Uses and functions of keypads
– Computer keyboards have numeric keypads for efficient entry of numerical data.
– Laptop computers often have special function keys that turn part of the keyboard into a numerical keypad.
– Keypads are used for PIN entry and product selection in ATMs, vending machines, and point of sale devices.
– Projected capacitance keypads can operate through thick glass and are used in shop windows and pub jukeboxes.
– Keypads are also used in time clocks, combination locks, and digital door locks.

Key layout of keypads
– Early calculators and cash registers used parallel keys with one column for each digit.
– The modern four-row arrangement of digit keys debuted in 1911.
– There is no standard layout for arithmetic operations, decimal point, equal sign, and other mathematical functions on calculators.
– The push-button telephone keypad layout was invented by John E. Karlin at Bell Labs.
– Telephone keypads also have special buttons like * and #, and some keys may bear letters for auxiliary uses.

Origin of the order difference in keypads
– The top-to-bottom order of telephone keypads resulted from research studies conducted by Bell Labs.
– The layout was found to be more efficient than the calculator layout.
– Popular theories suggest that the unfamiliar ordering of telephone keypads accommodated the slow switches of the time.
– Another theory suggests that the layout was influenced by the use of alphabetical characters in telephone numbers.
– The position of the 1 key on rotary telephones also influenced the keypad layout.

Keypad track design
– Keypad wiring methods include separate connections, x/y multiplexing, and Charlieplexing.
– Separate connections use individual leads for each key, allowing simultaneous key presses.
– X/Y multiplexing reduces the number of leads by using a 4×4 array of input and output lines.
– Charlieplexing with tri-state multiplexing allows detection of more keys with fewer I/O lines.
– Diodes can be used to prevent key ghosting and increase the number of detectable keys.

Related concepts
– Arrow keys
– Charlieplexing
– Digital door lock
– Keyboard (computing)
– Keyboard matrix circuitSources: