Peter Fearey

Electronics Design

Assignment

Redraw the echo hello-world board, add (at least) a button and LED (with current-limiting resistor), check the design rules, and make it.

Ideas and Approach

I decided to make a board that would be quite versatile.  I wanted to make it so that I could exchange inputs and outputs to test certain components.  To that end, I wanted to have 2 2x2 headers (one for inputs and one for outputs).  And with each of these headers, I wanted to have one analog and one digital "port".  That way I could easily attach new components and test.  I am ultimately hoping that this is something I can use to teach students how all this works using simple connections (e.g. just connecting a component to a header). 

Design Files

• Here are the Eagle files I used for the final board (board   /   schematic)
• Here are jpgs of the board cutouts (traces / perimeter)
  

Steps Taken

On the Thursday night after the class, I headed down to AS220 where Shawn (our awesome TA), gave us a great rundown of electronics/electrical components. 

		Here's my first draft after leaving AS220.  After not thinking about it for a day and a half, I went back and reviewed what I had.  I realized I had a few things that were wrong or could be better... 1) There were some traces I realized would be near impossible to solder.  For example, the following connections/traces wouldn't really work because they had interior connections that I wouldn't be able to solder... pin 9 of the ATtiny pin 4 of the 2x3 jumper. pin 3 of the ...wait...now I feel like an idiot.  I am wrong.  The big areas are the pads that will be soldering to so it doesn't matter what side of the pad the trace comes in on.  Doh... 2) I realized I should label some parts so that I'd know what they are when attaching things later on.  For example, I should mark which jumpers are for each pin. 3) I realized there might be some places that I could add more space to make the soldering a bit easier (e.g. the crystal & ATtiny are REALLY close).  I realize the crystal needs to be close, but I can move it a small amount to the left.  4) I decided I want to add a second 2x2 header for outputs (one analog and one digital).
		1) I did the pull up resistor wrong.  In general each Analog input needs a +5 (for pullup), GND and Signal value when doing the header. 2) My R3 resistor wasn't doing anything of value so I changed it from 1K to 0K ohms (thanks to Shawn for explaining this). 3) I found I was wrong about labeling.  It turns out you don't want the labels.  It messes up the traces if the words go across the board.  Obvious when you go to mill the board and you see the pictures.  4) My regulator/capacitor connection was wrong.  I through it was supposed to sit in serial in between the regulator and +5V.  That's wrong.  It is actually supposed to be in parallel.

Once I had the board design, I milled out the board and stuffed it.  Here was the final result.  I felt much better about this one because I ended up getting it right the first time.  No jumpers.  No big mistakes.  And when I plugged it into the programmer...yeah!...I was able to burn the bootloader.