Fig 1. This mechanical switch provides an excellent tactile feel, and offers high-reliability and longevity for typically analog audio/video applications.
Fig 2. For digital applications, A/V engineers are increasingly using encoders like this dual-concentric version. The requirements of analog applications of excellent tactile feedback, rugged design, and long life remain critical for high-end equipment.
It’s been said that once audio goes digital, the need for high quality switches would basically disappear. The reasoning is that the audio path does not directly travel through the switches anymore on the digital version, so manufacturers could specify a lesser grade of component than necessary for analog audio. But several well known and highly respected manufacturers of audio, and video, products continue to demand customizable, high quality encoders and switches for their digital products. Particularly where there are special dimensions or other modifications, they have a challenging time finding digital switches/encoders that meet their specifications.
Design Criteria
In the audio/video (A/V) market, switches and encoders are often used for interface controls for different types of high-end audio gear. Therefore, a great “click feel” is as important as reliable electrical functioning. A switch should give tactile feedback when switching channels, without feeling mushy. The switches should also exhibit “low play” (side-to-side wobble), and low “black-lash” (wobble within each resting position).
Most high-end equipment manufactures insist that the feel of the switch must imply a certain level of quality, otherwise the customer believes the manufacturer is trying to save money by specifying a lesser quality control. Further, since the panel controls are the interface point (the window into the mindset of the manufacturer), it is even more imperative that the switch convey the quality that they want their brand to represent, particularly for their top-of-the-line gear. Figure 1 shows a mechanical switch that has been typically used in analog A/V applications.
Of course the issue of electrical reliability is still the primary consideration, but the feel is of equal importance. And let’s not forget ruggedness. It is quite common that accidents can happen to equipment whether the piece is in the home or out on the road. Many an expensive stereo cabinet has been pulled down on its face by playful kids or pets. Axial and lateral impact resistance is still an important consideration for these manufacturers.
For years, engineers have required mechanical, incremental single, and dual-concentric encoders for the audio market as gear has increasingly moved to digital applications. It is also clear that high ruggedization and great tactile feel are also increasingly important to design engineers. Plus, the encoder must be easily modified to meet customer’s requirements, even in small quantities. This brought on several design challenges. How could all of these requirements be met, and could they be done in both single rotary encoder and dual-concentric versions for digital applications?
Solutions
To meet the needs of audio engineers and other users, we need to design switches/encoders that are available with or without buttons, with the shaft mounted or delivered separately, and in single or dual-concentric versions. The dual concentric encoder offers the functionality of two encoders in one package, thereby saving panel space. Figure 2 shows an example of a dual concentric encoder with these features.
To add more advanced ruggedization to the encoder, using a nickel-silver or equivalent body and not plastic is advisable with brass shafts or stainless steel shafts. Note that the shaft can be modified to fit a manufacturer’s existing knob design so the proprietary look is not affected. While many of the low-end encoders for audio offer a rotational life of 35K to 50K cycles, i.e., wear is noticeable often before switch failure, this is not acceptable for many high-end applications. When using design techniques that minimize internal friction and wear and employing high-quality components, high-end switches can perform up to one-million cycles while maintaining the same feel throughout the life of the encoder. Using only gold contacts also ensures electrical continuity and performance over time.
A precision indexing design and high quality components will also create proper tactile feel. The superior life and consistent feel is evident with an indexing design that minimizes wear on the encoder’s internal mechanism components. Essentially, the user, without having to look at the unit, should be able to turn the switch knobs and count the number of positions the dial actuates by feel. This is also common in high-end mixing boards and even applies to other equipment, particularly in medical devices.
In the end, switches can be customized even in low volumes to meet specific requirements of various a/v equipment manufacturers. With differing requirements and specifications, vendors should be able to realize a custom encoder with the feel, reliability, and long-life requirements that their customers would expect when purchasing this level of high-tier equipment.