AN022 Getting Started with the KXTE9
Contents
1. d AN 022 Kion iX i Getting Started with the KXTE9 Introduction This application note will help developers quickly implement proof of concept designs using the KXTE9 tri axis accelerometer Please refer to the KXTE9 data sheet for additional implementation guidelines While Kionix strives to ensure that our accelerometers will meet design expectations by default it is not possible to provide default settings to work in every environment Depending on the intended application it is very likely that some customization will be required in order to optimize performance We hope the information provided here will help the developer get the most out of the KXTE9 Circuit Schematic This section shows recommended wiring for the KXTE9 based on proven operation of the part Specific applications may require modifications from these recommendations Please refer to the KXTE9 Data Sheet for all pin descriptions I O Vdd SDA 1 5KO 1 5KO e 10 N IO Vdd 1 9 SCL NC 2 8 NC KXTE9 NC 3 7 INT 4 6 NC 5 0 1uF Vdd Figure 1 Application Schematic 36 Thornwood Dr Ithaca NY 14850 2015 Kionix Inc tel 607 257 1080 fax 607 257 1146 10 July 2015 www kionix com info kionix com Page 1 of 9 AN 022 Quick Start Implementation Here we present three basic ways to initialize the part These can vary based on desired operation but generally the initial operations a develop2. Tilt Position Function Position Nomenclature and Reporting Tilt Position Current Indicates the current tilt position of the device Defaults to 0x20 left Tilt Position Previous Indicates the previous tilt position of the device Defaults to 0x20 left Orientation If the part is set on its edge with the part number facing the user and the pin 1 indicator is oriented so that it is in the top left corner the part is in the Y or UP position If the user then turns the part 90 counter clockwise so that pin 1 is in the bottom left corner it will be in the X or RIGHT position Continued rotation of the part counter clockwise results in the Y or DOWN position when pin 1 is in the bottom right corner and X or LEFT when pin 1 is in the top right corner Setting the part on a flat surface with the part number and pin 1 indicator facing the sky results in the Z or FACE UP state Likewise flipping the part over to expose the physical pins to the sky would be the Z or FACE DOWN state Y X Y X Z Z 7 s Top Top l eL T G i Bottom Bottom Up Right Down Left Face up Face down UP RD DO LE FU FD State Masking Each of the 6 possible tilt position states can be masked using Control Register 2 To mask an entire axis both possible states for that axis will have to be masked Note that to mask a state the bit associated with that state needs to be set to 0 Timers and thres
3. bit 2 0x04 0 Latched mode When an interrupt is triggered it will remain active on the pin until cleared 1 Pulse mode When an interrupt is triggered it will cause a short 50us pulse on the pin and clear itself Polarity IEA bit 3 0x08 0 Active Low The interrupt pin will normally be HIGH but will transition to LOW when an interrupt is triggered 1 Active High The interrupt pin will normally be LOW but will transition to HIGH when an interrupt is triggered Enable Disable IEN bit 4 0x10 0 Disabled Interrupt conditions will not be reflected on the physical interrupt pin 1 Enabled Interrupt conditions will be reflected on the physical interrupt pin a Kionix 2015 OP 10 July 2015 Kionix Page 3 of 9 AN 022 A Few Interrupt Tips Read the Interrupt Release Register to Clear In latched mode the INT_REL register must be read in order to clear the physical interrupt pin This will also clear the Interrupt Source Registers 1 and 2 and the INT bit 0x10 in the Status Register Microcontroller GPIO Interrupt Handling GPIO configuration is based solely on the connected hardware The KXTE9 can be configured to issue interrupts depending on how the GPIO is programmed to catch them if this is not the case please contact your Kionix Sales Representative Generally when an interrupt is triggered the developer should take the following steps 1 Disable GPIO i
