Minimalistic library for motion detection using low cost KXTJ3-1057, 3-axis MEMS accelerometer, low-power, ±2g/±4g/±8g/±16g full scale, high-speed I2C digital output, delivered in a 2x2x0.9mm LGA plastic package operating from a 1.71V–3.6V DC supply.
| Operating mode (HZ) | Low Power | High Resolution |
|---|---|---|
| 0.781 | 1.543 | |
| 1.563 | 1.635 | |
| 3.125 | 1.922 | |
| 6.25 | 2.488 | |
| 12.5 | 3.431 | |
| 25 | 5.784 | |
| 50 | 9.821 | |
| 100 | 18.15 | |
| 200 | 34.72 | |
| 400 | 156 | |
| 800 | 156 | |
| 1600 | 156 |
- Supports all acceleration ranges and sample rates provided by the IMU
- Supports low-power 8-bit operation
- Supports high-resolution 12-bit and 14-bit operation
- Supports latched, pulsed, and unlatched interrupt modes
- Supports both "New Data Ready" and "Motion Detection" interrupt modes
- Support for disabling individual directions in "Motion Detection" mode
- Support for disabling physical interrupt pin if strict I2C operation is desired
- Handles IMU power-on sequence and provides correct start-up delays for seamless code integration
This is the constructor. addr can be either 0x0E or 0x0F depending on ADDR pin configuration (please see Table 6 of the datasheet).
Call this with KXTJ3 myIMU(0x0E) where myIMU is whatever name you wish to use for that instance of KXTJ3.
Call this to initialize the IMU. sampleRate and accRange are required. highResMode and debugMode default to false.
Sample Rates can be found in the power consumption table above. Accelerometer ranges are 2g/4g/8g/16g.
If highResMode is false the IMU will use 8-bit low power mode. If true, it will use 12-bit high-resolution mode.
If debugMode is true then debug messages will be printed to the serial monitor for all IMU communication. By default Debug Mode uses Serial for output; this can be changed in kxtj3-1057.cpp by changing the #define KXTJ3_DEBUG Serial line.
Call this to switch the IMU to 14-bit operation mode. 14-bit operation is only available with 8g or 16g ranges.
An example sketch is provided to demonstrate the use of 14-bit mode for the 16g range.
This puts the IMU into 0.9 μA standby mode. Defaults to true. Set to false to take out of standby.
This returns a float with the g reading of the specified axis. Valid axes are X, Y, and Z.
Reads the contents of an 8-bit register at address offset into a uint8_t variable outputPointer. All register names are preceded by KXTJ3_ Please see the datasheet for the names of all available registers that can be passed to offset. The basic sketch demonstrates this function by reading the IMU's KXTJ3_WHO_AM_I register, as well as by reading acceleration data registers.
Reads the contents of two sequential 8-bit registers starting at address offset into a single int16_t variable outputPointer. Very useful for reading the raw contents of axis acceleration data registers in high-resolution mode as this will handle 2's complement correctly. Please see the datasheet for the names of all available registers that can be passed to offset. The 14-Bit Mode example sketch also demonstrates proper use of this function to read axis acceleration data.
Please note that if the IMU is in 8-bit low power mode, readRegister should be used instead to read only the high byte register for each axis, followed by casting to int8_t to get the correct signed value. This is because the lower byte register may contain junk data in 8-bit low power mode.
Writes a single 8-bit value dataToWrite to the 8-bit register specified in offset. Please see the datasheet for the names of all available registers that can be passed to offset. Also note that certain registers can only be changed if the IMU is in standby mode. As changing these special registers is handled by functions exposed by this library, we recommend using this library's functions to change configuration bytes rather than directly writing to configuration registers.
intConf(moveThreshold, moveDuration, naDuration, polarity, wuRate, latched, pulsed, motion, dataReady, intPin)
This function initializes the IMU's Interrupt Engine. An overview of the system can be found below in the Interrupt Engine section, while a more in-depth description can be found in the datasheet. Example sketches for various configurations are also provided. The parameters for this function are as follows:
moveThreshold: See Motion Threshold section below. Accepted values are-2048through2047.moveDuration: See Motion Duration section below. Accepted values are1through255.naDuration: See Non-Activity Duration section below. Accepted values are1through255.polarity: Sets whether the INT pin will be activeLOWor activeHIGH.wuRate: Sets the sample rate for the motion detection function. Valid values are the same as the IMU up to100Hz. Defaults to-1to lock sample rate to the IMU's sample rate (up to 100 Hz).latched: Set totrueto use latched interrupt mode. Defaults tofalsefor unlatched operation. See Table 15 of the datasheet for more details.pulsed: Set totrueto use pulsed interrupt mode. Defaults tofalsefor unlatched operation. See Table 15 of the datasheet for more details.motion: Set tofalseto disable the Motion Detection function. Defaults totrue.dataReady: Set totrueto enable using the interrupt engine to signal availability of new acceleration data. Defaults tofalse.intPin: Set tofalseto disable triggering the INT pin for interrupts and use only I2C. Defaults totrue.
Allows you to selectively disable individual directions from triggering the Motion Detection interrupt, or reenable all directions. This function must be called after intConf to have any effect. Valid values are XNEG, XPOS, YNEG, YPOS, ZNEG, ZPOS, and NONE. Accepts up to five comma-separated values. Including NONE at any point will enable all directions regardless of other parameters. To disable all directions, please set the motion parameter in intConf to false instead.
Returns true or false if the Motion Detection interrupt has been triggered (if enabled).
If the Motion Detection interrupt has been triggered, this will return which direction triggered the interrupt. Return values are XNEG, XPOS, YNEG, YPOS, ZNEG, ZPOS, or NONE if the interrupt has not been triggered or has been reset.
Returns true or false if the New Data Ready interrupt has been triggered (if enabled).
Resets the interrupt latch if the Interrupt Engine is in latched operation mode.
This library includes an I2C error handler on all functions except axisAccel, dataReady, motionDetected, and motionDirection. Return values of all other functions are either IMU_SUCCESS or IMU_HW_ERROR. All example sketches include the use of error handling for read/write functions.
Interrupt threshold sensitivity is compared to the top 12bits of the accelerometer 8g output value regardless of the resolution chosen. This value can be anything from -2048 to 2047.
- i.e -8g (-2048/256) to 0.0039g (1/256) to 8g (2047/256)
This is the amount of time that the change in acceleration must be above the Motion Threshold before the Motion Detection interrupt will be triggered, and is a function of Duration and Sample Rate.
Please note that in the context of Interrupt Duration, only Sample Rates up to 100 Hz are supported. If the IMU is set to a Sample Rate greater than 100 Hz and the Motion Detection Sample Rate is locked to IMU Sample Rate, Interrupt Duration will use 100 Hz for its calculation.
This value can be anything from 1 to 255
- i.e. 5 event_counts / 6.25 Hz = 0.8 seconds
This is the amount of time that the change in acceleration must be below the Motion Threshold before another Motion Detection interrupt can be triggered, and is a function of Duration and Sample Rate.
As with Interrupt Duration, please note that only Sample Rates up to 100 Hz are supported. If the IMU is set to a Sample Rate greater than 100 Hz and the Motion Detection Sample Rate is locked to IMU Sample Rate, Non-Activity Duration will use 100 Hz for its calculation.
This value can be anything from 1 to 255
- i.e. 5 event_counts / 6.25 Hz = 0.8 seconds
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