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Close Enough?

Not long ago, in our coverage of 3D vision, we discussed time-of-flight as one of the approaches to gauging distance. Even though it and the other 3D vision technologies are gunning for low-cost applications, it’s easy, at this point, to view them as exotic works in progress.

Well, time of flight is now being put to use for the most prosaic of duties: making sure your cheek doesn’t accidentally hang up on you.

Of course, our phones already have this feature via their proximity sensor, installed specifically for this purpose. It detects when the phone is near the face and shuts down the touchscreen, both saving power and rendering it immune to the random input it would otherwise get as it hit your cheek now and again.

As STMicroelectronics sees it, however, the existing way of judging proximity leaves something to be desired. Right now, it’s a simple process of sending light out and measuring how much gets reflected back, a method that can depend on a lot of factors besides proximity. How often such sensors fail isn’t clear to me, but ST has come forward with a new approach: using time of flight to measure how long it takes the light (regardless of the quantity of light) to make a round trip.

They do this by co-packaging an IR LED emitter, an “ultra-fast” light detector, and the circuitry needed to calculate the distance from the measurements. It also contains a wide-dynamic-range ambient light sensor. 

Is all of that needed just to keep your phone from getting too cheeky? Well, it’s clear that that’s simply the “marquee” function they address. On the assumption that you can do a lot more interesting stuff if you can measure with reasonable accuracy how far away something is (as opposed to a more binary near/far assessment), they’re betting that phone makers will want to include it so that both they and enterprising apps writers will come up with all kinds of interesting new things to do. It changes the class of apps it can manage from digital to analog (in the sense I defined them when discussing accelerometer applications).

Used in such other applications, they’re targeting a distance range of up to 100 mm (about 4 inches for those of us that grew up with non-metric intuitive visualization). They think it will work beyond that, but they’re not committing to that at this time.

You can find more info in their release.

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