Product How-To: The mechanics of capacitive touch sensor interfaces

Steve Barry

March 1, 2011

Steve Barry

Challenge #4: The need to differentiate

Consumer electronics is one of the quickest moving industries. Therefore competition is increasing every month, so there is a continued need to find a way to stand-out from your competitor.

To do something different to set yourself apart. Implementing capacitive sensing is a great way to do this, specifically in the following ways:

Sleek design: No one likes the clunky appearance of buttons on their devices. Think of an oven, a TV, or STB. Now imagine those same devices with completely flat surfaces, where you don’t even see the buttons until you want to see them, just smooth, reflective glass or black surface.

Then when you want to adjust the temperature of the stove, turn up the volume of the TV, or pause the show you are watching the buttons ‘magically’ appear.

This is possible through a capacitive proximity sensor and capacitive button, slider, or wheel implementations. This is not just an interface differentiator, but a complete product differentiator!

Multi-functional sensors: With mechanical solutions it is a very binary result. The button is either pressed or not.

But what if you could get one type of functionality out of a button when you have your finger on it, but not pressing it and another when you actually push it down.

Through an implementation utilizing both mechanical and capacitive buttons this enables 1-button to essentially become 2 in the same board space.

Customized feeling: What if I what to give the user a different feedback depending on the button, slider, or wheel they touch? With the first button there is no feedback required, with the second a 1-second soft response, the third a medium 5-second response, and last a strong 15- response.

With a mechanical dome switch this isn’t possible to provide varied response depending on which button is pressed. With an MCU driving both capacitive touch technology and an actuator, a large variety of haptic effects are available and can be set-up to provide a completely different feedback from button to button.

Power savings: With the coming of the “Green Movement” everyone is attempting to reduce power consumption, increase battery life by making electronics work more effi- ciently, yet without sacrificing their functionality.

Take a wireless mouse for example, when you aren’t using it you want it to save power by being in a sleep or hibernate mode, yet when you go to use it you don’t want to have to shake it and wait for it to wake-up.

This is a great example of where capacitive proximity sensing can be a game changer. As my hand approaches this sleeping mouse that has a capacitive proximity sensor in it, the mouse senses the hand and wakes it up from its sleep mode so that by the time my hand actually reaches the mouse it is ready to move with my every motion.

This addition of the capacitive proximity sensor therefore saves power, and improves the previous functionality of the standard design.

Mechanical interface weaknesses

As previously referenced, mechanical solutions have their weaknesses. By definition a mechanical solution will have moving parts and air-gaps so wear and tear is inevitable.

RIM’s most common failure in their BlackBerry phones was the trackball. Kids spill juice boxes and trail mix on the center console in the car making it so the window button no longer works.

The outdoor garage opener button rusts out because of being rained on. All of these problems are preventable by using capacitive solutions where there is no movement, no air-gap, and are water resistant.

With all of these new solutions available reduce the risk of converting from the ancient mechanical solution to the more modern capacitive solution, with all these cool new differentiators, what more does a designer want to make the change?

Atmel is asking this same question as they have available microcontrollers to drive this touch technology. It also has proximity sensing capable of greater than 6”, greater than 100- haptic effects in library formats to choose from, and easy to design with software in Atmel’s QTouch Studio (Figure 1 below).

 

Figure 1: Atmel QTouch Design Studio 4.3 allows designers to implement touch buttons, sliders, and wheels in a wide variety of applications.