Keyboard Matrix Interface

  
Keyboards can be slotted into two categories, at least as far as the manner that the switches are connected is co
Keyboard Matrix Interface - schematic

ncerned: those with a common connection and those with the switches arranged in a matrix. The matrix type has the important advantage that the number of connections is an absolute minimum. Such an arrangement is ideal for ICs; many of these are designed for use with a matrix keyboard. However, many keyboards are available in job lots, for instance, that apart from a common connection also have a connector for each key. Such keyboards can be connected to ICs that require a matrix type with the aid of a number of electronic switches. The principle is straightforward: each key of the keyboard controls an electronic switch that is included in a matrix. As an example, the diagram shows a hexadecimal keyboard that is arranged in a 4- -4 matrix. Each of the electronic switches is held in the open position by a pull-down resistor. The current drawn by the circuit is very small and is determined mainly by the value of the pull-down resistors and the number of keys being pressed. The CMOS switches draw virtually no current.




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