LED cube problem

I woke up in the middle of the night (which usually doesn't happen) with the thought that my idea of reversing the polarity of the LED in the matrix to double the number of LED I can control wouldn't work. I drew a small version on a piece of paper, and indeed: it doesn't work. There is no combination of control signals that will allow me to turn on only one LED. It's fortunate that I discovered this now, instead of after soldering the next layer of LED. I can still control the cube with 16 lines, but I'll have to use a matrix of 8x8 divided in 4 4x4 segments rather than using two 4x4x2 segments. There will be a switching issue, but at 20 MHz this shouldn't create a big problem.

Here is the first attempt at getting the cube to work. One line of one layer only, but the rest should follow quickly: the other lines are only three wires away, and the second layer is a matter of just adding the LED. Then I will have to repeat it for the next layer.

Processor board

After I cycled against and with the wind to Radioshack (the closest, but not the cheapest supplier of PCB in my area) I was able to start soldering together the board shown. It is the typical board I make, with a 6 pin ICSP for connecting the Pickit 2, a 8-12V power supply input using a 2.1mm jack (standard) and a 20 MHz resonator (not very accurate, but accuracy seems not very important in a LED cube. The speed is useful for making special effects, which I'll probably never write). As said I'm using the 16F57, mostly because I had one around and it has two full ports (PORTB and PORTC) that can be used to control the cube. PORTB will have to share bits with the ICSP, but that shouldn't be a problem. After soldering the board I tested it, and it didn't immediately work, but that was because I didn't realise the PIC16F57 is actually not a 16-series PIC, but a base model PIC. After switching the programming software to recognize base PIC, it all worked fine. My voltage meter is running out of power, so it was giving the clearly wrong voltage of 6.3V from USB and the 7805. I'll have to buy a new battery for it.

LED part 2

I know, progress is rather slow, but here is the next part, and basically the ground floor of the LED cube. I also added the required resistors. I didn't have a PCB so I couldn't hook it up yet, but I did decide on the PICmicro to use: the rather obscure PIC16F57 which happened to be in one of the boxes that I got for winning the Microchip Innovation competition. I need to check on it, but it has 28 pins so I'm pretty sure I can use two full PORT for outputting the data, which would reduce the requirement for quick switching between patterns. I already tried lighting one of the LED, and they burn rather brightly, and are visible from the side as well. I'm still not sure if the next layer should face up as well, but it is probably best if they do.

LED part 1

The LED arrived, and they were nicer than I thought: they actually look transparent, which is much more useful for the cube idea. I started soldering them together, here are the first 8. I'll probably need to devise some plastic covering to ensure that the wires don't cross once I start bending the whole thing into a proper shape.

Places to order parts

In my previous post I referenced Futurlec as a place where you can order parts. Note that they are slow, but they are inexpensive and they have some very unique items. I really like their "LCD8X2", which is the smallest LCD display I have found so far that can still display 16 characters on two lines, and is controlled by a normal HD44780.

If I needs parts quickly, I usually go to Jameco, which is around the corner of my work place. They are more expensive, but they have very good service: you can just walk in, and walk out with your parts within 15 minutes. If you order them over the phone, they can even make them ready for pick up.

For the actual PIC microcontrollers I used to use Glitchbuster, but unfortunately they disappeared. I currently still have a large amount of them from winning the grand prize of the Microchip innovation competition but dread the moment that I would actually have to order more, as none of the websites I mentioned so far carry a good assortment. I might just order them directly of Microchip's website.

Finally, for all sorts of odds and ends, like soldering irons, solder, wirewrap wire, and various PCB, I tend to visit the local Radioshack. Do not buy parts here, as they are very expensive, and inferior in quality. Just look out for those things that will make your life better.

3D LED cube

Of course I will be continuing with the ZX-jen project, but I'm also working on a display consisting of 4x4x4 LED. I ordered 10mm big LED and will soon put them together. Using a grid with two LED (opposite polarity) per crossing you can control 72 LED with 12 lines, but I think it is wiser to control two groups of 32 LED with 8 lines each, for a total of 16 lines. This way the control of each group can be done with a single PORT, allowing all LED to change at the same time without intermediate values, which could cause the display to blink LED that should remain off. This could still happen, but is a lot less likely with the new configuration. I'll write more once the LED have come in, I used Futurlec for the order, which is notoriously slow, but has nice products for an inexpensive price.