RGB LED Cube

I originally intended to have my projects and tutorials be on separate tabs in this blog but it turns out that blogger does not allow that to happen so instead I will have to post them on my main page. 

This first project is a really goofy sort of artsy project I did several months back when I started to seriously get into home projects. The circuit design could not be more simple and the look itself is based on similar projects from Instructables. The schematic is below. 

Figure 1. Schematic for RGB LED Cube

I used a few 4002 diodes to represent the LEDS in the schematic, which is not really accurate because they have turn on voltages around 0.7V where as the LEDS get as high as 4V but for purposes of illustration I think they work just fine. The entire circuit runs off a 9V battery and uses 3 resistors to balance the current through the three branches. The design is horribly inefficient (around 16% by power) but there are few considerations I wanted to highlight. Also, the circuit uses an SPST switch not pictured in the schematic.

First, the resistors are carbon-film 1/8W resistors. I was able to shrink the size using 330ohm resistors 1/8W resistors to drive the LEDS at 15-17mA without overloading their tolerances. The resistors can tolerate up to 125mW of power dissipation and the most any individual branch should achieve at one time is 112mW. Granted, that is pushing the limits of the part but the small size is the design's only real redeeming feature. 

Secondly, the LEDs I used are RGB LEDs that change color automatically thanks to a tiny IC built into the component. With each new color a new turn on voltage is regulated for the LED and that made it tricky to find out the worst case power dissipation of the entire system. Normally, RGB LEDs are driven by controlling the ratio of the three colors our eyes have cones for: red, green, and blue. At the time, I thought doing a full RGB display was too ambitious for a first project so I got the LEDs that did the work for me. If you would like to get the same kind, see my bill of materials (BOM) at the end of this post.

The final product (pictured below) uses a baseball display case to hold the circuit and the accent crystals. I needed something that would scatter the light from the LEDs and some of the projects I had seen online used clear marbles so I figured it was the same basic concept. 

Figure 2. The finished RGB LED Cube

I have also added a video of the cube operating in a dark room. You can actually stare at one for these for quite a long time without getting bored. Overall, it was a quick, fun project to get started with even if the design is lacking.

 

Bill of Materials

ITEM	QTY	UNIT PRICE ($)	PRICE ($)	LOCATION
RGB LEDS	3	0.16	0.48	eBay
Baseball Display Cube	1	2.99	2.99	The Container Store
1/8 W 330 ohm resistor	3	0.027	0.081	Radio Shack
Clear Luster Accent Gems	1	1	1	Dollar Tree
SPST Heavy Duty Slide Switch	1	1.57	1.57	Radio Shack
9V battery snap connector	1	0.42	0.42	Radio Shack
1.5" Round PC Board	1	1.05	1.05	Radio Shack
TOTAL PROJECT COST			$7.59