Introduction: Z80 CPU Thumbdrive

I have broken the thumb drive case on several of my USB drives. Once again I broke one of the cases but I needed the drive urgently the following day. I really was in fear of static electricity killing it before I replaced it. My original thought was to wrap it with medical or duct tape. That thought led me to think about salvaging it. I gave some thought to brushing epoxy on it before wrapping in medical tape but that would look really tacky.

I finally decided to make a see-through epoxy case. I started to make a clay mold for the epoxy and was looking for a square edged tool about the right size for clean edges. I had a bag of 20 year old CPU and memory chips laying on the shelf above my work space and noticed the larger Z80 CPU chip was about the right size.

I started pressing it against the clay edges and all of a sudden I had a moment of eureka! It occurred to me that this old chip would look fantastic as the case! I thought for a while about the different chips I had on hand. I considered putting a CPU on one side and a 2708 glass UV erasable memory chip on the opposite side. That would have worked but it would have taken more time and fuss than I wanted to invest. I decided for the best of both worlds. I would have the CPU on one side and clear epoxy protection on the opposite side.

Go grab some old chips and dig that broken USB drive out of drawer - lets get started!

Step 1: Make the Mold

1) 15 or 30min epoxy
2) Exacto style razor knife
3) Modeling clay
4) Clay forming tools
5) Hot water and soft brush
6) Flat work surface

Take some children's modelling clay and press the naked USB into the clay to form an outline. Then press a larger outline with an appropriate tool. (I used a pencil eraser and refrigerator magnet for much of the pressing). The indentation should be about 1/8-3/16 inch deeper and wider on all sides than the actual USB device. For the half round key chain tab I used a small felt tip marker cap.

When the mold looks good, press the Z80 chip into the bottom half way up the shell. Do what is necessary for the USB to be level when laid on top. It may be necessary to place a piece of clay or other object as a standoff for the USB board to be level.

Wrap a little clay around the USB plug so that it will seal good when it is laid into the mold.

Step 2: Pour the Epoxy

Pour epoxy into the mold about 3/4 the way to the top. Lay the USB board in and add a layer of clay around the mold edge so that when more epoxy is poured the USB board will be immersed at least 1/16-1/8 inch. The joint/edge of the layers do not need to be perfectly lined up. Later the mold line will be trimmed. Now pour epoxy until the board is completely covered.

[ It is possible to make a deep seamless mold. However, my experience has been that attempting to press the clay for a deep one piece mold creates problems with distortion and the USB board is harder to position level. ]

Let the epoxy dry for 1-2hrs. The clay needs to be removed when the epoxy has the consistency of very tough hard rubber. You will need to work aggressively, you don't have much time before it completely hardens.

Remove as much clay as possible by scrapping and cutting. When there are small spots left take the device and spray it with water as hot as you can get from your faucet and still able to hold on. The hot water helps melt the clay. A lite scrubbing with a vegetable brush may help too.

Step 3: Finish the Triming

Be careful! The epoxy is still soft and can be be scratched or damaged.

Now with a razor knife (Exacto or similar) quickly but safely trim and scrap the mold edges to final shape. I like a little roundness to the corners. As you work, you will notice that the epoxy continues to harden and you will only have about 30min before it becomes quite difficult to trim.

That is about all there is to it. I suggest you wait several hours (even a day) before attempting to drill a key chain hole. I guarantee this USB drive will break the computer before the case is damaged. 

Step 4: Be Creative

An advantage to making your own USB cover is that the end result is so unique that it should serve as a deterrent for it walking away. A possible alternative would be to write your name on the PC board before pouring the Epoxy.

There are many creative options, how about a dime or picture on the PC board? Folks used to make toilet seats in a similar way and embed barb wire, sticker bushes, thorns, tacks, nails, etc. This type of thinking can be extended to this project too.

If you come up with something interesting, why don't you share it with the rest of us :)  

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