Software-Defined Surfaces: Touch Controls Without Buttons

Nov. 9, 2021
Sentons’ ST8250 processor and gesture engine enables touch-sensitive surface operation.

What you’ll learn

  • What are software-defined surfaces (SDS)?
  • How to implement gesture control on almost any surface.

Tap and swipe have become second nature for smartphone users, but this functionality hasn’t been limited to these mobile devices. Various touch interfaces like capacitive touch are everywhere. However, they normally require specific additional wiring or other hardware that must be incorporated into the design.

Implementing it isn’t difficult for simple applications such as a button, but it can get more challenging when a surface is going to be used for gesture recognition. That’s not to say it’s impossible or impractical. Rather, the functionality and cost may become a factor in the design of an application.

Sentons has added a new technology to the mix using ultrasonic-sensing technology to support what they call software-defined surfaces (SDS). Their approach is more robust, allowing it to work in areas other implementations would not, such as outdoors where water and weather come into play.

Their SNT8250 SDSwave processor includes a gesture engine designed for use with wearable applications like watches, glasses, earbuds, and fitness trackers. It can handle conventional gestures, such as swiping on areas like the legs/arms of eyeglasses (see video).

Sentons’ software-defined surfaces (SDS) allow developers to put touch controls on almost any surface from earbuds to the edge of smartphones.

The ultra-low-power chip consumes 20 µW in standby mode and 80 µW in operating mode. The gesture functionality works in the presence of water and the technology operates on almost any surface including metal. Most capacitive-touch systems don’t work with metal. The system also can be used with small displays where other touch systems may be difficult to implement. On top of that, it handles curved surfaces without any special configuration requirements. The sensor can be used with haptic feedback systems to provide a better user experience.

Sentons employs a a technique that’s similar to ultrasonic range sensing with an emitter and receiver, but the implementation is quite different because it utilizes surface waves and sensing. Piezoelectric transducers are attached to the interior of the touch surface. The transducers transmit as well as sense the ultrasonic waves that travel through substrate. Any touch on the surface, such as a finger, will affect the waveform being received. The trick is that the hardware and firmware must figure out the location and the pressure involved so it can be provided to the host.

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