Designing Embedded Hardware

Accelerometer

Now I’m going to take a look at an interesting sensor. Analog Devices makes some really nice accelerometers, and I’m going to show you how to interface an ADXL150 to an embedded system. You can use an accelerometer for a number of applications, not just measuring linear acceleration of vehicles. The ADXL150 is a single-axis (one-dimensional) accelerometer with a resolution of 10mg and a full-scale range of ±50g. For dual-axis (two-dimensional) sensing, choose the ADXL250.

Tip

g is the unit of acceleration. One g is approximately equal to 9.8 m/sec2 (32.2 feet/second2). As a passenger in a commercial jet aircraft, you’ll experience a force of about 2g when the aircraft turns. A fighter aircraft will experience a force of around 8g when turning sharply. Without a special suit, the jet fighter pilot would black out under a force of 8g. So, the ADXL150, with a range of ±50g, can measure a significant amount of force!

Such a fine resolution means that you can use this sensor to measure gentle vibrations and shifts. You could use it in a seismometer for geophysical applications or to measure vibrations or ground shift in mines, in tunnels, or at building sites. You could use it to monitor motion and, by placing three accelerometers orthogonally get an accurate 3-D motion recorder. The same setup could also be used as a digital carpenter’s spirit level by sensing the direction of the Earth’s gravitational field. Perhaps you might use it to monitor violent physical shock, ...