After the circuit design comes the hard part, the board layout. I went through several iterations of trying to fit all of the different components on the board but essentially based the design around the Bluetooth module, which I knew I wanted on top, the screen header, which I wanted on the bottom, and the buttons which I wanted on the right side of the watch. Below is the fruit of many hours of labor. The board design is actually the stage which decided the final components I would use. During the circuit design phase I had included an RTC and crystal oscillator, but as you can see below, there wasn’t really any room for it. I also figured that the internal oscillator on the AVR is reasonably accurate and the time could be included in a data packet sent from the phone.
The top layer of the board is a 3.3V pour and the bottom is a ground pour, but after adding all of the components to the board I noticed that the power would have to take a rather circuitous route to reach some of the components on the right side. To remedy this, I decided to add some last minute capacitors and shift some components around to provide better connectivity. However, in my rush I ended up making a few minor mistakes. Namely I placed several capacitors and components directly under the Bluetooth board.
And here are the fabbed boards! I ordered them from Fusion PCB since they are the cheapest option I could find and provided a quantity of ten boards in the event I made a lot of soldering mistakes. I only glanced at a few of the boards but am very satisfied with the quality. The only downside of their service is the turnaround time. It took twenty days from day of order to day of delivery, which is reasonable since they’re based in China, but can be frustrating if you need to make multiple iterations and improvements.