It’s no surprise that some of the biggest problems in the design of systems that involve sensors are at the interfaces. While invaluable for the decoupling of parts and their role in allowing for reuse across different implementations, the numerous challenges associated with sensor interfaces are enough to make anyone’s head explode.
In fact, in a recent survey by FierceElectronics on designing with sensors, more than one third of the respondents reported that their biggest challenge is integrating sensors into a design (see below). Dealing with interfaces even beat out the number two challenge—meeting budget constraints—another well-known and major source of engineering woe.
Several engineers had plenty to say about the pain inflicted by dealing with sensors interfaces in their design work.
“It’s a problem area because the interfaces break down into one of three, typically: I2C, SPI or serial,” says Mike Anderson, Lead Systems Architect, Huntington Ingalls Industries, Technical Solutions Division. “Serial is always a problem because there are so many variants. Voltage mismatches (5V vs. 3.3V requiring level shifters, etc.) and how many pins are needed is always a challenge. For I2C, you've got 100KHz and 400Khz versions, and often there will be conflicting addresses on the bus that need to be dealt with, requiring the engineer to actually read the data sheets.”
He went on to note that while SPI is much faster than I2C, it has limits in the number of devices on the bus.
None of these problems are particularly difficult by themselves, of course. But the fact that so many sensors have multiple interface options forces the engineer to choose and then commit to a bill of materials—and that’s where the work can pile up.
Matt Liberty, President of JetPerch LLC and a DSP, FPGA and embedded software consultant agrees, pointing out that while interfaces are valuable tools, each interface requires additional work to design and test.
“A vendor usually provides the interface implementation with only an application note or small amount of demonstration code that uses the interface. Sensor hardware interfaces are not standardized and vary across vendors and even parts, which mostly prevents reuse,” he notes.
“Each product using a sensor then has to fully implement the interface, which requires the engineer to read and interpret the documentation. With even simple accelerometers having over 50 registers, incorporating a new sensor takes time, is highly subject to human error, and is often a frustrating experience.”
Frustrating indeed, so what’s an engineer to do? More standards--and adherence to them--would help. And Liberty says that formalized interface specifications, along the lines of ARM's CMSIS SVD, and better example code would go a long way towards making sensor interfaces less painful.
For more information and insights on coping with sensor interfaces, several sessions at this year’s Sensor Expo & Conference, June 22-24, 2020 in San Jose, CA, specifically address the topic:
For more information on the conference program and all sessions, visit the Sensors Expo & Conference website.
As a FierceElectronics reader, you are eligible to use the following promotion code to receive $100 off a conference pass or for free entry to the Expo Hall: FE100
Note that Super Early Bird Rates for the Sensors Expo & Conference are in effect until February 14, 2020. Passes are limited—so act fast! Register here.