Capture motions with Kionix’ Tri-Axis Accelerometers and a TI’s MSP430F149. App note here (PDF)
Kionix linear 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. The output voltage is sent to the MSP430F149 ADC for conversion to a digital signal. This signal can then be sent to a serial port, an IR chip, a flash NAND for storage, a USB port, through SPI or I2C to another processor, etc.