# Kim Smith

## Electronics Design

### Designing with Eagle

I thought this would be easier than it wasâ€¦ first a super helpful recitation about electronics.

Basic equations:
• V=IR
• Kirchhoff's current law (KCL): The sum of currents in a network of conductors meeting at a point is zero.
Started with a set of parts and an existing board, the hello world board and asked to add some things, a switch and an LED. Much of the week felt like wandering around in the dark. Looked up all the parts to determine their features and values. Looked at the original board, read through othersâ€™ pages, and started with Eagle. First in Eagle, had to load the fab library of parts. Copy the .lbr into the directory, under library, or open up the library tab. From here, most of the parts we would be using are dropped in and easy to find.

I started adding pieces onto a schematic in Eagle.
Edit--Add--then look up the part under the Fab library. Some things were more mysterious, such as ground (GND) and voltage (VCC)...they were in the Supply1 library in Eagle.
Parts:
• fab/attiny44-ssu
• fab/res-us1206fab
• supply1/+5V
• supply1/gnd
• fab/resonator
• led/ledsmt1206
After I dropped the parts, I loosely arranged them so that the orientation seemed efficient to wire the pieces. From there, I connected the pins and components. In order to connect wires in Eagle, use the Net key (not the wire key) to draw wires from parts/pins. Draw a short line, label it, assign a value. When two wires are labeled with the same label, Eagle will prompt to connect them. After everything was connected, I opened up the Board view.

First placed the pieces on the boundary of the board and roughly tried to place them in an efficient orientation. Right click to rotate. From here is was a long confusing puzzle. But was fun. Trying to get the wires the most direct route, not crossing...I had some difficulty keeping it straight when I tried to clean up my initial design. I left my design bigger than it should have been. I realized later that it was even too wide for the copper plate. So, I shrunk it down to fit comfortably, although it probably could have been much more compact. In one spot I could not figure out how to route without crossing, so I inserted a zero ohm resistor to jump over. After I was happy with the layout, I hid extra layers so that only the routes and part footprints were visible. I exported to png file, saving it at 600dpi, in monochrome.

### Milling

This process was the same as last time and this time it went very smoothly. I first loaded the settings and then walked through the fab module to set up the png for milling. I had some difficulty maintaining the connection between the computer and the Modela, which happened last time and I still am not sure how to trouble shoot that one. I managed to cut the board in one try with the traces; however, I had something wrong on the outline, because the first try didn't cut through the outline. I had drawn my outline in Photoshop, after having some difficulty getting a wide enough boundary in Eagle. I changed some settings, rebooted it all, and then cut again. It came out beautifully.

### Stuffing

Again, this step was easier the second time around. I started by gathering all the parts and laying them out. Keeping organized and clean makes this part easier. Soldering was easier, but I am still struggling with getting the solder and flux the right temperatures to flow well. My joints looked cloudy after several tries...But, it came together.

PCB Schematic
PCB Board