Publication date: 26 February 2008
Switches are seemingly simple components, yet they have a dual role. Not only must they perform mechanically and electrically, they must also convey feedback to the user that the operation has been accomplished. Switches are now incorporating tactile, audible and increasingly visual indication - all in a tiny package. What’s more, as an interface component, this feedback must remain consistent over the lifetime of the device – or risk giving a poor impression of the overall end equipment quality.
We all use probably hundreds of electronic switches every day. The keys on a keyboard, a mobile phone, home audio, iPod, car dash board – the list of applications goes on and on. We use switches so often that they seem simple, mundane components, yet it is the very fact that they are the main interface with a human operator that makes them more complicated.
Size is perhaps the most obvious. Either the size of your mobile phone or PDA will shrink, or it will stay the same but have increased functionality. Either way there will be less space for the components. The same is true in almost every application. With electromechanical components this can be tricky, because there is a physical current that needs to be carried, which requires certain dimensions. However, tremendous strides have been made. Only a few years ago, tactile switches were considered tiny if they measured 12mm x12mm. Now C&K’s latest devices measure just 2.6mmx3mm. In fact, KMT series are claimed to be industry’s smallest and lowest profile top actuated tactile switches with an integrated actuator (push plate). With extended application lifetime of 150,000 operations, gold and silver plating options and superior tactile feel, these switches have a profile of 0.65mm (0.45mm body height with 0.20mm actuator and 0.13mm travel). Devices have been designed into hearing aids and headsets.
Slide switches, too are now even smaller. For example, C&K’s single pole JSM series feature actuators that are just 2.5mm high actuators, making them very easy to operate. Available in single, double or triple throw styles, these 0.3A at 4VDC devices come in surface mount format and are available in tape and reel packaging.
Reliability is an absolute requirement, not only for mission-critical applications such as medical, aerospace and defence, but also because switch performance contributes so much to how a product is perceived. C&K has worldwide manufacturing facilities, but the company’s high volume manufacturing location is in Dole, France, close to an area famed for its expertise in precision engineering due to the watch industry. Currently, quality levels are being measured in single figure parts per million failure rates: in the next five years the company confidently predicts that low parts per billion failure rates will be common. Reliability has become a strategic issue for most consumers of electronic components. Recent product improvements made by C&K have seen the company’s KSR family of miniature 6x3.8x1.75mm tactile switches for the automotive and consumer electronics sectors benefit from an increase in an operational life of up to 200,000 cycles. Even more impressive, the company’s KSC industrial tactile switch series, which are only slightly larger at 6.2x6.2x2.5mm, are now rated to perform up to 1,000,000 cycles, the equivalent of 274 operations every day for ten years.
Because of the human aspect of switch operation, feedback mechanisms are becoming more and more important. It is not merely enough for a switch to work, we must know it has worked, and manufacturers are now incorporating tactile, audible and increasingly visual indication into their products.
Consistency of feedback is crucial in building customer confidence in the final equipment, which helps to improve the brand image of the OEM. As an example, certain car manufacturers require that the switches on their dashboards all sound the same. Yet one manufacturer favours a higher pitch while another prefers a lower tone. Tactile feel is another case in point. Higher quality tactile switches will usually feature a metal dome insert which requires the same amount of pressure to activate every time, and will always snap back into the same position, providing consistent feedback.
Illuminated indication of switch operation is also increasingly popular, and miniature versions are now available. As an example, C&K’s ELUM range of right-angle LED illuminated pushbutton switches are just 6mm in height. ELUM switches eliminate the need for a separate LED and light pipe on a circuit board, and are the only pushbuttons to have been designed such that the LED travels with the actuator, ensuring an even distribution of light. To increase the usefulness of these devices, ELUM pushbuttons are now available with custom-designed snap-on caps, enabling designers to incorporate standard icons – such as the standard universal power symbol or an individual design, such as a company logo or graphic.
C&K Components is the new name for the former switching components businesses of ITT. C&K was an established name in switches until its acquisition by ITT a few years ago. C&K is now a business division of CoActive Technologies, a technology company within USA private equity company Littlejohn & Co. The new C&K combines the history and experience of three of the industry’s leading suppliers; C&K Components of Newton MA, USA, the Rudolf Schadow Company of Berlin, Germany, and the Jeanrenaud switch company of Dole, France. Because of this experience, C&K Components is able to deliver custom-engineered solutions in virtually any application.
As an example of this capability, one of C&K’s major telecommunications customers had a requirement for a PCB-mount, subminiature snap switch that would fit into a very small which could be actuated in any direction. Engineers at the company proposed using the company’s ZM switch with a custom design lever. A snap-over hold-down mechanism is employed to allow lock out detection
The lever actuator lever design finally chosen resembles an upside down teaspoon. Not only does this shape enable actuation from any angle, it also increases the life of the switch as it spreads the load more uniformly across the contact than a flat blade. C&K’s design engineering capabilities enabled the company to model the modified switch in the customer’s finished product application. More, the one piece blade design of the resulting ZMA type has enabled C&K to reduce the cost of the device significantly. Applications include PCI storage devices, computer peripherals, test and measurement equipment, remote controls, automotive and medical equipment.
Switches are like every other aspect of good design: get the choice right and you’ll help guarantee functionality and enhance the quality and brand – get it wrong, and it may come back to haunt you!
