Kevin Cuzner's Personal Blog

The computer

In November I purchased the parts for a new computer since mine was getting very old (I got it in 2006 and even then it wasn't exactly top of the line). I put it together and it has been performing admirably for a couple months now. I was researching graphics cards and it occurred to me that I would have to move my hard drive up a slot to fit a large graphics card in my case.

After moving stuff around inside

So, I opened the case and started moving stuff around. I also decided to re-organize the cables so that they wouldn't be dangling precariously above the CPU fan by stuffing them behind the HDD cage. During that process I took some strain off the SATA cables (they are kind of stiff and I think they were putting undue stress on the sockets on the motherboard, so I moved them around so that they wouldn't be so convoluted). After finishing all this it occurred to me that my case would look sweet if I were to add some LEDs to it. I then set out to install some LEDs.

The grille and power connector

In the front of the case there is a plastic piece that covers the metal body of the case and also holds the power button, reset button, and HDD light. This case has a grille on it to allow air to pass through into the front fan (if I had one installed).

I decided that this grille could look awesome if it had some backlighting. I had considered using a lighted fan for this purpose before, but since fans are mounted on the inside of the case it would project the shadows from the internal metal structure onto the plastic grille, ruining the effect. I decided to mount some white LEDs on the inside of the plastic piece pointing towards the inside of the case so they could shine on and illuminate the part behind the grille to give a "glowing" effect. Here is what I used:

• Some spare really thick black matte cardstock my sister let me have (she is into artsy things)
• 4 White LEDs that I had lying around
• A 15Ω resistor to limit the current (4 LEDs @ 25mA each comes to 100mA at a voltage drop of 3.5V)
• A .1" header I had in a parts box
• Some wire
• Some tape

The spider wires

I started out by soldering the header to some wires to take the 5V and GND line off of the small .1" power connector in my computer. I then put the resistor on the positive rail and then split everything off into 4 wires (8 in total: 4 power, 4 ground). The result looked rather like a spider in my opinion. After that it was a relatively simple job of soldering the long lead of the LEDs to the positive rail and the other side to the negative rail. Thus, the LED assembly was completed.

Matte board and aimed LEDs

The more difficult part was attaching the matte board to the metal part of the case and then aiming the LEDs. The matte board was necessary because without it the LEDs reflected a little too well off the metal of the case and they could be clearly seen through the grille. I cut the matte board into two pieces large enough to cover the metal on either side of the grille and used tape to hold it in place. One hitch came up with the wires going to the front of the case: the hole for the wires was right beneath one of the grilles and was not easily covered by the cardstock. I ended up just basically laying the cardstock over the hole and wires and moving them around so as to not be visible through the grille. The next bit of matte board I used was to create a shroud of sorts around the HDD and power lights since the LEDs were bright enough that they shined through the bezels for those lights as well. I then spent a while aiming the lights until I was satisfied and then I put the computer back together so I could enjoy my new lights.

The Final Effect

All in all my specs are as follows:

• ASRock Z68 Pro3-M Motherboard (microATX)
• Intel Core i5-2500K Processor running at the stock frequency
• 8GB G.Skill Ripjaws DDR3 RAM
• 1TB Western Digital Green HD (using wdantiparkd to counter the head parking issues)
• Rosewill RNX-N300X Wireless b/g/n card
• Apex 500W Power Supply
• Cheap DVD burner
• Cheap Rosewill card reader
• Apex microATX case with a handle (best feature!) and some LEDs
• Ubuntu 11.10 64-bit for an OS

Since I never quite finished the story about my dot matrix clock, I see no reason why I shouldn't write a bit of a continuation of my current developments. Shortly before I left on my mission for my church in November 2009, I received my boards for the dot matrix clock and assembled them. However, I ran into a problem: The displays would turn off after the voltages on the gates of the row driving mosfets reached a certain voltage and when the voltage was at a level where it would turn on the display, it had some problems with turning on and off the LEDs. Now, after I left on my mission I would think about this once in a while and I figured out the problem: I was using N-Channel mosfets with only 5V or less of gate driving voltage so they wouldn't turn on/off all the way. I am sure there are more problems than just that, but I keep kicking myself for using N-Channel mosfets instead of using P-Channel. Had I used P-Channel, the problem would have been avoided and this whole thing would have worked great. For the moment, however, this project is on hold since I am designing and building a few things that I will need in the long term here at college since I can't lug around a power supply and an oscilloscope.

So, in summary, if I were to do a re-design I would change the following:

• The row drivers would be P-Channel mosfets. This would require using something other than a 4->16 demux for a gate driver unless I could find one with inverted outputs. Even with that I would probably put some very small gate drivers (if they exist...the size restriction might be too much) as a buffer to ensure the mosfets were turning on and off properly.
• I would factor in larger tolerances. If there was one design lesson I learned from getting these boards it is that I need to make sure that I make the holes for things a little larger. It would definitely make assembly easier.
• The PIC18F4550 would be replaced for a ATMega of some sort or maybe even a small FPGA. I was running into speed problems with the 18F4550 with getting refresh rates up (I know this is contrary to previous posts, but I was starting to have problems getting 30-60fps like I wanted...even though the image wasn't showing up anyway because of the mosfets). The 12MIPS speed was just a tad too slow and so I think if I were to use a 20MIPS ATMega it would work a lot better. Also, the tools for ATMega seem to be a little more opensourced than the ones for the PIC. I say this because avrgcc runs much better on my Linux machines than the various C compilers for the PIC series. Also, my AVR programmer (a USBASP) has very good native Linux support.

Now all that is left for me to do is to figure out how I can modify the boards I have so that I wouldn't have to drop $70 again...