Creative Design of Printed Circuit Boards

With this instructable, my goal is to inspire you to think creatively about the possibilities of printed circuit board designs. Although my project is still a work in progress, the focus is more on the design and thought process than the end result.

I would also like to emphasize that the techniques I used were on the "low tech" side. What I mean by that is that I designed the PCB layout without using any specialized software and utilized a single sided copper clad board which I etched myself with readily available chemicals. My design is a bit unusual and I hope it inspires you to do something a little different and encourages you to think creatively about your PCB project.

I frequently disassemble discarded electronic items that are either broken or have outlived their usefulness. I often have boxes of parts I've saved lying around in my basement. In this case, my inspiration came from a box of RGB LEDs which I had saved from flatbed scanners, many of which came from printer/scanner combo units. The idea came to me to arrange these in a radial "starburst" pattern in order to create a light display that sits on a plant shelf and faces an exterior front window. Since the LEDs are RGB, I can wire them to a microcontroller in order to create color variations and moving patterns.

At this point, it's a good idea to reflect on your project and identify the problem areas, and corresponding solutions. Ultimately, you will want an overall plan to follow for constructing your project. That's not to say that some unexpected problems might arise and may have to be solved after the fact, but it's a good idea to have addressed the so called "big rocks" that are key to making your project work. Here I describe my general thought process:

The LED "bars" harvested from the scanners, are actually "light" pipes with a small RGB LED at one end. This allows the entire bar to illuminate. The main challenge was to figure out how to attach them to a central "hub" and wire them back to the controller. Due to the geometry of the LEDs and in order for the light to face forward with respect to the hub, the pins had to be at 90 degrees from the flat surface of the hub. Therefore, I settled on a main circular PCB that serves as the hub along with eight vertical "fins" that would attach to the hub. But since the fins must both be mechanically and electrically connected to the hub, how would I accomplish that? After some thought and imagining, I settled on the following:

1. Epoxying the fins vertically to the board.
2. Creating traces that line up between the hub and the fins. Then join them at the intersection with solder "fillets". The solder fillets also have the advantage of providing additional mechanical strength to the bonding of the fins with the hub.

There will need to be 8 LEDs x 3 colors = 24 wires to the hub, plus one additional for common power (note: the LEDs are common anode). I have some four conductor wire which I will use so six cables (plus an additional wire for power) will need to be routed to the hub. I should mention that I considered placing some, if not all electronics within the hub itself, but that wasn't practical from a space standpoint given the size of the star. I also considered placing only the current limiting resistors for the LEDs in the hub, but I also decided against that since I didn't want to commit to specific values of resistors which I could easily place on an external breadboard (at least initially) for the base unit which contains the micro controller and the associated electronics. I also noticed that not all bars had exactly the same luminosity, so I think it is important keep the electronics flexible. Although the electronics will initially be on a breadboard, I may later decide to commit them to another home made custom PCB.

Another problem that needed to be solved is how to mount the star. I chose to use some old curtain rod I had saved and attach it to the hub. I will make another circular backing plate, attach it to the hub PCB using standoffs, and then attach the curtain rod to holes drilled into the backing plate.

Finally, there are the electronics. Since multiple LEDs will be lighted simultaneously, I don't want to drive them directly from the output pins. Instead, I will use an external power supply and drive the LEDs using NPN transistors. There are 8 LEDs x 3 (RGB) = 24 outputs required. Due to the number of outputs, I plan on using 74HC595 shift registers to multiplex the outputs. The Arduino library contains a function called "ShiftPWM()" which is designed to utilize shift registers and allow for each output to control the brightness of its corresponding LED via PWM (Pulse Width Modulation). Once that is working, the rest will be determined by my level of creativity in programming interesting light patterns!

Now that I have a general plan of attack, it's time to get to work and design the PCBs required for the hub and fins!

Getting Started:

Most of the time, I create single sided PCBs for my projects. You can do a lot with them. Obviously, one of the main disadvantages of single sided boards is that you don't get the flexibility of routing connections through two layers (top and bottom) and may have to design in a few places for jumper wires. For me, it hasn't really been much of a problem, perhaps because so many of my circuits are not that complex. In addition, I tend to create "modules" and try not to pack too much onto a single board.

Although I have access to automated PCB design tools, I rarely use them. I have found that I can be very productive simply using a very low tech drawing tool such as MS Paint. In fact, the boards I created for this instructable were designed using paint. Please do whatever works best for you, I'm just letting you know that there are some "low tech" approaches such as mine, that can yield impressive results. I use templates which I found here: Complex CAD Software vs Simple Paint Programs. Oftentimes, I will modify and extend these templates for my own particular needs.

My design utilized a radial trace near the periphery of the hub that serves as the power rail. This rail provides the common (+5 volts) to all 8 LEDs. Each fin connects to a single 4 pin LED (common power + R + G + B). The traces on the fins align to the common power rail along with separate traces for each RGB channel. These channels radiate longitudinally across the board and terminate on pads which will connect to the cabling that will eventually be routed through the curtain rod and back to the base electronics.

