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I have had the same digital watch model for many years. Although they inevitably break again and again, I continue to buy the same model (A Casio 53W). I now have quite a collection of them sitting on a shelf for no real reason, but today when I was cleaning up I decided to take one apart.

Inside, I found that the keypad was actually quite interesting. Here's a picture.

photo

I was curious how it actually worked. I couldn't find any connectors; only multiple stacked layers of plastic with a conductive material leading from each button.

How is the signal from the button interpreted by the components inside?

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It's probably an array of buttons, but with a confusing looking layout. Where the MCU will compare which row and column is live. Here is a button array available from eBay for an Arduino.

Button Array

You can see that there isn't a pin for every button, only for every row and column.

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  • \$\begingroup\$ Ah yes, I see the little dots on the top and right of my picture. Thanks! \$\endgroup\$ Jul 24, 2015 at 12:37
  • \$\begingroup\$ Those dots look like cross layer vias. The connection to the controller is likely made with one of those rubber elastomer contracts to the row of narrow trace ends near the bottom. \$\endgroup\$ Jul 26, 2015 at 18:06

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