the time txt file is deleted The time information in the time txt file must be in the exact yyyy MM dd HH mm ss 24 hour format occur on the first line and end with a newline character Figure 11 provides an example time txt file that will initialize the RTC to
8. blink Make sure the battery is charged Check the battery disconnect jumper is set properly The logger could be operating correctly but the status indicators are turned off Check the statusindicator option in the config txt file I press the on off button the blue LED blinks once per second but the red LED does not indicate logging The deadband setting is set too high and the logger is waiting to detect an event The logger is in standby mode waiting for a start time to occur Check the config txt file for the start stop settings The blue LED blinks slowly The microSD card is not present or is corrupted Check that the card is inserted properly and the card is not corrupted I press the on off button but the logger records only for a short period of time Check that the battery is fully charged The microSD card is full and data files must be deleted The logger seems to ignore the config txt file and use default settings Check that the config txt file is properly formatted and not corrupted Each setting should occur on a separate line Some IT organizations implement an automatic encryption of all removable media devices This will encrypt the config txt file and the logger will not be able to access the file Do not allow encryption of the device June 2014 Rev New 15 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 Problem Reso
9. d space characters are ignored Lines starting with a semicolon are treated as comments and ignored by the system The system will use the default settings listed in Table 3 if the config txt file is not found Do not use the Windows Notepad editor because it does not terminate new lines properly GCDC recommends Windows Wordpad or Notepad to edit the config txt file June 2014 Rev New 5 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 Table 3 Configuration File Tags and Descriptions Valid Settings deadband An integer between Sets the deadband to a range expressed in counts 0 and 32767 A new sample is recorded if any sensor axis exceeds the previous recorded reading by the deadband value deadbandtimeout An integer between 3 Specifies the period in seconds when a sample is 0 and 65535 recorded regardless of the deadband setting This feature ensures periodic data is recorded during very long periods of inactivity dwell An integer between 1 The number of samples recorded after a deadband 0 and 65535 threshold triggered event microres Off The presence of this tag sets the device to record time stamps with 0 1ms effective precision rebootondisconnect off on disconnect The presence of this tag causes the system to start recording after disconnect from a USB port samplesperfile An integer greater 28896 The number of lines of data per data file before a than 0 new file is created samplerate 12 25
10. e A June 2014 Rev New 9 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 Example B The deadband and dwell settings configure the device to record at least 5 seconds of data when a change greater than 0 1g is detected The deadbandtimeout setting forces a sample write every hour Example X16 4 Config file set to 25Hz samplerate 25 trigger at 0 1g deadband 100 record 5 seconds of data dwell 125 force a write every hour deadbandtimeout 3600 set file length samplesperfile 30000 p LEDS on statusindicators normal Figure 8 Configuration File Example B Example C The logger must be turned on with the on off button It will enter a standby mode blue LED blinks while it waits for the start time The logger will start recording at 10 30am and turn off at 2 00pm The logger will record constantly at 400Hz and create 51 data files in the 3 5 hours The micro resolution is activated to provide the best timing precision at the 400 Hz sample rate Example X16 4 Config file set to 400Hz samplerate 400 activate precision timing microres record constantly deadband 0 deadbandtimeout 0 set file length samplesperfile 100000 set logger to turn on with clock starttime 30 10 stoptime 00 14 LEDs on statusindicators normal Figure 9 Configuration File Example C 3 2 5 Data Files The X16 4 creates a new data file when the system is boo