4. silicon chip One accelerometer can be used to enable a variety of simultaneous features including but not limited to Hard Disk Drive protection Vibration analysis Tilt screen navigation Sports modeling Theft man down accident alarm Image stability screen orientation amp scrolling Computer pointer Navigation mapping Game playing Automatic sleep mode Theory of Operation Kionix MEMS linear tri axis accelerometers function on the principle of differential capacitance Acceleration causes displacement of a silicon structure resulting in a change in capacitance A signal conditioning CMOS technology ASIC detects and transforms changes in capacitance into an analog Output voltage which is proportional to acceleration These outputs can then be sent to a micro controller for integration into various applications For product summaries specifications and schematics please refer to the Kionix MEMS accelerometer product sheets at http Awww kionix com parametric Accelerometers a Kionix 2015 ae 10 July 2015 Kionix Page 9 of 9
5. ed of a time followed by the raw count for each axis x y and z respectively Select Save or Save As from the File menu to save the file Open the saved file using Excel Calculate the average of the samples This gives the noise of the accelerometer in raw counts SensorCalc This application allows the user to test and calculate the zero g offset and sensitivity parameters of the accelerometer Once the accelerometer is properly placed relative to the Earth s gravity simple mouse clicks initiate a series of test sequences that result in the display of raw count data SensorMap This application allows the user to read and write to specific registers of the accelerometer The registers and their values are all displayed simultaneously on one color coded grid d Kionix 2015 OP 10 July 2015 Kionix Page 8 of 9 AN 022 Motion This utility allows the user to test if the accelerometer has detected motion on any of the axes The user has options to change the WUF_THRESH and WUF_TIMER register values and also mask any of the axes Rotation This utility allows the user to monitor the orientation of the accelerometer It can be used to check if the accelerometer is in the face up face down left right up or down orientations The user has options to change the TILT TIMER and TILT ANGLE register values and also mask any of the axes The Kionix Advantage Kionix technology provides for X Y and Z axis sensing on a single
6. er wants to do are read back acceleration data activate the tilt position function and activate the motion detection functions These cursory solutions are provided as a means for configuring the part to a known operational state Note that these conditions just provide a starting point and the values may vary as developers refine their application requirements Read Back Acceleration Data Write 0x98 to Control Register 1 to assert PC1 Power Control bit and set the Output Data Rate to 40Hz Register Name Value S CTRL_REG1 0x1B 0001 1011 0x98 1001 1000 Acceleration data can now be read from the XOUT YOUT and ZOUT registers Activate Tilt Position Function Write 0x04 to Tilt Timer Here we assume a 100ms timer will be sufficient this is based on an Output Data Rate of 40Hz Write 0x99 to Control Register 1 to assert PC1 and TPE Tilt Position Enable bit and set the Output Data Rate to 40Hz eie Shee Value nex Biman TILT TIMER 0x28 0010 1000 0x04 0000 0100 CTRL_REG1 0x1B 0001 1011 0x99 1001 1001 Changes to tilt position state will now be reflected in bit 4 of STATUS REG INT bit bit O of INT SRC _REG1 TPS bit TILT POS CUR and TILT POS _PRE registers and also on the physical interrupt pin Activate Motion Detection Functions Write 0x04 to WUF Wake Up Function Timer 100ms based on an Output Data Rate of 40Hz Write 0x03 to B2S Back to Sleep Timer 1200ms based on an Out
7. he interrupt is not firing at all the threshold may be set too low Note that the Back to Sleep Threshold is based on the difference between consecutive acceleration samples and can be triggered based on acceleration data from any unmasked axis Once the difference between two consecutive samples is less than B2S_ THRESH the timer starts and continues counting until it expires the part goes to sleep or a sample from the same axis that triggered the timer is more than B2S_ THRESH away from the first of the two samples that triggered the timer the part does not go to sleep and the timer is reset Try shortening the timer requirements and make sure the acceleration change on an unmasked axis is less than the threshold for the duration of the timer Remember each count in the B2S_ TIMER Register is equal to 16 cycles of the Inactive Mode ODR as dictated by OB2SA and OB2SB in Control Register 3 d Kionix 2015 ae 10 July 2015 Kionix Page 7 of 9 AN 022 Accelerometer USB Development Kit Kionix offers an Accelerometer USB Development Kit that can be used to quickly begin the development of applications and firmware that incorporate Kionix accelerometers including the KXTE9 The Development Kit provides a common interface to Kionix evaluation boards For additional information regarding the development kit please refer to the Kionix Application Firmware Development Kit users manual Here is a brief description of the applications and uti
