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4x4 Keypad

In microcontroller systems, devices requiring multiple keys—such as electronic locks or telephone keypads—often use a matrix keypad, especially when 12 to 16 keys are needed.

A matrix keypad, also known as a row-column keypad, is designed with four I/O lines serving as rows and another four as columns. Each intersection of a row and a column corresponds to a key, resulting in a total of 4×4 keys. This structure efficiently optimizes the use of I/O ports in a microcontroller system.

The keypad’s contacts are typically accessible via a header, which can connect to a ribbon cable or be directly inserted into a printed circuit board. In some keypads, each button connects to an individual contact in the header, while all buttons share a common ground connection.

img_keypad

More often, the buttons are matrix encoded, meaning that each of them bridges a unique pair of conductors in a matrix. This configuration is suitable for polling by a microcontroller, which can be programmed to send an output pulse to each of the four horizontal wires in turn. During each pulse, it checks the remaining four vertical wires in sequence, to determine which one, if any, is carrying a signal. Pullup or pulldown resistors should be added to the input wires to prevent the inputs of the microcontroller from behaving unpredictably when no signal is present.

Example