Not too long ago—say 6 months ago—I designed a motion-detecting device using, it should be no surprise, an accelerometer. At the beginning of my accelerometer search, I was looking for a device that would be easy to implement—in terms of schematic capture, layout, and ease of solderability as I would personally be placing the device, by hand, on a PCB—and easy to use, that is, acquiring its acceleration data without difficulty.
Ultimately, for a variety of reasons, I decided to use a device that had none of these qualities. However, that was before Kionix, a subsidiary of Rohm electronics, released their new KX220 series of tri-axis analog accelerometers, as surely I would have investigated this series closely.
Analog Accelerometers vs. Digital Accelerometers
True, digital sensors are all around us, and although they can offer a host of features and benefits, sometimes these add-ons are unnecessary. And, perhaps more times than not, using digital devices as opposed to analog devices, increases the complexity of both adding such components to a design and figuring out how to communicate with them. Sometimes it’s just easier to use good old-fashioned analog components, and more so, as Kionix stated in a recent press release (PDF) for their KX220 series of analog accelerometers, it doesn’t always make sense to use digital devices in industrial markets: “Unlike the consumer market, with its short upgrade cycles, it often doesn't make sense in the industrial sector to cast aside existing infrastructure and directly upgrade to digital solutions due to the significant capital already invested.” So let’s take a look these new accelerometers.
Kionix KX220 Series of Analog Accelerometers
Advertised as having dimensions of 3mm × 3mm, the Kionix KX200 accelerometers aren’t the smallest devices on the market—and, by the way, they’re not the largest either. Personally, I find 3mm × 3mm to be sort of a sweet spot for these 10-pin devices regarding soldering (rework) and the required test and validation drudgery. As a side note, the accelerometer that I ended up using for my own project, as I discussed at the beginning of this article, measured 2mm × 2mm with solder pads about the same size as a gnat's whiskers, which means it took lots of patience when hand-placing the device. The KX220 series currently includes two parts: the KX220-1071 (PDF) (full-scale output range of ±20g) and the KX220-1072 (PDF) (±40g); the image below shows their dimensions.
Figure 1. KX220-series package dimensions. Image taken from the datasheet (PDF).
Getting Schooled on Accelerometers
If you’re new to accelerometers and/or the terminology, be forewarned that the KX220 series datasheets won’t provide an adequate teaching moment for you. In my experience, most accelerometer datasheets provide accelerometer-related critical definitions and parameters, albeit brief, including Sensitivity, Zero-g Offset, Cross Axis Sensitivity, Bandwidth, and Spectral Noise. But this is not the case with KX220 series, so if you’re looking for information on such parameters, you’ll have to look elsewhere.
Although the KX220 datasheets provide documentation (via hyperlinks) for the device’s power-on procedure, it would be nice if this information were included in the datasheet itself as opposed to being an independent document…just a pet peeve of mine.
And if you’re looking for soldering tips and recommendations for these devices, you won’t find them in the datasheets or in a separate (linked) document. Rather, according to the datasheet, “Soldering recommendations are available upon request or from www.kionix.com.” This causes me to wonder why I would have to contact anyone or sift through a website to find this crucial information? It should be readily available (either part of the datasheet or via hyperlink directly from the datasheet).
However, to provide the benefit of the doubt to Kionix, perhaps the information simply isn’t available quite yet. After all, these devices were introduced less than two months ago, and, if you didn’t notice, the datasheets are indeed watermarked as being “Preliminary.” So, hopefully, the soldering recommendations will find their way to the datasheets in the next datasheet revision.
Seemingly Easy to Implement and Use
This 10-pin device—actually 8-pin since two pins are no-connects—looks super easy to implement. One bypass cap (C1) and three other optional caps (C2-C4), used for externally setting the device’s bandwidth, are all the required external components. Simply attach the three outputs to your ADC and you’re off and running. See images below.
Figure 2. KX220-series device and application schematic. Images taken from the datasheet (PDF).
Figure 3. KX220-series functional diagram. Image taken from the datasheet (PDF).
Designed for the Industrial Sector
These Kionix analog accelerometers have been designed with the industrial market in mind; ±20g and ±40g accelerations will not, hopefully, be seen by your smart phone. So don’t expect to find these high-g sensors in your fancy phones or tablets. Again from the press release (PDF), these KX220 “sensors are targeted to assist in applications ranging from vibration monitoring to shock and impact detection and measurement.” They are suitable for robotics, automation, and manufacturing applications.
Have you had a chance to use these new analog accelerometers? If so, leave a comment and tell us about your experiences.