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ADXL362BCCZ-R2 Arkusz danych(PDF) 37 Page - Analog Devices |
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ADXL362BCCZ-R2 Arkusz danych(HTML) 37 Page - Analog Devices |
37 / 44 page Data Sheet ADXL362 Rev. B | Page 37 of 44 Example: Implementing Free Fall Detection Many digital output accelerometers include a built-in free fall detection feature. In the ADXL362, implement this function using the inactivity interrupt. When an object is in true free fall, acceleration on all axes is 0 g. Thus, free fall detection is achieved by looking for acceleration on all axes to fall below a certain threshold (close to 0 g) for a certain amount of time. The inactivity detection functionality, when used in absolute mode, does exactly this. To use inactivity to implement free fall detection, set the value in THRESH_INACT to the desired free fall threshold. Values between 300 mg and 600 mg are recommended; the register setting for these values varies based on the g range setting of the device, as follows: THRESH_INACT = Threshold Value [g] × Scale Factor [LSB per g] Set the value in TIME_INACT to implement the minimum amount of time that the acceleration on all axes must be less than the free fall threshold to generate a free fall condition. Values between 100 ms and 350 ms are recommended; the register setting for this varies based on the output data rate. TIME_INACT = Time [sec] × Data Rate [Hz] When a free fall condition is detected, the inactivity status is set to 1 and, if the function is mapped to an interrupt pin, an inactivity interrupt triggers on that pin. Startup Routine The following startup routine configures the ADXL362 for a typical free fall application. This routine assumes a ±8 g measurement range and 100 Hz output data rate. Thresholds and timing values can be modified to suit particular application needs. 1. Write 0x96 (150 codes) to Register 0x23: sets free fall threshold to 600 mg. 2. Write 0x03 to Register 0x25: sets free fall time to 30 ms. 3. Write 0x0C to Register 0x27: enables absolute inactivity detection. 4. Write 0x20 to Register 0x2A or Register 0x2B to map the inactivity interrupt to INT1 or INT2, respectively. 5. Write 0x83 to Register 0x2C: configures the accelerometer to ±8 g range, 100 Hz ODR (output data rate). 6. Write 0x02 to Register 0x2D to begin measurement. Implementation of a complete fall detection application is described in the AN-1023 Application Note, Fall Detection Application by Using 3-Axis Accelerometer ADXL345. POWER Power Supply Decoupling Figure 46 shows the recommended bypass capacitors for use with the ADXL362. ADXL362 GND INT1 INT2 CS SCLK MISO MOSI SPI INTERFACE VS VS CS VDD I/O VDD I/O CIO INTERRUPT CONTROL Figure 46. Recommended Bypass Capacitors A 0.1 µF ceramic capacitor (CS) at VS and a 0.1 µF ceramic capacitor (CIO) at VDDI/O placed as close as possible to the ADXL362. Supply pins are recommended to adequately decouple the accelerometer from noise on the power supply. It is also recommended that VS and VDD I/O be separate supplies to minimize digital clocking noise on the VS supply. If this is not possible, additional filtering of the supplies may be necessary. If additional decoupling is necessary, place a resistor or ferrite bead, no larger than 100 Ω, in series with VS. Additionally, increasing the bypass capacitance on VS to a 1 µF tantalum capacitor in parallel with a 0.1 µF ceramic capacitor may also improve noise. Ensure that the connection from the ADXL362 ground to the power supply ground has low impedance because noise transmitted through ground has an effect similar to noise transmitted through VS. Power Supply Requirements The ADXL362 is designed to operate using supply voltage rails ranging from 1.8 V to 3.3 V. The operating voltage range (VS), specified in Table 1, ranges from 1.6 V to 3.5 V to account for inaccuracies and transients of up to ±10% on the supply voltage. The ADXL362 does not require any particular startup transient characteristics, except that it must always be started up from 0 V. When the device is in operation, any time power is removed from the ADXL362, or falls below the operating voltage range, the supplies (VS, VDD I/O, and any bypass capacitors) must be discharged completely before power is reapplied. To enable supply discharge, it is recommended to power the device from a microcontroller GPIO, connect a shutdown discharge switch to the supply (Figure 47), or use a voltage regulator with a shutdown discharge feature, such as the ADP160. ADXL362 GND INT1 SHUTDOWN NOTES 1. THE ADXL362 SUPPLIES MUST BE DISCHARGED FULLY EACH TIME THE VOLTAGE ON THEM DROPS BELOW THE SPECIFIED OPERATING RANGE. A SHUTDOWN SWITCH IS ONE WAY TO DISCHARGE THE SUPPLIES. VIN R1 INT2 CS SCLK MISO MOSI SPI INTERFACE VS VS CS VDD I/O VDD I/O CIO Figure 47. Using a Switch to Discharge the ADXL362 Supplies |
Podobny numer części - ADXL362BCCZ-R2 |
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Podobny opis - ADXL362BCCZ-R2 |
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