Week 6: Electronics Design

For this week, I had to design a PCB with an attiny44 microcontroller and a few other components. I designed the schematic and board using Eagle, exported the design as png file, and milled a copper board using the Modela milling machine.

Schematic

As suggested by Jeff (TA for this week), I always kept my schematic design within a frame. The design was straightforward, using named nets to connect the components instead of wiring them up. In my my first trial I forgot to use named nets. I wired up all the components, and the schematic was messy. It also produced some connections in the board that I could not trace. So, I was forced to follow the much cleaner procedure -- named nets.

Routing

This was arguably the hardest and most time consuming part. I tried to route the nets manually, and spent a lot of time fixing many routes. However, a few crossovers could not be avoided. Then I tried the Autoroute option. This seemed to work, mostly. When autorouting, make sure that one of the layers (say, the bottom layer) is selected as 'N/A'. I fixed the unrouted wires manually. For one of the connections, I had to add a 0 ohm resistor as a jumper. By manually moving the routes a little farther from each other, I was able to create more space between them.

Design Rule Check

The default .dru file in the fab library had to be changed a little to account for the drill size of the Modela. With the modified .dru file, my board layout mostly passed. The font had to be converted to a vector font, with "persistent for this design" option checked.

PNG Output

By selecting the top layer and dimension layer at a time, I exported two PNG outputs at 600 dpi resolution. The border was modified with the 'Move' tool to change the shape a little.

Other Attempts

I also added a Carbon Dioxide sensor (MQ2) in the board. However, even though the routing attempts were quite successful, the layout wouldn't pass the design rule check, because of too many routes going through constricted paths. I eventually gave up on that effort.