11. e blue LED blinks when the X16 4 is recording data in standby mode or is connected to a computer via the USB port The red LED 1 blinks when data is written or read from the microSD memory card In data logging mode the period at which the red LED1 blinks depends on the sample rate and other configuration settings The red LED3 will light when the lithtum polymer battery is charging and it will turn off when the battery is fully charged The blue LED2 and red LED1 will flicker during user initiated shutdown The statusindicators tag in the system configuration file turns off or changes the brightness of the red LED1 and blue LED2 status indicators see section 3 2 4 10 Disconnect f Top Side Figure 4 LED Indicators June 2014 Rev New 4 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 3 2 3 Battery The X16 4 is powered by a internal hardwired 500mAh lithium polymer rechargeable battery The internal battery management system recharges the battery when the X16 4 is plugged into a USB port or attached to a USB 5v power adapter The red LED3 turns on when the battery is charging and off when the battery reaches full charge The battery provides approximately 20 hours of operation sampling at 800 Hz with the deadband set to zero maximum data recording capability Reducing the sample rate does not increase the operating life significantly The battery is not used when the system is connected to a compute
12. e is limited primarily by the lithium polymer battery capabilities Table 1 Operating Conditions Parameter Value Temperature Range Operating 5 F 130 F 20 C 55 C Temperature Range Storage 5 F 80 F 20 C 25 C Relative Humidity Operating and Storage lt 90 3 2 1 Sensor The X16 4 uses the Analog Devices ADXL345 3 axis digital accelerometer sensor Table 2 lists the basic sensor and logger performance parameters but refer to Analog Devices for detailed sensor specifications The sensor output is over sampled and processed through a Finite Impulse Response FIR filter See section 3 2 5 1 for a detail description of the data format Sensor orientation is illustrated in Figure 3 Table 2 Accelerometer Sensor Characteristics Acceleration range Ll Zero g Offset Love Inter Axis Alignment Error f i ae Sensitivity Deviation Cross Axis Sensitivit The accelerometer sensor is based on microelectromechanical systems MEMS technology and is not affected by magnetic fields Glue a magnet to the bottom of the plastic enclosure to facilitate easy attachment to iron surfaces June 2014 Rev New 3 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 Figure 3 X16 4 Accelerometer Sensor Orientation 3 2 2 Indicator LEDs System status is indicated by three LEDs see Figure 4 The blue LED2 blinks once per second indicating a properly operating system Th
13. fter removing from the USB port attach the X16 4 logger to the target object The logger is small and light weight so double sided tape Velcro or a spot of cyanoacrylate glue are sufficient methods of attachment Press the button located at the rear of the enclosure to initiate data recording see Figure 2 The red LED1 will blink as the configuration file is accessed If the time txt file is present the RTC is initialized with the time written in the file The blue LED2 will begin to blink at a 1 second interval indicating the system is operating The red LED1 will blink periodically as data is written to the microSD card To stop recording press and hold the button for about 3 seconds The red LED1 and blue LED2 will blink rapidly for 2 seconds and then turn off Release the button and the X16 4 turns off Data recording is restarted by pressing the button again 66 99 The data recorded to the files must be converted to determine acceleration in g units Divide the Ax Ay Az columns by 2048 to determine g units See section 3 2 5 2 for a complete discussion of data conversion Figure 2 Starting the X16 4 June 2014 Rev New 2 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 3 2 Electrical The X16 4 is protected from general handling conditions by the plastic enclosure but is not protected from adverse environmental conditions such as rain sweat splashes and water submersion The temperature rang
14. he stoponvusb tag stops data logging operations when a 5v supply is detected on the USB connector Add the rebootondisconnect option so the logger will resume recording when removed from the 5v supply This configuration is convenient for halting data logging while charging the battery from a USB power supply Without the stoponvusb option default the device switches power from the internal battery to the USB 5v and continues to log data 3 2 4 10 statusindicators The brightness intensity of the LED status indicators is defined using the statusindicators tag and valid settings of normal high and off 3 2 4 11 Example Configuration Files Example A The following configuration records data at 100 hertz Deadband and deadbandtimeout are set to zero so the logger will record constantly at the set sample rate Each data file is 90 000 lines long which is 15 minutes of data The status indicators are set to high brightness The logger is activated with the on off button rebootondisconnect is not active Example X16 4 config file 7set sample rate available rates 12 25 50 100 200 400 800 samplerate 100 record constantly deadband 0 deadbandtimeout 0 set file size to 15 minutes of data samplesperfile 90000 set status indicator brightness statusindicators high 7 rebootOnDisconnect see X16 4 user manual for other config options Figure 7 Configuration File Exampl
15. he micro resolution option should be implemented at sample rates greater than 200 hertz to provide the best timing precision The power saving features of the X16 4 are disabled in micro resolution mode and battery life is shortened accordingly Micro resolution is best suited for applications requiring precise timing such as vibration analysis and is recommended for sample rates above 200 Hz The standard timing precision default of 1 milli second is suitable for most general applications such as monitoring human motion 3 2 4 5 rebootondisconnect The X16 4 incorporates an on off button for initiating and terminating the data recording process Data recording is automatically started upon disconnect from a computer USB port if the tag word rebootondisconnect is included in the configuration file 3 2 4 6 samplesperfile samplesperfile defines the number of data lines each file can have before a new file is created This tag controls the size of the data files into easily manageable lengths for later processing This setting is loaded as a signed 32 bit integer which can translate into very large data files The user should exercise caution before setting large files and test the end user application for data limitations 3 2 4 7 samplerate The samplerate tag defines the data rate in Hertz or samples per second Valid sample rate settings are 12 25 50 100 200 400 and 800 Hz p The X16 4 uses a digital MEMS
16. lution I plug the logger into a USB port but the PC does not indicate an external drive present The microSD card is not present in the logger or is not inserted properly Check that the card is fully inserted into the logger The microSD card is corrupted or damaged Reformat the card or replace the card The on off button could be jammed in the plastic enclosure and the logger is stuck in the off state Check that the button moves freely and clicks when pressed The USB connection could be faulty or the extender cable if present could be faulty Remove the extender cable and plug the logger into another USB port The start time in the data file header is incorrect Initialize the RTC The Z axis data is missing in the file No it s present but the column headers are shifted in your spreadsheet due to the presence of the headers tag The logger is stationary but it registers 1g This is normal and indicates Earth s gravity is fully operational and stable But the logger actually registers something other than 1g when stationary The sensor will exhibit a slight offset error Add or subtract the appropriate amount to correct the error A 3 axis tumble calibration test is the best method to determine the sensor offset error for all three axis The errors are particular to the sensor and are normally consistent throughout all data sets The logger is exhibiting inconsis
17. mation and followed by event data entries Table 4 lists the valid header tags although not all tags may occur in the header Each data line contains a time entry and the raw accelerometer sensor readings from the X Y and Z axes The time entry is seconds elapsed from the start time recorded in the header Add the elapsed time to the start time to determine the complete time record of the sample The last line of the final data file records the reason for the termination such as shutdown switched off shutdown low battery shutdown max files exceeded shutdown vbus disconnect or connected to computer The line is designated as a comment with a semicolon Table 4 Data File Header Tags E June 2014 Rev New 11 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 3 2 5 2 Data Conversion The X16 4 records the raw digital data from the accelerometer sensor This helps reduce processor load increase sample rate capability and avoid data errors due to floating point calculations The X16 4 logger over samples the sensor 4 times the selected sample rate requested in the config txt file The over sampled data is processed through a Finite Impulse Response filter 64 tap N4R4M2 The resulting 16 bit data or 65536 discreet counts covers the full range of the 16g sensor Therefore each discreet count equates to 32 65536 2048 counts g Table 5 lists the converted data using the ex
18. polymer battery charges using the USB power and provides approximately 20 hours of data recording at 800 Hz Figure 1 X16 4 June 2014 Rev New 1 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 3 1 Operating Instructions The following instructions outline the steps to begin using the X16 4 Step 1 Step 2 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7 Ensure the internal lithium polymer battery is fully charged by plugging the X16 4 into a computer USB port The red LED3 will turn off when the battery is fully charged see section 3 2 3 Plug the X16 4 into a computer and allow the computer operating system to register the device as a Mass Storage Device Configure the X16 4 by editing the appropriate tags in the config txt file using a simple text editor In Windows do not use Notepad as the editor does not terminate new lines properly GCDC recommends Windows Wordpad or Notepad to edit the config txt file Refer to section 3 2 4 for a complete list of configuration options If necessary initialize the RTC clock by creating a time txt file see section 3 2 6 Once the time txt file is saved immediately unplug the logger and press the on off button to activate The logger will load the time txt file and initialize the clock Initializing the RTC ensures the data files include the correct year month and day and that the data samples can be correlated to absolute time A
