Touchless Sliders, Microcontrollers With Human Interface

in Hand

Imagine being able to control electronics products at home and in the office, not with a direct touch but with the sweep of your hand. Advanced touchless human interface technology is now within the realm of practical implementation, even for products as commonplace as the alarm clock beside your bed. We all have experienced the frustration of locating the snooze and silence buttons on an incessantly beeping alarm clock at 6:00 a.m. What if you could extend your sleep just a bit longer by simply waving your hand or tapping a virtual button to shut off the alarm without fumbling to find the clock in the dark?

Touchless Slider
The simple wave of a hand or tap of a virtual button is an intriguing product innovation not only for alarm clocks but also for an array of consumer and industrial applications, from cell phones and other hand-held devices to large appliances to factory control panels. One way to achieve this is a touchless slider, and the concept can be adapted to a great number of products that we encounter every day. The touchless slider solution comprises two or more infrared LEDs, an infrared detector and a low-power 8-bit microcontroller (MCU) based on the 8051 core.

Two infrared LEDs are independ-ently pulsed, and an infrared sensor detects the reflected infrared light. A comparison of the strengths of the two reflections indicates the relative location of the object along the single axis.

An infrared slider is quite similar to mechanical and capacitive sliders. Chances are, you have seen sound stage panels with innumerable rows of mechanical sliders. Capacitive sliders are implemented with a smooth surface and no moving parts. All three are capable of detecting movement and a set-location in a single axis and each provides intuitive control.
The infrared slider offers additional advantages:
The function is invisible and aesthetically pleasing.
The axis of measurement can extend beyond the ends of the physical elements of the slider.
The z-axis can be included in the function.
The implementation is easy to clean and leaves behind no finger oils.

Alarm Clock Example
While the touchless slider function can be added to virtually any product with a human interface, all of these advantages can be adopted by our alarm clock example. An 8051 MCU independently controls the infrared LEDs such that only one LED is enabled at any one time. The MCU responds to the output of the sensor, calculates the position of the hand and (optionally) displays the relative position of the hand with the visible blue LEDs at the top of the clock. The visible feedback might be useful for adjusting the time or as a volume control.

Sensing Gestures
In our familiar alarm clock example, a variety of gestures can be sensed with ease. A left/right motion may be interpreted as a volume control, or possibly a snooze trigger. When an object passes from left to right over the infrared LED axis, the MCU is able to synchronize the infrared LED pulses with the output of the infrared detector.

As the hand moves from left to right, the reflectivity of the red curve rises to a peak, followed slowly by the blue curve as the hand approaches the maximum reflectivity of the right-most Ir LED. The midpoint of the virtual slider is indicated where the two curves cross-over. If the hand passes in the opposite direction, the blue curve would rise before the red.
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Silicon Labs - Optical Sensor IC and 8051 Microcontroller

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Touchless Sliders, Microcontrollers With Human Interface

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This article was published on 2010/11/11