8. holds Tilt Timer This timer establishes the number of ODR cycles that a new tilt state must be active before an interrupt is triggered and the position registers are updated Tilt Angle The tilt engine uses acceleration due to gravity to determine tilt position state As such it is unable to determine the rotational position of the part when the Z axis is in parallel with the direction of gravitational acceleration This state for the purposes of the Tilt Angle variable is referred to as zero degrees The Z axis must be a certain angle away from the direction of gravity in order for tilt changes to be registered on the X and Y axes The Tilt Angle register is used to tell the engine at what angle it needs to start looking at X and Y axis acceleration instead of Z 4 Kionix 2015 o 10 July 2015 Kionix Page 6 of 9 AN 022 Troubleshooting All Interrupt Issues Make sure the KXTE9 is configured to issue interrupt signals in the way that your GPIO is programmed to handle them An oscilloscope on the physical interrupt pin can be a valuable tool to confirm physical interrupt operation Double check the Tilt Position State Mask bits in Control Register 2 Tilt Position Function and or the axis mask bits in Interrupt Control Register 2 Back to Sleep and Wake up Functions The Tilt Timer WUF Timer and B2S Timer are based on the Output Data Rate dictated by ODRA and ODRB in Control Register 1 so make sure the correc
9. lities Supported by the development kit SensorScope This application allows the user to monitor data coming from the attached sensor This data can be saved to a file or viewed in real time With only two verification steps the application will begin immediately displaying a series of graphs representing the acceleration with respect to time SensorScope can be used to measure the noise of the accelerometer Here are the steps that need to be followed to measure noise Place the evaluation board on a flat surface in the desired orientation To change the application settings select Settings from the Edit menu Using this menu the user can change the following Sampling Rate The rate in Hz at which the software queries the accelerometer for axis data Realtime Interval The amount of data in milliseconds the software will buffer and display in real time Select the capture button The application will begin capturing data immediately Captured data is written to a file and will not be viewable until after the capture has finished The status baris used to notify the user of a capture in progress The application will continue to collect data until the user clicks the Stop button or the resulting capture file has exceeded the file size limits 1Gigabyte We recommend collecting the data for at least 120 seconds Captured data will be saved as a list of comma separated values csv Each entry in the list is compris
10. n interrupt 1 Events in the Y axis are unmasked and will generate an interrupt ZBW bit 5 0x20 0 Events in the Z axis are masked and will not generate an interrupt 1 Events in the Z axis are unmasked and will generate an interrupt Timers and thresholds WUEF Wake Up Function Timer This timer establishes the number of Active Mode ODR cycles that the acceleration on an unmasked axis must be above the WUF threshold before a wake up interrupt is triggered Each count in this register equals one cycle of the Active Mode ODR as dictated by OWUFA and OWUFB in Control Register 3 WUF Wake Up Function Threshold This threshold determines how much acceleration is required in an unmasked axis in order to trigger a wake up interrupt that causes the part to transition from inactivity to activity B2S Back to Sleep Timer This timer establishes the number of Inactive Mode ODR cycles that the change in acceleration on an unmasked axis must be below the B2S threshold before a back to sleep interrupt is triggered Each count in this register equals 16 cycles of the Inactive Mode ODR as dictated by OB2SA and OB2SB in Control Register 3 B2S Back to Sleep Threshold This threshold determines the change in acceleration required on an unmasked axis in order to trigger a back to sleep interrupt that causes the part to transition from activity to inactivity Kionix 2015 ee 10 July 2015 Kionix Page 5 of 9 AN 022
