I'm looking to hack together a keyboard by taking an existing keyboard and connecting it to switches that I'll assemble separately.

What I want to know: What should be the electrical properties of the switches that I'll buy? I'm new to this so I'm not sure whether I need "mom off", "mom on", SPST, SPDT... Please tell me which one should be used for a keyboard.

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    \$\begingroup\$ Be sure the keyboard you intend to hack actually uses mechanical switches. Many modern low-cost keyboards use capacitive sensing instead. It's cheaper to produce and more reliable in operation. \$\endgroup\$ – Dave Tweed May 14 '13 at 14:52
  • \$\begingroup\$ @DaveTweed If that is the case, what switch could be used to replace the capacitive sensing, if any? \$\endgroup\$ – Ram Rachum May 14 '13 at 17:40
  • \$\begingroup\$ You could try putting a small capacitor (100 pF? -- may require some experimentation) in series with a SPST momentary (normally open) switch. \$\endgroup\$ – Dave Tweed May 14 '13 at 18:02

Keyboard keys conduct electricity when you press them down so you want normally open momentary press switch. To find where a button that you press is (for instance the letter "C", try to follow the lines where the switch goes and then check for electrical conductance with a multimeter (or a battery with an LED) when you press the button down. When you press it, the resistance of the leads should go from infinite ohms to close to 0 ohms.

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  • \$\begingroup\$ Thanks! What about SPST, etc? \$\endgroup\$ – Ram Rachum May 14 '13 at 17:41
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    \$\begingroup\$ I think it would be momentarily on because it is on the moment you press it and turns off when you release \$\endgroup\$ – skyler Oct 26 '13 at 22:31
  • \$\begingroup\$ Here is a typical mechanical key switch. Any momentary on switch will do, but be sure it is rated for low voltage dry contacts, has a low enough on resistance, has a contact design that minimizes bouncing, and is mechanically suited to the application. \$\endgroup\$ – RBerteig Jan 2 '15 at 21:40
  • \$\begingroup\$ Add a transistor like a MOSFET if you want to control high current applications with it \$\endgroup\$ – skyler Jan 3 '15 at 14:56

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