How Accelerometers Work in Smartphones and Where They’re Going

The modern day accelerometer can arguably be one of the great inventions of our time. That being said, many people don’t know what accelerometers are and how they work. Simply put, an accelerometer is a device that can detect axial changes in orientation. This technology is used most often in today’s smartphones to tell your screen when to rotate. But, the applications of accelerometers are more far-reaching than this.

History of Accelerometers

The micro-accelerometer that we know today is vastly different from its ancestor. The resistance-bridge-type accelerometer was developed and used as early as the 1920s. These early devices weighed about a pound and were quite large by today’s standards at roughly 3/4 inch by 2 inches by 8 inches in size. These sensors were placed in bridges and aircrafts to sense directional changes, record vibrations of turbines and even detect earthquakes.

How Accelerometers Work

Imagine a weight on a spring. If you hold the spring vertically and dangle the weight, it will stretch the spring. If you invert it, the spring compresses. If you measure how much the spring stretches in relation to where it is anchored, you can calculate the force of gravity. Using a series of these springs on different axes, you can determine which direction an object is oriented.

Now, the trick is to fit this complex mechanical device into a microchip. Essentially, engineers figured out how to use the unique chemical properties of silicone to create a seismic mass—the equivalent of the weight attached to the spring in the above example. Then, through the use of a differential capacitor, they are able to measure the distance the silicone has traveled in either direction. This makes it possible to read the orientation and velocity of the mass.

Although this sounds complex, this process has been automated through the use of tiny machines, or microengines, with gears that rotate 5,000 times a second. This makes it possible to shrink these devices down to 500 microns (1/50th of an inch) across, which is a mind-boggling feat considering the mechanical complexity.

Applications of Accelerometers

Today’s accelerometers are mainly used in smartphones. App developers, especially, have tapped into accelerometer’s functionality for gaming and fitness apps. You may have downloaded one of the many gaming apps that allow you to control or steer an object, such as a race car or a metal ball in a tilt maze, simply by tilting your phone. Some apps have even attempted to use the accelerometer as a method for scrolling, which sounds better in theory than it works in reality.

Possibly the most buzz-worthy uses are found within wellness tracking applications, which use the device’s accelerometer as a pedometer. Since most people carry their smartphones with them everywhere and health and wellness is growing in popularity, this type of technology is going to continuously be developed. For example, Apple unveiled the M8 Motion Coprocessor chip in the iPhone 6. Not only does this chip count your steps and rotate your screen, but it also can detect changes in barometric pressure (which determines your elevation) and calculate your distance traveled.

Limitations of Accelerometers

Although accelerometers work really well when worn on the wrist or when in a pocket, when it comes to other types of exercise such as pushups or weight-lifting, they’re not so good at picking up these motions. Not being able to detect different types of movements as well as the intensity of the movements has been a real sticking point for active people and athletes wanting to measure their progress and workout effectiveness.

Future of Accelerometers

The possibilities are far reaching for accelerometers. For example, there is a 9-axis motion stylus sensor that allows designers to create realistic paint spatters. Or, you might be able to control a wheelchair simply by tilting your smartphone—it has already been done by amateurs to control four-wheeled toys.

Outside of smartphone use, accelerometer technology is already being developed for use by rescue workers. One firm has even developed a chip small enough to be implanted into clothing. This technology could be used to measure electrocardiograms (ECG), breathing rate and skin temperature to help determine whether an individual is in distress or simply performing their job. For example, a sharp increase in heart-rate with an absence of movement could indicate that the worker has been incapacitated. Bottom line is that this technology could save lives in the future.