Analog Angle Article

Dry switching is driving me crazy!

In the bad old days of electronics, before microamps defined our world, the front-panel switches (aka contact closures) that users pushed had to handle tens and more of milliamps. Even if they did not directly control a load, but only signaled the system or drove an intermediate relay or function, these so-called dry switches still had to have real metallic contacts, and were also somewhat self-cleaning due to a “wiping” action between contacts.

Those days are gone. In today's processor-controlled world, especially one where power consumption is critical, the front-panel switches are often a plastic-rubber composition with some conductivity added in via embedded metallic particles. It's cheap, small, thin, and suitable for multibutton, complex, compact form factors. As they say in those press releases, it's “ideal.”

Oh yes, there's one more thing: it's not too reliable, either. In the past few months I have had several home devices fail or go intermittent, including two remote controls and a cordless phone. Fortunately, I was able to open the cases and find the problem in each case: there was gunk in the switch area, a combination of skin oil, ambient dirt, and what I believe was the debris of the deterioration of the switches themselves, probably accelerated by the skin oil. I cleaned it all carefully with contact cleaner and a lint-free cloth (conveniently picked up at a trade show), and all units were working, at least for now.

There are alternatives to these low-end contact closure switches for such dry-switching applications, such as capacitance sensing and electric field sensing, or better-quality resistive-style switches. Unfortunately, they are generally too costly or the contact area needed is too large for micro-sized handheld devices with many buttons, such as the basic TV remote control, so they can't always be used. You can never be too small, thin, or cheap!

What does this poor reliability say about us and our products? We design and assemble these marvels, yet their reliability is greatly diminished by the poor quality of the switches. It's as if we assume that the user will only have the product a year or two, and then it's a toss-out, as a sort of acceptance of planned obsolescence.

I don't like this at all. Every time we design and manufacture products that self-destruct after a few years of modest use, we say that engineers can't do a good job. The public doesn't know or care that the fault is that a low-end component with inherently limited life that we used, nor should they be expected to know this.

While many users don't care since they do intend to replace the unit anyway, a reasonable percentage of the users do care. Even for those that who had planned on replacing their present unit (the euphemism is “upgrade”), that still leaves a bad image of us in their minds. And we wonder why people don't think much of engineers any more?

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