Creating an 8x8x8 3D tri-color LED cube from the ground up involves a variety of tasks, including designing the base PCB on which the cube will be mounted.
Just in case you haven't been following my earlier columns on EE Times -- augmented by videos on YouTube -- I'm in the process of building a 3D 8x8x8 RGB LED cube. My project was inspired by this article by our very own Max Maxfield.
My most recent column covered the testing of the eight 8x8 RGB LED panels. In the article before that, I introduced my requirements for the base PCB on which the cube will be mounted.
In this column, I'm going to present the construction of the base PCB in some detail. Before we commence, however, I'd like to note that there are some amazingly cool videos showing the cube in action on the last page of this article.
Brief history of my PCB experience
Before we go into detail about the base PCB, let's start with a brief history of my PCB making experience thus far. If the truth be told, it's been a very long time since I designed or made a PCB. My first board -- which I designed around 30-35 years ago -- was laid out by hand using tape and rubdown transfers. I etched the board myself in a small bowl of ferric chloride. I even managed to spill an entire bowl of ferric chloride down myself. Luckily, there was a shower close by, and I jumped in fully clothed. My clothing ended up somewhat stained, but I survived the experience with all my bodily parts intact.
My next attempt was once again laid out by hand using tape, etc. In this case, the result was photographed to produce a negative, which was handed over to someone else who made the boards for me. The boards were just bare copper with no frills, and I remember being unimpressed with the result.
Around 28-29 years ago, I landed a job as a projects manager (for about 18 months) in a circuit board manufacturing company. While I was there, I had a couple of boards made. For the life of me, I don't actually remember how I drew the circuit layout, but I'm fairly sure it wasn't computer aided. These were my first double-sided, plated through-hole boards, but without solder mask or silkscreen. As an aside, my main tasks as projects manager were to commission a multi-layer circuit board line and write most of the company's standing instructions.
Approximately 20 years ago, while working as a control and instrumentation (C&I) maintenance technician at a UK nuclear power station, I had access to a copy of the EasyPC schematic capture and PCB layout tool, with which I created a couple of board designs. For some reason, I really enjoy drawing PCBs using this type of design tool, and many an hour will pass by without my even realizing it.
I also had access to a small PCB manufacturing facility, and I used it to create my circuit boards. The design was printed out on clear film using a laser printer. The film was placed on to precoated photosensitive PC boards, exposed to UV light, etched, and tin/lead plated. The boards were double-sided, but I could not have plated through-holes, and still there was no solder mask or screen print. That was my last attempt at circuit boards... until now.
Recap of the 3D cube's base PCB requirements
What do I want my base PCB to achieve? The role of the base PCB is to provide a means for mounting the LED cube. Its top surface will be on show and must not spoil the overall aesthetics. Other than surface mount connectors and some form of fixings on the underside, no components will be directly attached to this board. Separate control boards will be created that attach to the base PCB via the surface mount connectors underneath, providing a modular system that allows for easy development in the future should there be a need to change the control circuitry.
In addition, the PCB will have a white solder mask, and the top surface will be clear of through-hole component leads and solder joints, other than the 8x8 panel anode and cathode tails passing through it. Some via holes and tracks can't be avoided, so a copper fill will be used on the top surface to help disguise the tracks. I chose a white solder mask over black or any other color because I thought it would look more attractive (and it does). In hindsight, however, flat black might have been a better choice, because it would reduce the reflections of the light from the LEDs.
The LED cube is approximately eight inches wide by eight inches deep, and its center lines will coincide with the PCB's center lines. The PCB also needs to be slightly larger than eight inches to accommodate fixing it to a wooden base, so its dimensions were set to nine inches square.
To Page 2 >