SWITCHES & RELAYS FEATURE
SWITCHING TO TOUCH CONTROL
For consistent and reliable operation,
piezo switches need to be compensated for variations in the composition of piezo materials and the effects of temperature change. They also need to be configured to suit the application: to set sensitivity, detection area and cope with different overlay stiffness, etc. This requires a dedicated interface to capture the analogue signal from the piezo disc, by applying a switching threshold that takes account of both the piezo characteristics and the system requirements, and then either communicating with a system’s host processor or providing suitable outputs for direct device control. As a founding member of the Software
Enhanced Piezo (SEP) consortium, Dutch company Aito BV pioneered the use of (SEP) touch controls by developing AitoChip, a touch controller IC that addresses these interface requirements and takes care of all the compensation and configuration issues. The company’s ATB250 AitoTouch
Controller provides a combination of input and output channels to support up to 11 piezo touch buttons, each with drivers for LED indicators to provide visual feedback, along with a single buzzer output for audible feedback. The piezo sensing parameters for each
Pauli Laitinen, Chief Technology Officer at Aito explores the advance of HMI with the latest generation of robust touch controls in favour of the more traditional mechanical switch
T
ouch control is about more than just providing an interface to a display-
oriented device such as a smartphone, tablet or computer. Certainly we have become very familiar with these applications in recent years and improvements in touch technology have ensured widespread adoption. Outside of graphical user interfaces
(GUIs) there are many other markets that can benefit from touch controls. These include consumer electronics and domestic appliances, industrial and medical equipment, automotive, and even the embryonic wearable device market. However for touch controls to provide an effective replacement for mechanical switches it is vital they are robust and reliable, and deliver a quality user experience at a competitive cost. This is where Aito’s software enhanced piezo (SEP) touch control technology succeeds in overcoming the problems of other touch technologies, which either require significant button travel or will not operate with gloved hands or through metal panel overlays. Piezoelectric material, formed into discs
or ‘pills’, generates an electrical output when subjected to the pressure applied
by a finger or stylus. These discs, which typically measure 10-20mm in diameter and just 200μm thick, are sandwiched in a simple mechanical stack (figure 1) between the panel overlay and the printed circuit board (PCB), adding no more than 0.3mm to the height of the PCB. Unlike a resistive touch switch the
movement involved is minimal, less than 1µm, avoiding need for a flexible panel overlay. The overlay can even be a seamless metal surface, something that is not possible with capacitive controls that either require separate touch plates for each sensing circuit or simply would not work if shielded by a grounded metal case. Capacitive sensing is
also problematic for users wearing gloves or where surfaces are affected by liquids or other contaminants. Seamless overlays not only make it easier to avoid moisture ingress but offer considerable creative freedom in terms of design aesthetics.
/ ELECTRONICS Figure 1:
Piezo touch panels provide robust user interfaces for home appliances and industrial controls
key can be individually configured for sensitivity, detection area and other aspects of the mechanical integration, while the LED and buzzer feedback patterns can also be customised. For easy integration into existing hardware, the device offers SPI, I2
C and DEO (Digital
Encoded Output) mode interfaces for communication with a host processor. For touch panel designs that don’t require an external host processor the ATB252 controller features a Digital Direct Output (DDO) mode that allows the device to be directly configured from an EEPROM to provide a standalone solution. It supports up to six piezo touch key inputs in combination with up to 11 LED indicators and a buzzer output. The company has also created its UX
“For consistent and reliable operation,
piezo switches need to be compensated for variations in the composition of piezo materials and the effects of temperature change....”
Design Studio development tool to help streamline the creation of “user experience” (UX) designs for physical user interfaces based on SEP touch technology. Aito’s SEP technology allows the creation of seamless touch keys on any surface, replacing traditional mechanical switches and overcoming the problems of other touch technologies.
Aito
aitochip.com Enter 208 +31 (0)75 647 5530:
info@aito-touch.com ELECTRONICS | SEPTEMBER 2014 23
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