When preparing your pattern, pay special attention to which side of the board you want it to appear on. You may need to make a mirror image of your pattern depending upon which side of the board the traces are to appear. Also, any readable text must be mirrored if it is to appear correctly on the bottom side of the board. For this project, my traces appear on the top of the board and I forgot to consider that initially so my first attempt failed. Fortunately, I was able to turn "lemons into lemonade" by using that board as my hub "backing board".

Finally, I drew some mounting holes. The holes on the outer edge are for standoffs to connect the circuit board to the identically sized backing board. The central hole was used as a guide for an adjustable circle cutter which I would later use to cut out the board.

I choose to etch my own PCBs. Since the purpose of this instructable is not to detail that activity, I recommend searching the internet for appropriate tutorials. My own process consists of printing the PCB pattern to glossy magazine paper using the so called "toner transfer" method. After printing, I iron on the pattern which transfers the toner to the copper side. Although Ferric Chloride is often used as an etchant, I typically use a mixture of muriatic acid and hydrogen peroxide as these are cheap and readily available. If you decide to etch your own PCBs, please be sure to follow all safety precautions such as wearing gloves and appropriate eye and respiratory protection. The chemicals are nasty. Also, be sure to dispose of them properly. Again, there are plenty of good tutorials and videos on how to etch your own PCBs.

There are many ways to cut a PCB board, one way is to cut it by hand with a hack saw or a coping saw. In my case, I happened to have a circle cutting bit which, as you can imagine, worked well for a circular circuit board. If you go this route, you must clamp the workpiece down securely, and again, use all appropriate safety precautions (which is beyond the scope of this article). For square PCBs, I have used a scroll saw or a small band saw, but as I said before, all of this can be done with simple hand tools. Finally, the component and other mounting holes were drilled using my dremel tool with an appropriate drill bit.

Once the hub and fins were ready, I glued each fin radially using a small amount of epoxy resin glue on the edge of each fin. In order to ensure that each fin is perpendicular to the hub, I placed a small square metal bar adjacent to the fin in order to align it while the glue dried.

Finally, I soldered four solder "fillets" which electrically and mechanically bond each fin to the hub. I then used a multi-meter to verify electrical connectivity between the hub and the fins in order to assure that no adjacent traces were shorted together.

The real world is "messy". Sometimes problems creep up along the way that you hadn't anticipated. Sometimes these would have been difficult to predict beforehand, other times you may look back with a head slap and realize "I should have thought of that!".

In my case, the pins of some of the LEDs are in a bit of a zig-zag arrangement (see picture). I knew that, but didn't think that would be a problem, especially if the mounting holes I drilled were large enough. It turned out later that these would not fit flush with the PCB. There was not enough pad area to drill larger holes for them to pass through, and since I had already fabricated the board with all of the fins attached, I had to come up with a workaround. I ended up cutting some "shims" from pieces of 1/8" thick lucite and drilling 1/16" holes in them. These were sufficient to be placed over the "zig-zag" area leaving the straight part of the pins exiting on the other side. It works. You might ask "why not just straighten the pins with some needle nose pliers?". Well the wire is very rigid and this is a sensitive part which can easily detach, so I didn't think that was an effective solution. If I had to do it over again, I would simply make the pad areas on the fins larger in order to accommodate 1/16" holes. The disadvantage of doing that is that the PCB would not make a rigid connection with the pins, it would rely on the solder joint only. That may be OK, and I did have rigidity issues anyway.

Since rigidity of the light bars was another problem I had to solve it. I solved it by fabricating some metal tabs to help support the LEDS and soldering them in, along with some strategic use of superglue. I did this in a way so as to be "reversible". In other words, if I ever needed to replace an LED, it should be possible to do so without ruining anything other than the bad LED itself. It's still a bit fragile with these long light pipes emanating from the star, but it is rigid enough to remain intact with reasonable care while working on it. Eventually, it will sit undisturbed on a plant shelf, but I will need to be very careful in the mean time!

On the face of the starburst, I will be re-purposing an old hard drive platter to cover the face of the circuit board. The backing board from the failed first PCB attempt will be used as the backing board of the hub, mounted on standoffs. The curtain rod will be mounted to this backing board and to the stand which was made from an old CRT base and a larger foundational rod which came from a broken "Swiffer" vacuum. The wiring will run through the curtain rod, into the base, then out a grommet hole to the electronics. When the project is completed, I will post an update.

I hope that I've inspired you to do something creative. Don't let the fear of creating a PCB stop you. I have described how this can be done with very little investment and in a "low tech" sort of way. But most importantly, be creative and don't be afraid to try something different. I ended up creating a circular PCB with radial fins and components mounted in two dimensions, a rather unusual design. This concept could be extended to create PCBs with all sorts of geometries. I could even imagine someone making a 3D PCB in the form of a dodecahedron! So don't be afraid to go a little crazy with your designs. It's not as hard as you may think, so give it a try!

One year later, here is what the finished Starburst display looks like. I now have it sitting on a plant shelf above my front door facing outside through a big window. The controller has an infrared sensor which allows me to change from one of many programmed light sequences.