Long Life Watch Buttons

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#1
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Does anyone have a suggestion for entering a large number of operator inputs on a watch?

I am not sure what the typical watch pushbutton lifetime is but since they are normally only used occassionally to set time, date, etc and because of their very small size I suspect that the maximum number of operations is relatively small. Maybe 10,000 operations? (just a guess on my part - the manufacturers that I have contacted do not spec this).

A small joystick similar to the one on the Butterfly (200,000 operations) might be OK and are readily available. I like the tactile feedback and it works well on a watch for my application. But packaging it into a watch case and making it waterproof (or at least moisture proof) might be challenging.

Recently saw an optical joystick on an Android (it uses firmware to monitor the movement of the fingerprint across a sensor) which would be ideal but it may not available as a stand-alone product. (Google finds all the smart phones but not the joystick.)

Maybe just beefing up the pushbutton contacts is the best way to go?

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The watch switches I have seen (very few) have been open leaf contacts. Perhaps plating them with corrosion resistant metal? Rhodium, gold, platinum? Finding some ultra small relay contacts to substitute for the original contacts might work. Almost anything electronic such as hall sensors, proximity switches, or led interrupters will probably consume more current than the watch. A moving magnet and reed switch would work but I have not seen a reed switch that would fit in a watch. (doesn't mean they don't exist though)

Are you planning on using a calculator style watch?

Rick

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I think RickB is correct, most watches that I have seen also used berilium copper leaf contacts. Not sure what the failure mechanism is though. Corrosion? Leaf exeeded yield point and doesn't return? Leaf becomes deformed? Contact points actually break due to wear? Other?

Plating sounds like a good idea and may warrant more investigation. Gold will not corrode but since it is so soft might it wear off after many uses?

No, it is not a calculator watch.

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The mode of failure in my watches is lint getting in between the button shaft and the case. It somehow works its way down to the "shoulder" where the shaft steps down to a smaller diameter. This prevents the shaft from moving in far enough to cause the switch to make contact.

The fix is to remove the shaft and then remove the lint. You need to remove a snap ring about the size of a 0603 chip resistor. Replacing the snap ring is a little more tricky. A bit of luck doesn't hurt either.

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There are watches with a touch-screen (Tissot comes to mind: tissot.ch).

Markus

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The Tissot touch screen is way out of my price range. I wince when I pay $20 at Walmart. I got one for $8 at Radio Shack 10 years ago. It worked well until I stepped on it. Plastic case, you know.

I don't know how that touch screen would work. I accidentally push a button on my watch about once a month. Fortunately it just toggles from 12 hour time to 24 hour time. Another push and I'm back to normal. With a touch screen, I can envision a real mess when the screen gets accidentally touched.

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Not sure if it's applicable here, but last night I watched the latest episode of EEVblog:

http://www.eevblog.com/2010/11/29/eevblog-130-the-ucalc-credit-card-scientific-calculator-computer/

In it, Dave shows a calculator he's designed which uses capacitive buttons. Might be a good option from a wear standpoint, though it obviously won't have any tactile feedback.

Michael