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We would like to build a calculator using Arduino which uses 3 digit LCD and a keypad similar to digital phones. (# for plus , * for minus) Which components and way is good enough to not to run out of I/O ports?

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  • \$\begingroup\$ With some care, you can share either the rows or columns between the display and the keyboard. \$\endgroup\$ – Chris Stratton Feb 26 '13 at 4:59
  • \$\begingroup\$ thank you very much for all answers and comments. It is my bad to not be able to check here again. We have designed the board from scratch , using the same model atmel processor on arduino uno. \$\endgroup\$ – kayhan yüksel May 23 '14 at 13:02
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Check this arduinoo calculator kit: http://www.spikenzielabs.com/Downloadables/calc/CalcBuildInstructions.pdf Software and hardware is open source. They manages to connect 17 buttons and 6 digits LED. Wiring and sketch is very easy to understand

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Not know which arduino you use, or the total number of pins you need, the basic answer is Shift Registers or (i2c/spi) Port Expanders. More specialized versions would be 7 segment led drivers (if you are using led 7 segment displays obviously), and keypad matrix ICs. If you are using actual lcd displays, it would highly depend on the display and/or controller for the display.

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  • \$\begingroup\$ He is probably looking for shields. \$\endgroup\$ – Kortuk Feb 26 '13 at 4:20

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