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Sensing Without (much) Power

Sensing Without (much) Power
by Paul McLellan on 04-16-2015 at 7:00 am

 Do you have one of those step-tracker things? They seem to be one of the earliest IoT devices that are actually selling in large quantities. Smartphones are also starting to contain this sort of sensor to provide similar functionality without requiring a separate device, as are smart-watches such as the Jumpy watch for kids on the right.

Do you know what the three top things people complain about are?

  • the app is no good
  • the sensor is not accurate
  • the battery life is too short

    One of the leaders at making the guts of this sort of product is QuickLogic with their ArcticLink 3 sensor hub along with the SenseMe agorithms that take raw sensor data and turn it into step counts. It can sense taps, wrist rotation, tell the difference between walking, running, cycling and swimming. Whether the device is in your pocket or not on your person. Whether you are asleep. For all I know it can even tell what else you might be up to in bed.

    QuickLogic is not responsible for the App directly, although they do provide drivers for Android devices using their hardware. But they have a lot to do with the other two complaints.

    The current version of ArcticLink has power as low as 75uW. Since it is always on, this is important. Further, since the sensor can detect “device not on person” it can further optimize system power by, for example, turning off I2C-bus since it won’t be needed until the device is worn again. The processor inside the QuickLogic sensor hub is a microDSP-like architecture. On its own the processor is just 32uW. That is a lot lower, for comparison, than the most miserly ARM Cortex microcontrollers. In a smartphone the power consumed by the sensor hub is a small part of the overall power consumption, but in smaller devices going from 150uW to 75uW is the difference between 3 days and 7 days or even 1 month and 2 months.

    The SenseMe algorithms are more accurate than other pedometers. There are really two forms of accuracy. The first is when you are actually moving and the device is at your ear, or in your backback or strapped to your arm. How accurate is the count? The other form of accuracy is when you are not actually walking: in a car, standing still and so on. Does the device correctly notice and count zero? A lot of competing devices do badly at this and it is very noticeable since the user knows that the count should be zero. Only the most anal of users is going to count 1000 steps and see if the pedometer got the correct answer.

    Another use for the hub in a smartphone is to help with device recovery. The sensor knows that the phone has been put down and can even tell that it has been dropped. The GPS location can be sent back to enable faster recovery even if subsequently the battery runs out and the phone is not reachable. If we all start wearing smart-watches there is no reason your watch couldn’t tell you exactly where you left your phone. Insurance companies are very interested in this too, since they pay out when people lose their phones, and so they have an interest in people losing them less often.

    Quicklogic is the only solution provider with the power consumption of a custom ASIC, the flexibility of an MCU and the algorithm capabilities of a software company.

    Details on the ArcticLink 3 S2 are is here.

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