Building the LEDactus Project

Overview

The project is based on a PIC18F1320 microcontroller that creates a dry climate niche dweller like a cactus known as LEDactus which can produce a pleasant display while being immobile.

Details

A significant number of LEDs are being controlled in LEDactus and since the conventional way requires one I/O line to control one LED, using the PIC18F1320 could be a problem since it only has 16 I/O lines. Fortunately, a Maxim engineer, Charlie Allen, thought of a way to control more LEDs with the same number of I/O lines. When an I/O line is configured as an output, it sources or sinks current. A third state, similar to disconnecting the I/O port from the LED, is however added since microcontroller I/O lines can be programmed to function as inputs.

Three banks of 7 LEDs are used by LEDactus and the 21 LEDs can be controlled although controlling 56 LEDs is possible when the circuit is expanded. In Charlieplexing, 240 LEDs can be controlled with 16 I/O pins. The LEDs in banks are controlled by this method wherein any LEDs in the active bank can be turned ON independently as the first bank is turned OFF.