19. r USB port A 5v supply via the USB connector provides extended operation of the device independent of the internal battery Common USB power adapters or USB battery packs for consumer electronics can provide the required 5v supply The logger does not implement power saving features when connected to an external power supply so power consumption will be higher than when using the internal battery The data logger may draw up to 250mA from the USB supply to recharge the battery Plugging multiple data loggers into a USB hub can exceed the power capacity of the hub This can cause brown outs of the logger and possibly damage the microSD card The logger is always on maintaining the real time clock and will eventually discharge the battery completely after several months The battery must be charged occasionally or remove the battery disconnect jumper to completely deactivate the device for long term storage Keep in a cool 20 C 68 F dry environment to avoid damage of the battery 3 2 4 System Configuration Options The X16 4 is configured using a set of tags and settings stored in a text file named config txt which is located in the root directory of the microSD card The system reads the configuration file at boot time Table 3 lists the configuration file tags A tag is followed by an equal sign and an applicable tag setting A line finishes with a newline character Ox0A Tags are not case sensitive Tab an
20. ted or when the maximum number of data lines is reached in the previous data file A system boot condition occurs when the on off button is pressed 5v power is restored to the system via the USB connector or when the X16 4 is removed from a computer USB port with the rebootondisconnect feature enabled Data files are placed in a folder named GCDC and are named data XXX csv where XXX is a sequential number starting with 001 The system will create up to 999 files At the beginning of each file a header is written describing the system configuration and the current time when the file was created Figure 10 represents an example data file June 2014 Rev New 10 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 Title http www gcdataconcepts com X16 4 Analog Dev ADXL345 Version 736 Build date Jun 13 2014 SN CCDC10161313928 Start_time 2014 06 16 09 10 12 000 Temperature 31 25 deg C Vbat 4034 mv SampleRate 50 Hz Deadband 0 counts DeadbandTimeout 0 sec Headers time Ax Ay Az 015 22 69 2040 036 24 64 2059 056 18 48 2068 076 22 51 2050 097 24 62 2063 e117 4 57 2075 37 3 62 2045 158 15 49 2061 178 20 30 2098 1 98 24 58 2072 218 33 66 2063 e239 29 917 2057 PS CO CO BOS OOO OS Figure 10 Example Data File 3 2 5 1 Data Format Data is written to files in comma separated text format starting with the file header infor
21. tent behavior the LEDs stay on or blink slowly or the logger does not mount to a PC Remove the battery disconnect jumper see Figure 4 wait 10 seconds and then replace the jumper Disconnecting the battery resets the logger but does not affect the files on the microSD card The RTC will require initialization June 2014 Rev New 16 of 16 www gcdataconcepts com
22. une 2014 Rev New 6 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 Deadband set at 0 1g Captured Data Actual Profile Samplerate at 40 hertz 0 0 1 0 2 0 3 04 05 0 6 Figure 5 Graphical Illustration of the Deadband Feature 3 2 4 2 deadbandtimeout deadbandtimeout defines the period in seconds when a sample is recorded by the device regardless of the deadband setting This feature ensures periodic data is recorded during extended periods of inactivity A valid setting for the deadbandtimeout is an integer between 0 and 65535 3 2 4 3 dwell The dwell tag defines the number of consecutive samples recorded at the set sample rate after a deadband threshold event The deadband threshold event occurs when a sensor reading exceeds the last recorded value by the deadband setting A valid dwell setting is an integer between 0 and 65535 Deadband set at 0 4g Dwell set at 20 samples Samplerate at 40 hertz Captured Data Actual Profile 0 0 0 2 0 4 06 0 8 1 0 12 14 Figure 6 Graphical Illustration of the Dwell Feature June 2014 Rev New 7 of 16 www gcdataconcepts com USB Accelerometer Model X16 4 3 2 4 4 microres The microres option sets the device to record time stamps with 0 1ms precision In micro resolution mode the time stamps are recorded as XX YY Y YZZ where XX are seconds YYYY are 0 1 milliseconds and ZZ are spurious digits that should be ignored T
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