When functioning as an LED display or mechanical keypad, the use of reversed pairs of LEDs or standard diodes at the intersections doubles the 8 input matrix size from 28 to 56.
The diagram shows that eight inputs creates 16 intersections when used in an x/y array, but 28 intersections when used in a Charlieplexed array. to drive an array of LEDs.Ĭharlieplexing can be used in displays and resistive or projected capacitance keypads and touchscreens, using a simple array (shown).
A Charlieplexed digital clock which controls 90 LEDs with 10 pins of a PIC16C54 microcontroller.Ĭharlieplexing (also known as tristate multiplexing, reduced pin-count LED multiplexing, complementary LED drive and crossplexing) is a technique for driving a multiplexed display, keypad or touchscreen, in which relatively few I/O pins on a microcontroller are used e.g.
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