This weeks assignment was to add a button and an LED to the Hello Echo board. Mill the board, stuff it and program it. I was working on a machine in the lab so I didn't need to download the software or the libraries. I opened the Hello Echo schematic in Eagle. Following the Fab Academy tutorial I added the 2 10k resistors from the ng library, the LED from the FAB_Hello library, the button from the fab library, added the grounds and the VCC. Next I added wires, or nets as they call them in Eagle, to connect the LED to the pull up resistor and ground. I also connected the button to ground, the resistor and VCC. I named the LED net "LED" and the button net "BUTTON". Then I named pin 6 on the microcontroller "LED" and pin 10 "BUTTON". This makes the physical connection between the microcontroller and the component of the same name without drawring a connection in the diagram. After making all the connections I ran the Electrical Rules Check and everything was A-OK.
The next step was to route the traces in the board view. I switched to the board view and started placing the new components onto the board. I used the diagram from the tutorial as a guide and everything went pretty smoothly. I had a few funky looking traces that I had to clean up but no big deal.
The next step was prepping the board to mill. I exported the traces as a monochrome 500 DPI png file. Then I opened the exported file in The Gimp and added a 20 px white border around the image. I flattened the image and saved it as helloechotraces.png. Then I saved it as helloechointerior.png and edited out all the traces to create the file to cut out the board. With my board files finished I mounted a board to the mill and ran my helloechotraces.png file.
Then wait, wait, wait. With traces all cut I ran the helloechointerior.png and viola a shiny new PCB ready for stuffing.
For this project I decided to use solder paste to attach my components
instead of using a soldering iron. To start I used a flux pen to apply flux to all of my solder pads. Next I used a small knife blade to apply a small amount of solder paste to all the pads that needed to be soldered. Once the paste was applied I carefully placed all of the components except the six pin header on the board. Because of the shape of the six pin FTDI header I could not put it on the board with the paste. I then baked my board in the toaster oven at about 350 degrees. After several minutes the solder paste had not reflowed. Afraid that I was going to over cook the components on the board I bumped the temp up to around 400 degrees. A couple minutes later the paste reflowed. I took the board out and let it cool. I had a couple of spots on the board where the copper hed started to bubble and the board itself was slightly toasted. Next time I think I will preheat the oven with the baking tray in it to try and reduce my cooking time. Hopefully this will speed up the reflow time and reduce the damage to the board. Once my board cooled, I hand soldered the FTDI header onto the board.
