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Basic Electronics » USing Calculator as Keypad

January 16, 2011
by dgikuljot
dgikuljot's Avatar

Hey guys, I have taken many of the cheap basic function calcualtors. I was wondering, is it possible to use the calcualtors keypad as a keypad to enter numbers into the mcu. If we were to intercept the data going to the small lcd of a calcualtor, could we somehow have the mcu read that. It would be a great way to have keypad intputs to mcu for possibly a security system. Thanks

January 16, 2011
by Hexorg
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well most calculators have some really small, basic mcu's in them, so yea, you should be able to easily :)

January 17, 2011
by hevans
(NerdKits Staff)

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Hi dgikuljot,

Trying to high-jack the signals from a keypad could be an interesting project, but you can also just purchase a 12 button key pad and just interface with that. Interfacing with a keypad like that will be very similar to interfacing with just single push buttons like the one we include with our kit.


January 18, 2011
by bretm
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Note that that one is a "one common terminal" keypad which means one pin for each key, 12 pins total if you want to use all 12 keys. To reduce the pin count you'd need additional external components.

Another common type is "matrix encoded" like this one which uses one pin for each row and one for each column, or 7 pins total for all 12 keys.

January 18, 2011
by dgikuljot
dgikuljot's Avatar

Hey guys, Thanks for all the replys. Im not really planning on buying a keypad, i just though it would be interesting to link a 99 cent calcualtor to the avr 168. i was just wondering if anyones ever done that before. if not how could i read the data with the mcu. Thanks Kuljot

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