Brand recognition

In automobiles and on mobile electronic devices, buttons on the dashboard, sunroof controls, and keypads all feature recognizable sounds and feel consistent across the devices manufactured by an OEM. Not only do customers recognise the sound and the feel of a switch, and associate these features with a particular manufacturer's brand identity, but they also come to expect a particular level of quality. For example, some products that exhibit a poor actuation feel and a "metallic" click may be associated with a less insulated, lower cost device, whereas a "bass-tone" sounding device with a more cushioned feel might be perceived as a higher quality product.

For example, the effects of switch "feel" combined with reliability can be demonstrated through a gearbox application. In this instance, a two-switch system is used to control one circuit, with the second switch providing a backup function in the event of a failure in the first switch. The challenge in this design is getting the two switches to actuate simultaneously in order to feel and sound like one. By designing one sound tunable switch in conjunction with a "silent" detect switch, the user only hears and feels one of the switches, even though two are being actuated. The uniform feel and sound of this two-switch design translates into the desired reliability of the end product and reinforces the manufacturers' initial branding efforts.

Sound response

Sound response, measured in intensity and frequency, is defined by the sound emitted during the actuation of the switch, while sound emission is the combination of sound intensity and sound response. The actual tuning of switches is determined by the physics of the design and the materials used in certain sound-emitting switches. As such, switch manufacturers are studying the effects of different materials used to get the device to function as a predictable sound filter. This sound intensity is defined by the correlation between force and travel and is controlled by the attenuation of the switch. Sound intensity can be described as low (<30dBa) or high (>60dBa).

In many cases, sound-tunable switches are derived from existing switch designs. Many tactile switches feature an extended life span - up to two million cycles - thus modifying an existing switch design to include sound-tunable features enables manufacturers to confirm the reliability of the device through testing, rather than have to predict its reliability. In addition to reliability, utilising parts from an existing design greatly reduces the overall cost of the switch for both the manufacturer and the customer.

Regardless of PC board size or overall product size, all the switches on the board must sound and feel identical in order to exhibit continuity across the entire application. There are several variables that effect the creation of a homogenous sound, including the actuator material and its function as a filter. By equating sound to force and travel, it's possible to measure whether a switch is actually producing the specified sound. For example, years ago PBX phone systems featured a number of key switches that all felt differently because tactile feel was determined by the spring underneath the switch. Today, through the management of materials and the measurement of force and travel, it's possible to achieve consistent continuity of sound and feel.

Visual brand recognition

Also paramount to brand recognition is illumination. Management of the LED is critical, as the emitted colour is important to each car manufacturer to achieve a precise colour type in the interior of the vehicle, as well as the same light and colour consistently across each application. The same holds true for backlighting in mobile electronics. One option is to utilise a light pipe to backlight the dashboard, for example, which will create a cone of illumination through each button. While this produces consistent illumination, manufacturers are still faced with meeting miniaturisation and cost constraints.

Illuminated switches eliminate the need for a separate LED and light pipe on a PC board. Not only does this option save space, the LED travels with the switch actuator, ensuring even distribution of light. The compact design of these switches also saves space on the PC board, enabling product miniaturisation and greater on-board functionality.

Illuminated switches, such as the ones described above, can also be customised with latching functionality (push-push) and can be specified for switching functions such as mode select and power on/off, further meeting specific customer requirements.

Maintaining switch integrity

Along with meeting branding requirements in terms of sound, feel and visual continuity, switch manufacturers must also maintain the integrity and reliability of the switch. Achieving a specified sound response and feel without affecting the mechanical characteristics of the switch are paramount. In addition, cost is always a concern to the end-user, so manufacturers are looking to provide a technical solution that offers different sound intensity responses and superior tactile feeling for an already-developed product. This allows the switch manufacturer to avoid rebuilding a completely new product, along with the associated risks and necessary investments that such development entails. Not only is the inherent reliability of the original switch present in the new design, manufacturers are then able to offer the same version of a switch with varying sound intensity levels.

Custom designs are also being integrated into previously existing switches, such as the addition of latches for improved spring-back functionality and force, domes on the PC board, high-travel, pre-travel, pre-load and overload specifications for higher accuracy and robustness, and generally making all switch components more compact.

Continuity of sound, look and feel to enhance branding efforts are best achieved through the use of sound-tunable, LED integrated switches. Rather than inventing an entirely new design, adapting existing switch designs ensures high quality, robust devices suitable for any number of automotive and consumer applications, while still meeting challenging size and cost constraints.

C&K Components | www.c&kcomponents.com

Eric Grange is Product Manager, C&K Components

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