Soldering the LEDs

This was actually a very tedious process, though I did get really good at soldering. I started off by bending all of the LEDs in the correct direction positive to negative and negative to positive.

I bought 4 1/16 inch blue strips of heat shrink, and 3 1/8 inch clear heat shrink to cover the resistors. I ended up having an entire strip of blue heat shrink left, and about half of my clear heat shrink. I measured and cut as many pieces of heat shrink as I needed for every LED.

After I cut the heat shrink, I put it on the LEDs. A few times I forgot to and had to un-solder everything, that sucked.

Then I put on the heat sinks, which was sometimes hard, because I still needed enough room to solder.

I simply melted some solder on the tip of the soldering gun and applied it to the wires. You have to make sure that you get the wires hot enough so that you don't have a cold solder.

Second I soldered the resistor.

I usually had to cut some of the LED wire off so that the resistor would fit between the two. I would use this spare wire to solder between 2 of the LEDs when they didn't reach each other.

I shrank all of the heat shrink with the tip of the soldering gun, plus, it looked cooler that way.

The final product looked something like this except with every single LED soldered.

Every single time I finished a set of 3, I tested it with a multimeter to see if the components still worked. When I was finished with every single rail, I soldered a wire along the positive sides, and a wire along the negative sides. I then tested that with a multimeter.

Through my regular camera, the final result looked something like this.

Through the IR camera, the results looked like this.

I am extremely pleased with the results I got. I wouldn't do anything different if I were to do it again. I might add more LEDs, but hey, I can still do that if things don't work out.

Works Sited:

Hewes, John. "Soldering Guide." Welcome to the Electronics Club. Web. 21 June 2010 <http://www.kpsec.freeuk.com/solder.htm>.

Resistor Specifications

Using Ohm's law, which states that voltage = current/resistance, and using Kirchoff's voltage law, which states that the sum of all the voltages in a loop must equal zero, I was able to find the desired resistance I wanted.

I wanted to use the computers power supply 5 volt output to power all the LEDs, so....

5V - IR(Ohm's law) - 3(1.6V) = 0 (1.6V is the primary operating range of the LEDs)

+----|>|----|>|----|>|---/\/\/----+

So the resistance of the resistor must equal 2.2 ohms. Thus, I searched digikey.com for some 2.2 ohm resistors. Since each resistor dissipates about 22 mW, a 1/4W resistor should do the trick. I ended up getting the OD22GJE-ND resistors.

Click here for the resistor specs.

Testing

This is probably a post I should have made a long time ago. Before everything I do, I test it. Through past experiences, I've realized that this is very important to do. You don't want to build something that takes you a few hours, then figure out that it doesn't work. I haven't taken many pictures of my testing, because, well, I'm not usually sure if I'ts going to work!

These are the LEDs that I used in my LED rails.

I also tested the IR rails, and if they would fit the plexi glass properly. I tested drilling the rails. I tested to see if the FTIR effect would work, and I tested the compliant surface. So, I've tested nearly everything so far.

I also designed a CAD model in Blender for my table, a basic guideline of what I needed to do. This showed me how much wood I needed and it what size.

To download this Blender file in .blend format, click here.

Making The Silicone-Vellum Sheet

I posted the video about how to apply the silicone to the vellum. I did a test sheet first to make sure I knew what I was doing. I also tested it out on my 1" by 1" piece of acrylic, It worked great! So I set up in a place where there would be enough air, so that I wouldn't be breathing xylol the entire time, my garage. I was going to set it up on a table, but the table I had wasn't big enough. So, I found the most level place on the floor in my garage and set up some newspaper there. The xylol is poisonous and will eat away at plastic, so you cannot use a plastic container when mixing. I bought a metal container from Home Depot.

I then poured a 1 to 1 ratio of xylol an silicone into the metal container

It's important to mix slowly so that you don't get any bubbles in the mixture. Bubbles are bad because they will stay there for an extremely long time. It took me quite a long time to stir until all of the chunks were out of the mixture. About 30 minutes of slow stirring.

