assignment 4: pcb design
  • assignment
    • add a button and LED to last week's hello world circuit, then machine and stuff another board.
  • using cad.py

    • I used cad.py to create a new board layout because I thought programming the connections would be easier than learning how to use a complex circuit design package like Eagle. I had used Protel once for a more complicated circuit project, and liked its "auto-route" feature that would automatically translate a schematic into a printed circuit board, but I remember it being very difficult to set up. So I thought it would be easier to use cad.py. However, I made an assumption about the layout of the switch that cost me a lot of time. Even though I had created a schematic drawing on paper (pictured later on this page), I didn't translate it correctly when I was laying out my board. I didn't discover the problem until I was soldering my board, when I noticed that I hadn't connected the left and right sides of the switch. As a result, I was shorting out one of the pins on the ATTiny45.

      Using cad.py made printing the completed board pretty straight forward. Setting up the connections would have been easier if it were easier to figure out which "pads" on the elements were which without having to read lots of Python code.

  • using the modela

    • I followed Stephen's instructions as I did with last week's assignment, but had less success than I did last week. I think that the first time I tried to cut the board, the drill bit was dirty and didn't cut deep enough. Caitlin and Simon had been working on their boards before me and recommended changing the cutting depth to 7mm instead of 5mm, which worked much better. I also got overly worried about making the bit too tight, and ended up not getting it in tight enough -- it actually fell out while I was cutting out the board!

  • circuit design
    • I drew a circuit diagram on paper before starting to design the board (note it does not include the complete circuit for the serial port and programmer):

      I went to one of Amy's tutorial sessions to get a little advice on designing the board, and she was very helpful.

  • board design

    • This is my board design:

      If I were to design the board again I think I wouldn't put the button so close to other, taller components so that it would be easier to press.

  • results

    • Another tiny circuit board:

      It's not too much bigger than the original: