As much as I’d like to get my mind off of the sensor I’ve used for my physical computing final, it makes sense to investigate and discuss the accelerometer. It has both allowed me to realize my idea for my final project, but has also been the bane of my existence.
I’m using the accelerometer to calculate steps on the Beatwalker. I began with a pedometer, but it was very inaccurate over a step or two (though more accurate over a longer duration). I had hoped I could calibrate the accelerometer to more accurately recognize what qualified as a ‘step’. And I was able to do so, by identifying numbers, specifically on the z-axis, that are too far away from the average z-axis numbers. The z-axis number jumps when someone’s foot hits the ground with any decent amount of force. That is the outlier I’m trying to capture.
The accelerometer dates all the way back to early 1920’s, and its development is credited to B. McCollum and O.S. Peters. It weighed about one pound, and by 1923 it found a home in dynamometers (which measure force and torque), aircraft and bridges.
To this day, highly sensitive accelerometers continue to be used in the navigation systems in aircraft and also missiles. They’re also used in a wide array of applications, including detecting vibrations on machinery, measuring depth of a CPR chest compression, and in almost all smartphones and tablets to act as step counters, but also for small tasks like determining if a photo was taken in landscape or portrait mode. Accelerometers are employed in biological sciences, transportation, and for image stabilization.
The sensor measures the acceleration or g-force of an x, y, and z-axis. If the sensor is static or not opposing the Earth’s g-force in any way, the sensor reading of each axis is 0. All implemented algorithms typically find a threshold of one or all of the axis points, and when the reading is above (or below, as a reading can be a negative), the equipment is deemed to be in another state. For example, if an accelerometer in some laptops suddenly has extreme readings past a high threshold, it’s deemed that it’s in freefall and extra measures will be put in place to try to protect the hard drive and other computer components.
Accelerometers continue to be implemented in more technology as they get smaller and more rugged, with extra benefits like wireless implementation. A more recent method of making an accelerometer is with silicon, and the whole system is reportedly smaller than they eye of a fly.
The History of the Accelerometer – http://www.sandv.com/downloads/0701walt.pdf
Evolution and Comparison of Accelerometer Technologies –
Accelerometer-Based Event Detector for Low Power Applications –