11. nterrupt 2 Clear GPIO interrupt and generate desired functionality 3 Enable GPIO interrupt These steps should be taken without calling any I C transactions if done in an interrupt context because the operating system or kernel will not allow busy waiting on an I O operation during an interrupt service routine Interrupt Polling lf physical interrupts are not used a polling mechanism can be devised which checks the INT bit in STATUS REG This mechanism should then look at INT SRC REG1 and INT SRC_REG2 to determine which engine caused the interrupt and what steps should be taken before clearing the interrupt source information by reading the INT_REL register a Kionix 2015 o 10 July 2015 Kionix Page 4 of 9 AN 022 Digital Engine Operation Motion Detection The Wake Up Function and the Back to Sleep Function operate together In later parts like the KXTF9 these are combined into one function but on the KXTE9 they must both be activated at once in order to operate properly Axis Masking It is possible to mask all wake up back to sleep events which occur on a particular axis or axes This is done with the three bits XBW YBW and ZBW in the Interrupt Control Register 2 XBW bit 7 0x80 0 Events in the X axis are masked and will not generate an interrupt 1 Events in the X axis are unmasked and will generate an interrupt YBW bit 6 0x40 0 Events in the Y axis are masked and will not generate a
12. put Data Rate of 40Hz Write Ox9E to Control Register 1 to assert PC1 Power Control bit WUFE Wake Up Function Enable bit and B2SE Back to Sleep Function Enable bit and set the Output Data Rate to 40Hz Register Name Binary WUF_TIMER 0010 1001 0000 0100 0x29 0x04 B2S TIMER Ox2A 0010 1010 0x03 0000 0011 Ox1B Ox9E CTRL_REG1 0001 1011 1001 1110 Changes to motion status will now be reflected in bit 4 of STATUS REG INT bit bits 1 and 2 of INT_SRC_REG1 WUFS and B2SS bits and INT_SRC_REG2 motion direction registers and also on the physical interrupt pin d Kionix 2015 OP 10 July 2015 Kionix Page 2 of 9 AN 022 SS Timing Requirements There are several timing requirements that developers should keep in mind when working with the KXTE9 l2C Clock The 12C Clock can be up to 400Khz Power Up to Communication After the part is powered up it takes 110ms before it is ready for C communication Enable to Valid Outputs After the part is enabled PC1 bit in Control Register 1 is asserted it takes 5ms before the acceleration outputs are valid Software Reset Power On Reset Delay After a Software or Power On Reset the part takes 100ms before it is ready for C communication Interrupt Configuration The physical interrupt has 8 possible configurations based on two states for each of the three customizable variables located in Interrupt Control Register 1 Latched Pulsed IEL
13. t cycle time is used when calculating the expected timer length Tilt Interrupt Not Working Make sure that the Tilt Position engine is enabled Try shortening the timer requirements and make sure the next state transition does not occur until after the expiration of the Tilt Timer Try increasing the Tilt Angle to ensure that the engine can see the transition between the X and Y axes and the Z axis this should not be necessary if using the default value for Tilt Angle but it s worth looking into if problems continue WUF Wake Up Function Interrupt Not Working Make sure that the WUF and B2S engines are both enabled Try altering the threshold requirements to achieve desired operation If the part is waking up too easily try increasing the threshold If the interrupt is not firing at all the threshold may be set too high Try shortening the timer requirements and make sure the acceleration on an unmasked axis is above the threshold until the expiration of the WUF Timer Make sure the Back to Sleep interrupt has been triggered before trying to activate the wake up function The part cannot wake up unless it has first entered a sleep state through the Back to Sleep function B2S Back to Sleep Interrupt Not Working Make sure that the WUF and B2S engines are both enabled Try altering the threshold requirements to achieve desired operation If the part is going back to sleep too easily try reducing the threshold If t
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