You will know when you're done stirring because there will be no chunks, it will look like 1 solid mixture, and it will run off the end of whatever you're stirring with very smoothly.

It's important to pour all over your vellum sheet, not like I did. It took me about an hour to spread it all around evenly and make it look good. The sheet will become see-through, but thats okay, it's not going to stick to the newspaper.

Try to buy the finest sponge roller you can find, this will create the best texture.

I then decided to set up a light, so I could see how even the silicone was being spread.

When I was finished, I tipped the table over and set up a clean bed sheet, that I vacuumed, over the vellum. When it was dry, it stuck a little bit to the newspaper, but it didn't really matter.

My sheet was perfect, but I had a little bit of the silicone mixture that I had to throw away. :(

Building The IR Rails

To hold the IR LED's in place I need to build rails. I bought all four of the 'L' shaped aluminium rails at Home Depot for about $15. These rails will hold the IR LEDs right against the acrylic plexi glass and shine the IR into them.

I started off by measuring and cutting the rails into three foot lengths.

When cutting, I recommend you but a block of wood behind the saw to guide it. I cut every single piece at a three foot length, and I intend to angle the edges to fit together on the glass. After I finished cutting the rails, I measured every 2 inches, after the first inch, and placed a black dot with sharpie. When I finished there were a total of 18 black dots on the aluminum. After the dots were placed, I went through each rail and put a hole where the dots were using a drill press. I used a 3/8 inch drill bit, the size of the LED.

The drill left the holes a bit rough, so I smoothed them out using a filer.

The holes were a tiny bit small for the LEDs so using the drill bit, I carved them out just a little bit. When I was sure the led was going to fit tightly, I started to put them in with white silicone caulk. I used white because I accidentally bought that instead of clear, for the vellum. I applied a little bit of caulk to the LED and put it in the hole. I made sure all of the LEDs were facing the same direction, the long wire on top.

This was my finished product for every single rail:

In the future, if I could find the right size, I would use 'H' shaped rails. Those rails would hold onto the glass better. I would also be sure to use clear silicone caulk, so none gets on the tip of the LED and block light. I washed all of the LEDs after the caulk had dried.

LED specifications

I wanted LEDs that had about an 880nm wavelength so it could be picked up by any standard webcam. I also wanted the LEDs to have the smallest viewing angle possible. Though, I wanted them to be cheap as well. I ended up getting the QED223-ND LEDs from digikey.com.

You can find these LEDs here: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=qed223-ND&x=0&y=0

These LEDs were 5mm big, they had a viewing angle of 40 degrees, and they had a wavelength of exactly 880nm. The peak current is 1.5 volts, and they draw 100mA! Here are some performance curves for the LED:

Polishing the acrylic.

For best results, the edges of the acrylic need to be as clear and as smooth as possible so they will let in the maximum amount of IR light. When you buy acrylic, it comes very rough because of how they cut it in the shop. So I decided to, first, sand it with 220 grit then 400 grit sand paper.

Before the process even started the edges of the plexi glass looked something like this:

After using an electric sander with the 220 grit sand paper, the plexi glass looked something like this:

Unfortunately, with my camera, its hard to tell whats smoother than that from here on out. When sanding I had to be very careful to keep the sander level with the side of the glass. Also, I had to be careful to not stay in one spot for too long sanding, or else the glass wouldn't be level all the way across.

I went over each side with the 220 grit about 10 - 15 times each, and changed the sand paper every 2 sides. When I went to the 400 grit wet, I went over each side about the same amount, but every 2 times I stopped to get the sand paper wet again, and the glass wet again.

After each sanding session I wiped the glass down with a wet cloth to get any excess dust off. When I was done with both 220 and 400 grit sanding, on all sides, I wanted to buff out anything else that was left. To do this I found a buffer laying around my house and some polish.

I globbed on the 'scratch out' onto the glass, smeared it around, then let it dry. After about 5 minutes of drying, I buffed it all out, then wiped it down with the wet cloth.

Well, I got it extremely shiny! It should work great for the LED's.