Week 6

Assignments:

redraw the echo hello-world board

add a button and LED (with current-limiting resistor)

check the design rules, make it, and test it

Redrawing the Echo Hello-World Board

After a comprehensive review of principles of electronics design in Eagle with the local Fab Lab expert Dorina, I installed and used the software on my laptop.

To complete this week's assignment, I used tutorials provided by Dorina and FabAcademy. I started with downloading and insalling component libraries. Library fab.lbr is located in the Electronics design Fab Academy page. It has to be saved in the Eagle local folder (e.g. on Windows C:\EAGLE-7.5.0\lbr or on Mac /Applications/EAGLE-7.5.0/lbr).

This library contains all the components needed to design and produce the board. To install the library in Eagle, go to the top toolbar and select the Library menu then select Use.

After that, I redraw the echo hello-world schematic. To work with the Eagle interface, I used Graphical Icons Toolbar. Here are the components used and libraries where they are located.

Component	Name	Library
6-pin programming header	PINHD-2X3-SMD	fab
attiny44A microcontroller	ATTINY44-SSU	fab
FTDI header	FTDI-SMD-HEADER	fab
20MHz resonator	RESONATOR	fab
capacitor	CAP-US	fab
pull-up resistor (10k)	RES-US	fab
ground	GND	supply1
VCC	VCC	supply1

To add components: Add button on the Toolbar - fab OR supply1 - choose a component - OK

After that, components need to be connected. In order to avoid net crossovers, I used an option to connect componens by giving the connecting nets identical names.

In schematic, I also used buttons

Net to make logical connections

Junction to add junctions

Value to add values to components (i.e. ohm rating)

Name to name components

Label to display names components in schematic view

Adding a button and LED with current-limiting resistor

The next step is adding

Component	Name	Library
button (OMERON switch)	6MM_SWITCH6MM_SWITCH	fab
green LED	LEDFAB1206	fab
current-limiting resistor (499 ohms)	RES-US	fab

I used ERC, the electronic rules check in schematic view to ensure that the board will work.

Then I switched to the Board Layout to route traces on the board.

To finalize layout in the board view, I used buttons

Move to move individual components and wires.

Route to route each traces. The wire will turn red as you route it into place.

Autorouter - I tried this feature, but ended up editing most of the created traces traces manually.

Ratsnest to detect airwires

Checking the design rules, making and testing

I used DRC, the design rules check in board view to ensure my layout is error-free. Initially, I had

Clearance errors due to having routes too close to the components

Dimensions errors due to going outside the board boundary

To fix the errors, I

Set Clearance in DRC

Changed the dimension of the grid in View - Grid

Changed the width of the wires with Change button - Width

I ended up with the following schematic and board view layouts

Next, I exported the top layer design from Eagle to monochrome 1500 dpi .png

View - Layer settings - None

1: Top (to selecting only the top layer of the layout)

File - Export - Image

As recommendered by local insttuctors, I used Gimp and to create traces and cutout for milling. I followed Dorina's instructions:

1. Open the image in Gimp and create a new layer with foreground color black.
2. Set Layer Boundary Size for the outline layer by adding 1.6 mm to width and height centered. This is the margin milled away by the machine with the 1/32 bit (2.54 inch/32 = 0.8 mm).
3. Change the order of the layers in the Layers tab: on top the traces layer, and below the outline layer.
4. Enlarge the image to fit all layers: Image - Fit canvas to layers. Then fill the empty area with black.
5. To create the traces image file, export the image as .png.
6. To create the cutout image file, fill the traces layer with white and export the obtained image as .png.
7. These two files (traces.png and cutout.png) will be used in Fab modules (fabmodules.org) to create the .rml files used by the milling machine Roland SRM-20.

I generated the following files.

Cutout
Traces

Next, following the same instrucions, I created the milling files (cutout test, traces and cutout) in Fabmodules for the Roland SRM-20 machine. The steps were the following:

• At http://fabmodules.org, select input format - image (.png)
• Select the file to process (e.g. traces.png or cutout.png)
• Select as output format Roland mill (.rml)
• For creating the traces .rml file:
• Select as process PCB traces (1/64).
• In the right-hand column change the parameters: x,y,z = 0
• The other parameters remain with the default values
• Calculate to obtain the milling paths
• Save to save the .rml file
• For creating the cutout .rml file:
• Select as process PCB outline (1/32)
• In the right-hand column change the parameters: x,y,z = 0
• The other parameters remain with the default values
• Calculate to obtain the milling paths
• Save to save the .rml file.

I had to do milling twice, since the first attempt failed.

Fail: an issue of the milling bit? Pass :)

Next, components are collected and soldering started...

Soldering done Checking LED connections Checking button connections

Files:

Echo hello-world with LED and button .sch and .brd files; cutout and traces .png files; cutout test, cutout and tracel .rml files

Remember, remember...

• Working in Eagle, don't close layout and not schematic (or vice versa) - you need to keep both open all the time! Closing one view while the other view is open (and making edits) will break the link between the two
• Check and correct errors found ERC and DRC in Eagle
• Find a right resistor for the light
• Make sure components are in the right direction before you start solding