How the cube is made:
The dimensions of the cube will be 8 led by 8 led, by 8 led, for a total of 512 leds. The whole structure will be based on a wood board.
The concept of persistence of vision:
In this project we will exploit the persistence of vision. This phenomenon is a feature of the human eye and is responsible for the illusion that a movie is not composed by individual still images. All the animations are based on this biological dis-functioning of the human eye. If we can switch on and off the leds in a sufficiently quick time, (a few milliseconds) they will appear as if they were simultaneously on.
We use the persistence of vision because simultaneously switching all the cube leds on would require a very high electric current (in ampere). Actually, if we consider that the high brightness leds of this project require about 20 mA, we can calculate that 512 leds would require 10.24 A. This high current is hard to manage. So, what we do? We switch on a cube layer at each time! In this way the current consumption will never exceed 1.28 A (20 mA x 64 leds), which is easily supplied by a good voltage transformer. Let us suppose that we want to make the cube appear as completely switched on. To achieve that we simply have to switch on the different layers one by one at high speed. To a human eye the cube will appear as completely lighted.
How to control each led:
In order to independently control each led, we divide the cube into horizontal layers and vertical columns.
All the leds of a horizontal layer will have the cathodic contact (-) in common.
All the leds of a vertical column will have the anodic contact (+) in common.
Overall, it will be necessary to control 8 cathodic contacts to select the layers and 64 anodic contacts to select the columns. The combination layers by column will select and switch a single led.
The 8-bit shift registers:
The shift registers are composed by 1-bit memory cells connected one each other. At each clock impulse, they allow the bit flowing from a cell to the next-one. The registers used in this project are SIPO (serial input-parallel output) type. The data are charged one by one through the input bits and the output bits are simultaneously collected from the 8 outlets.
Power supply':
To power the cube and the control circuit it is necessary a power supplier with the following specifications:
- voltage: 5 volts (stabilized)
- current: 2 ampere (4 is better)
Needed tools:
- Soldering iron
- Soldering tin alloy
- Hot glue gun
- Jigsaw
Needed materials:
- 512 leds of your favourite colour
- 1 40 pin flat cable (to connect the IDE hard disk to the pc)
- 1 34 pin flat cable (to connect floppy disk to the PC)
- 1 prototype board
- 1 plywood board 20x20 cm, 8 mm thick
- Electric wire suitable for soldering (thin, flexible, and resistant)
Building:
Draw a 7x7 square grid (2.5 cm side) on the the plywood board. At the crossings of the grid lines drill 64 holes with a mesh diameter as the led size, generally 5 mm. This board will be the basis on which all the leds will be soldered. By this solid grid the leds will be evenly spaced and perfectly aligned. As explained in the intro, the cathodic contacts of each layer will be joint together. Insert the 64 leds in the board holes and bend the cathodic (-) terminal to obtain an interconnected grid.
SEE IMG. 02.1 AND 02.2
Let go out the board holes only one led terminal. It will control the layer.
Attention! Each time you finish soldering a layer, test each single led. It is convenient to discover early if a led is burned out or not well soldered.
SEE IMG. 03.1 AND 03.2 AND 03.3
Make 8 identical grids, paying attention that the led terminals going out of the board have a different orientation for each layer.
