For this week's assignment, I made the FabISP in-circuit programmer by milling out the printed circuit board (PCB) and stuffing the board with components. The traces and the outline image files were given and I used machine shop on the first floor of Media Lab to mill the board, using FabModules. Input file was .png file, output as .rml (Roland mill) and I chose PCB traces (1/64) for the process. First, I put three strips of double-sided tape at the bottom of the board to make sure the board would not move during the milling process. The cut depth parameter was set to 0.13mm and I used 1/64 end mill to trace out the board. The cutout offset was set to 4. I modified the xmin and ymin parameters to position the endmill to the appropriate position before sending the tracing job to the milling machine.
PCB trace image and the milling process
After the tracing job was finished, I used the 1/32 end mill to cut out the outline. The input and output for FabModules were set appropriately and PCB outline (1/32) was chosen for the process. I replaced 1/64 endmill to 1/32 endmill on the machine. The cut depth parameter was set as 0.6 mm by default and I could see there were three traces on vertical side. I took out the board and washed it with soap and water to get rid of any residue and scraped the surface with the ruler.
Printed Circuit Board (PCB)
Then I stuffed the boards by soldering components on the PCB. I put a tiny bit of solder on one connection part of the component and used it as a glue to stick the component. Once the component is fixated on the appropriate place, I soldered the other connecting part and modified the other connecting part. I soldered small parts that were place inside the PCB first to make sure big components on the edge will not be blocking the way when soldering other parts. I made sure the orientation for the diodes and the micro-controller was correct. For diodes, there was a small vertical line on the component that indicated the C polarity in the diagram.
After the board was stuffed, I programmed it with AVR programmer and desoldered the short jumpers.