[Mike Bortfeldt]

The answer to your questions are in the data sheet on the web page that Don pointed you to. The typical supply voltage to this part is 3V however it can be operated at any voltage from 2.4 to 5.25 volts. At a 3 volt supply, the sensitivity is around 174 mv/g, however when the supply is bumped up to 5 volts, the sensitivity increases to 290 mv/g as indicated in the IFI document. Manufacturing variances cause each part to be slightly different from each other. However, the specifications indicate that at a 3 volt supply, the center (0 g) value will be between 1.2 volts and 1.8 volts - basically +- 20% of the center voltage. Assuming this holds true at a 5 volt supply, the 0 g value would be between 2.0 volts and 3.0 volts which gives you quite a big potential range for analog values for 0g. Typically, the parts will be very near 2.5 volts, but the specifications indicate that it is possible for them to vary significantly, but will never be outside the specified maximum and minimum values. Also the specification indicates that there could be up to a +-15% variation in sensitivity from part to part. So one part may be as low as 247 mv/g to as high as 333 mv/g. A perfect part would give you 3080 mv or an analog value of 631, but all parts are not perfect. Thus the suggestion by Don to calibrate the accelerometer by using gravity.

Mike