Bench Talk

I recently received a notebook as a gift at work. This notebook was cooler than most. On the outside, it had the company logo and was bound in leather (or faux leather). So far, so good.

When I opened it up, it provided a real surprise. There wasn't the traditionally regular-lined paper, nor were any clean, white blank sheets staring back at me. Rather, it was the grid graph paper featuring small squares everywhere.

Receiving this notebook made me flash back several decades ago to recording my high school physics experiments (in a similar but not as nicely bound notebook). In physics class, my classmates and I would be called upon to emulate famous past experiments. One we were asked to reproduce was the Italian polymath Galileo Galilei’s (1564–1642) inclined-plane experiment involving steep incline and shallow inclines (Figure 1). His experiment helped to displace Aristotelian conceptions of physics by demonstrating that objects experienced uniform acceleration due to the effects of earth’s gravity.

Figure 1: Illustration of Galileo's inclined-plane experiment involving steep incline and shallow incline. (Source: Mouser)

My notebook was full of measurements outlining masses (grams, g), slope angles (Θ), sin values of the slopes (sinΘ), duration times (seconds, s). Many physics experiments were done like this, including studies of the laws of motion emulating Isaac Newton (1642–1727) and demonstrating things such as F (force) = m (mass) * a (acceleration) or simply: F=ma. The net result after collecting data was usually to assemble the data from tabulations made on the left side of the page and turn them into various Cartesian coordinate graphs and functions on the right side of the open page.  

French mathematician René Descartes’ (1596–1650) coordinate system enabled points in three-dimensional space to be uniquely plotted out by a set of numerical coordinates defined by mutually orthogonal axis, called x-axis, y-axis, and z-axis. Algebra could now be easily applied to geometry.

Electronic component technology has advanced a long way in the decades since I found myself learning the basics of physics in the lab. Today, tri-axis accelerometers can easily calculate forces on all three axes simultaneously. Tri-axis accelerometers make collecting XYZ axis information easier than learning your ABCs.

One electronics manufacturer making tri-axis accelerometers easier than learning your ABCs is Kionix. Kionix, a ROHM Semiconductor Group Company, is a manufacturer of silicon (Si) Micro-electromechanical Systems (MEMS) accelerometer products (Figure 2). MEMS accelerometers are microelectromechanical systems that measure the static or dynamic force of acceleration. Kionix makes MEMS accelerometers, including a variety of tri-axis accelerometers.

Figure 2: Kionix, a ROHM Semiconductor Group Company, is a global leader in the design and fabrication of high-performance, silicon-micromachined MEMS inertial sensors. (Source: Kionix)

Kionix introduced the KX003-1077 Tri-axis Accelerometer (Figure 3). The KX003-1077 Tri-axis Accelerometer offers four extended user-configurable g-ranges (±2g, ±4g, ±8g, and ±16g) and three resolution modes (8-bit, 12-bit, and 14-bit). The accelerometer consumes <2µA at its lowest power setting and offers sampling rates from 1Hz to 1600Hz. It delivers lower noise performance, exceptional shock resiliency, stable performance over temperature, and better timing accuracy than their previous generation accelerometers.

Figure 3: The Kionix KX003-1077 Tri-axis Accelerometer with a digital I²C interface and motion detection/wake-up interrupt offers up to 14-bit resolution and user-selectable g-ranges. (Source: Mouser)

Kionix creates mechanical silicon structures, which are essentially mass-spring systems that move in the direction of the applied acceleration. The capacitance accelerometer senses changes in capacitance between microstructures located next to the device. If an accelerative force moves one of these structures, the capacitance will change, and the accelerometer will translate that capacitance to voltage for interpretation. The accelerometer further utilizes common-mode cancellation to decrease errors from process variation, temperature, and environmental stress.

A separate Application Specific Integrated Circuit (ASIC) device packaged with the sensor element handles all of the signal conditioning and digital communications for the KX003-1077 accelerometer. The complete measurement chain is composed of a low-noise capacitance to voltage amplifier, which converts the differential capacitance of the MEMS sensor into an analog voltage that is sent through an Analog-to-Digital Converter (ADC). Users can access the acceleration data through the I²C digital communications provided by the ASIC. In addition, the ASIC contains all of the logic to allow the user to choose data rates, g-ranges, filter settings, and interrupt logic.

The KX003-1077 accelerometer comes in a 2mm x 2mm x 0.9mm Land Grid Array (LGA) plastic package and operates from a 1.7V_DC–3.6V_DC supply. It uses regulators to maintain constant internal operating voltages over the range of input supply voltages. This results in stable operating characteristics over the range of input supply voltages and virtually undetectable ratiometric error.

Conclusion

The world is a place full of motion where many things are on the move. Sensing motion can be as easy as learning your ABCs. Reflect for a moment, and you'll quickly realize that tri-axis accelerometers from Kionix make it easy to sense motion and movement in XYZ as easy as ABC. Wished the classical dynamics of spinning tops I studied in physics was as straight-forward.