How To Make

Week 5: Circuit Design

We had to design a hello world board (blink LED). The main goal is to learn to do circuit layout. I used Eagle although KiCAD was tempting.

In a break from previous weeks, instead of writing a journal, I will create checklists as I am going along. Will be easier for you

First draw on paper
Use standard/LED library to get LED
Use standard/supply1.lbr library to get VCC, GND
Rest of the part from fab.lbr
Use named nets for readability
keep conceptually separate circuits separate in the schematic (eg. don't wire switch and led circuit together) (from Jeff D)

Drawing traces should be newspaper puzzles.
Rotating a component in Eagle is not obvious. Click to select and then right click. (right click without selecting opens a context menu)
First lay everything out with a lot of space and then shrink
protip: to check if you are done, hit ratsnest to see if there are any airwires left
Avoid right angle traces (from Jeff D). Can reflect high frequency signal. Also bad mechanically.

Redraw the dimension layer using wire so it snug around the board
Drag the fainter gray outline (board dimension) so it it is close to the dimension outline
In the command bar: display none top shows only the traces
display top tNames dimension tPlace tDocu gives traces, name, outline and placement + component outline
Use display none top and then export PNG with 600 dpi for traces
display none dimension and then export PNG with 600 dpi for outline cut
Use gimp to invert and fill out the outline cut image so it is white on the outside all the way to the edge and black in the middle
You can also use gimp for adding some flare to the image. I just added round corners because.

On Roland Modela

put in view mode
tape down FR1 board on top of sacrificial layer
change end mill to 1/64 for traces 1/32 for outline
unscrew two screws on the shank
chnage mill
zero end mill
use move to xmin, ymin to get to a corner of the board
lower end mill with up / down button on modela until it is close to the board
unscrew end mill
hold end mill in hand and lower head a bit more (shank will spin while you hold end mill)
lower end mill by hand and it touches the board
hold it down while you screw the two screws back in
this is now 0 Z

On the computer

make sure mod_server is running
make sure settings for talking to modela is correct (on modela-1 ttyS0 9600 rts cts)
calculate path
verify path by inspection
hit send

After I milled a board I found out that the bit must have been dull. produced a board with furry traces
Fab modules errored out with WebGL not supported. As a work around, I used a different computer to compute the tool path and then copied over the rml file and ran mod_serial.py from command line to push the path to the tool. Advice from mike: clear cache

The flow control for the serial communication to the mill wasn't set correctly (rtscts) which sometimes caused the millhead to wander off and kill the board
Picked the wrong registers for soldering. cf register codes