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.

I was able to create the Gerber files by following the Hackaday instructions, plus further instructions they referenced about using a CAM file at Sparkfun to create the right format of Gerber files.

Once the Gerber files were made, Hackaday recommended checking the Gerber files in a Gerber viewer. There is a free one called Viewplot, so I downloaded it, and as far as I could tell, it seemed to look okay.

With the Gerber files created and checked, I went to the same company Ladyada had used, Advanced Circuits, and found out I needed to put the files in a zip archive first. I didn’t have a zip program on my computer so I tried to download Winzip, which we have at work, but you are supposed to pay for it, so I wound up with FreeZip. I uploaded the zipped archive of files to FreeDFM which is run by Advanced Circuits to check the circuit for problems. It didn’t recognize the file extensions, so I had to tell it which file was for what (one file is for the holes that need to be drilled in the board, plus separate files for the top layer and bottom layer that trace the wires, the solder pads, and the writing, 7 files in all). I think I should have stuck with the built-in CAM files of Eagle. I also had to fill in values for about 20 different parameters of the circuit board like material, colors, tolerances, etc. I tried to use defaults plus Ladyada’s web page had an image of her price quote that had most of the parameters listed. It then generated a report saying I had a ton of errors relating to width of silkscreen print (doesn’t seem like a big deal) and my wire paths (could be a big deal), but the software automatically corrected everything.

The checking software also generated a quote for how much it would cost to generate different numbers of boards. I could get 150 boards for $3.79 each ($568.50). I figured I would need to order some extras in case I messed some up. The next lowest choice was 50 boards for $10.82 each ($541.00, only $27 less). Ladyada’s writeup said that the quote did not include a $150 price for setting up the production run, a one-time fee that would not apply to subsequent orders of the same board. But I think the price now does include that because it said the setup fee was $0.00.

What would be really helpful is if I could take Ladyada’s setup at this company and re-order 120 boards (or 60 if she has 2 boards per piece). Then I would know that it would work (wouldn’t have to go through all of this business of creating and uploading Gerber files) and wouldn’t have to pay a setup fee again. I left a message on Ladyada’s message boards to see if I can get the v1.2 board design and she said that she didn’t have the design files and suggested I recreate the Gerber files.

Anyway, the end result is I feel somewhat confident that I could order the circuit boards for v1.1 and I told the guy I could do it. Whether the boards would really work (did I have the right version of the board design file, did I create Gerbers correctly, did I choose all the right parameters?) and whether they would be cut to the right size (Ladyada’s came from the factory with the rounded corners) would be another issue.

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