Most modern smartphones can sense whether their users are holding them in the portrait or in the landscape position, accordingly adjusting the displayed image. Additionally, while playing games such as Temple Run, the smartphone can respond to tilting by changing certain functions in the game. The smartphone accomplishes this motion sensing as it has an accelerometer IC working inside it.
Apart from smartphones, several other applications make use of accelerometers. For instance, car alarms can be programmed to alert their drivers as soon as they cross a certain speed threshold. Hill Start Aid (HSA) systems depend on accelerometers to alert drivers when their vehicles start climbing a defined slope. Accelerometers tell weighing machines whether a vehicle is properly positioned before starting to take readings. Black boxes or data recorders in airplanes, trains, and other vehicles stop recording when an accelerometer decides there has been a violent incident.
Analog Devices makes ADXL313, one of such versatile digital accelerometers. The device has very high resolution of 13 bits on each of its three axes, and is capable of measuring up to ±4 g, where 1 g is the normal level of acceleration due to gravity at sea level. ASXL313 offers a 16-bit data output in a two’s complement format. The user can access this digital output through either an I2C serial interface, or a 3- or 4-wire serial port interface (SPI).
Being very small, only 5x5x1.45 mm, ADXL313 comes in a lead-free, RoHS compliant, LFCSP package and is qualified for automotive applications with a wide operating temperature range of -40°C to +105°C. The device is capable of surviving shocks up to 10,000 g. ADXL313 can work with a wide supply range of 2.0 to 3.6 V, consuming ultra-low levels of power. At a supply voltage of 3.3 V, the ADXL313 consumes only 30 µA in measurement mode, and only 0.1 µA in its standby mode.
While its embedded FIFO technology minimizes processor load for the host, ADXL313 offers an exemplary noise performance of typically 150 µg/√Hz for its X- and Y-axes, and typically 250 µg/√Hz for its Z-axis. While its user-selectable resolution is limited to a 10-bit resolution for any g value on the low side, its sensitivity is a minimum of 1024 LSB/g for any g range. On the upper side, its resolution scales from 10-bits at ±0.5 g to 13-bits at ±4 g. ADXL313 features a built-in motion detection function for monitoring activity/inactivity.
The ADXL313 3-axis digital accelerometer offers its user several flexible interrupt modes, which the user can map to two interrupt pins. Along with the built-in sensing function, the device can sense the presence or absence of motion, and detect whether the acceleration on any axis is exceeding the user-set level. The user can map these functions on two interrupt output pins, which can alert the controlling micro-controller accordingly.
ADXL313 has an integrated 32-level FIFO register to store data. This minimizes host processor intervention leading to a huge reduction is system power consumption. This low power mode enables intelligent motion-based power management and empowers the device with threshold sensing and active measurements while dissipating extremely low levels of power.
