Electronics Production

This week's assignment was to mill, solder, and program a FabISP circuit board. The FabISP is an in system programmer for AVR microcontrollers, specifically designed for fab labs. It uses a USB cable and a 6 pin IDC to 6 pin IDC cable to communicate. With this, the ATTiny can communicate with Serial Software. Our first step was to use Eagle, a free program you can use to design your own circuit board. It stands for Easily Applicable Graphical Layout Editor. It can be a bit tricky for beginners. There are lots of icons to explore. The first thing we did in Eagle was to download the fab libraries so we could find the right components. Fist you lay out a schematic, and then you move on to the board design. There are many ways to route your board. I used the auto router a few times to see what it would come up with. Then it was time to mill the boards!

After a few adjustments, we learned how to prep the FR4 board. The FR4 stands for a mix of epoxy, resin, and fiberglass. The "RF4" stands for flame retardant. We used doubled sided tape to secure FR4 board to the medium-density fibreboard, which was also taped down to milling surface. This MDF wood would allow us to cut all the way through the FR4 board, and not damage the Modela's plate. We also learned how to change the drill bit. It is important to keep pressure on the bit while tightening, so that it stays in place. Over tightening can cause the bit to shift. Pressing the view button allowed us to get the drill into place. We then sent the rml file to the modela and watched the drilling process.

It is best to have a mini vacuum to keep milling surface free of shavings. A can of air will also suffice. Once the board was milled, we cleaned it, and placed a vinyl sticker stencil we made using the Silhouette. Clear contact paper allowed us to place the sticker over the tiny rectangles of the board accurately. It helps to double side tape the board down when placing the stencil. Solder paste was then scraped onto the board evenly. When peeling off the sticker, it is best to pull gently and slowly. Placing the electrical components is tricky. We placed the microcontroller first, so that pin 1 was lined up. It takes a steady hand and a good pair of tweezers. We saved the headers for last. Then we baked it in the oven! It took about 2 minutes at 475 degrees for the all of the solder to turn shiny. Once it did, we carefully removed the board and let cool before checking it over.

I enjoyed placing the components, so I placed the parts for a second circuit board, and baked that one too. They both turned out successful! Then we had to solder the jumpers before programming. When programming went well, we desoldered the jumpers so that the newly programmed circuit board could be used to program the next one. Making the cables was the easiest part.