Electronics 101

After getting an inquiry about making 100 MintyBoosts (which eventually did not pan out), I started doing research this past weekend to see if I could actually do it. Because the guy wanted an older version that you can’t buy printed circuit boards (PCB’s) for anymore, the big challenge would be getting those made. All of the other parts (resistors, capacitors, inductor, microchips, etc.) seemed to be available. I knew that Ladyada, the inventor of the MintyBoost, had a lot of files available for download and didn’t seem to mind sharing her design. And given her incredibly detailed instructions on how she developed the project and how someone could make it, I figured I would just have to follow the instructions.

Turns out it wasn’t quite that simple. On her downloads page she had the current design and a couple of the earlier ones available, but not the v1.2 that I wanted. But even so, the designs are in an electronic format made for the CAD software (Eagle), but not made for production. For that I would need Gerber files.

I found a page at Hackaday that talked about how to convert files in Eagle into Gerber files for a PCB fabricator. That was pretty useful and looked like I could do it. So I downloaded Eagle’s software and tried it out.

One thing Ladyada did to get a better deal on circuit boards was she combined two boards onto one. One side of the board has rounded edges, so she put the flat sides back to back and got oval boards. Then she cut them in half for two boards with rounded edges once she received them. But her Eagle file only had one board in it. I spent a while trying to figure out how to make a copy of that board before I finally realized that the free version of Eagle does not let you do this.

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Trailing Stop

I’m not all that sophisticated an investor and mostly I am in mutual funds for the long-term. But I do buy stocks and have been kind of successful selling stocks when I get to a 20% gain and buying more share if they fall 20%. To do this I use a lot of limit orders. If I buy a stock at $100/share, I can put in a sell order that day for $120/share and a buy order for $80/share. If the price falls 20% I automatically buy more. If it goes up, I automatically sell. I like this because it keeps me from getting greedy and I don’t have to watch the market all day (or at all).

I bought some Goldman Sachs like this and when it went down 20%, I bought more, which I then sold when it went back up. Goldman has been on a yo-yo, so I’ve been able to buy and sell three times for a 20% profit each time. But I didn’t reach a 20% gain on the original shares until recently. My intention was to hold on to GS because I felt like its long-term outlook was very good and it could make a lot more than 20%. Still, it could also zoom right back down. Today it was up quite a bit and I’m into the 30% gain range. I didn’t want to sell if it would go up some more, but I don’t think I want to allow it to get below my 20% gain mark either.

So for the first time I am using a “trailing stop”. This sets a sell price a certain amount below the current price and the sell price adjusts upward as the stock price goes up. For instance, today GS was up to $105/share. So I entered a 5% trailing stop meaning if it goes down 5%, I will sell (basically at $100). However if the price were to go up to $110, the new sell price would be 95% of that, $104.50. If it goes up steadily forever, I will never sell. But if it goes down 5% at any time, the shares will sell. They could sell tomorrow.

What’s worse, if the stock market futures go down tomorrow morning before the market opens, Goldman Sachs might open at $90/share and, because that is at least 5% below my target price, the shares will be sold instantly at $90.

So there is risk all over the place. First, there is a risk the stop could trigger below my set price. Second, there could be a 5% blip downwards tomorrow before the stock goes back up again, and I would have sold and missed the rebound. Third, I could have sold the stock today at $105 and been done with it. So if the stock sells below $105, then I haven’t really gained anything at all by using a trailing stop. If I can somehow beat that price, then I might become a fan of trailing stops.

If the price goes up another $10 or so, I could change to a 10% trailing stop so that the shares wouldn’t sell on a volatile day.

I’ll let you know how this works out.


A couple of years ago I rented a neat movie from Netflix called Koyaanisqatsi. It is a collection of video footage set to music by Philip Glass (who also wrote Akhnaten which I wrote about in January). There are no words, just a series of video footage of various things, often time lapsed or slow-motion, (rockets, traffic, clouds, factories) set to different instrumental pieces. When I was at the library once last year, I saw the soundtrack was available to be checked out, so I took it home. It’s classic Glass, very repetitive, great music to set a mood. Since doing that movie in the early 80’s, Glass has done a number of other soundtracks for movies including The Truman Show, The Hours, The Illusionist, and Kundun.

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