I own a classic Timex watch. It cost me less than $30, and it runs for a few years on a single, inexpensive, coin cell battery. The most difficult aspect of living with this watch is finding someone to change the battery for me when it runs down. This watch tells the time, and if I’m willing to make a fussy adjustment every other month, it will also try to tell me the date of the month using digits that are too small for me to see.
I also own a smartwatch. It costs hundreds of dollars, and I have to remember to recharge it every night or two. It also tells the time and the date (in numbers large enough for me to see). But smartwatches are doing more, with new features on the way: GPS location, wireless link to a smartphone, activity tracking, heart rate monitoring, blood pressure readings, changeable color display, altimeter, cell data access, and cellphone access. They are getting more sensors with which they can monitor more biometric measurements, and in order to manage all this data, they are doing more and more processing and analysis of the data so that they can keep the results and throw away the raw data.
And all of this takes power. The sad fact is that while sensors and processors have become smaller and less expensive, battery technology has not kept pace. The energy density has remained fairly flat while other components have improved dramatically. We may get to supercaps and other novel energy storage devices, but for now, we’re looking at a world of wearable and mobile devices that have to be recharged weekly if not daily. We can’t look to batteries to solve the problem for us.
Instead, digital electronics engineers are creating components that do a lot more with a lot less power. We have had “bi-stable” display technologies for years, which only use power when the image changes (unlike the standard LCD and OLED displays used in most wearable and mobile devices). Now we have sensors and circuits designed to use minimal power when operating, and even less when they are waiting to take action. One example is the Apollo2 processor from Ambiq Micro. The table above is from a presentation made by the company that shows how the company’s chip compares with a (much older) chip. In spite of having more onboard memory and a faster processor, the older chip consumes 29 times as much power. If those savings could be carried across an entire wearable design, a device that requires daily charging with old components might only need to be recharged once per month. The watch in the image above is the Matrix Powerwatch that uses the Ambiq Micro processor. Not only does this watch not need to be charged daily, it is able to harvest enough energy from the wearer’s body heat to power the watch indefinitely without recharging. Granted, it has a limited feature set compared to other smart watches; it tells time, tracks your activity, and can sync your data wirelessly to a smartphone app, but that’s about it. All the same, that’s a huge step forward.
As low-energy devices shrink their power consumption even further, we can expect to see even more wearable and mobile devices that will draw enough power from their environment that they will never need charging. And this will give “set it and forget it” a whole new meaning that could usher in the broader use of these devices.