Making Printed Circuit Boards with the Fab Lab

Marc Boon, Feb 2008

Step 1. Creating a PCB layout in Eagle

If you never used Eagle before, first read the manual and the tutorial!

The schematic of the Micro Silent TV transmitter as entered in Eagle looks like this:Micro TV Schematic

Once your schematic is complete and error free (use the menu command Tools | Erc.. to verify this), you are ready to design the pcb layout. Switch to board layout and first define the board dimensions (consult the manual or tutorial if you don't know how). The Micro Silent TV transmitter fits nicely on a board 1.9 inches square. Using a grid setting of 0.05 inch helps in placing the components.

We will design a single-sided layout, with components on the top side, and copper traces on the bottom. The components are mounted on the top side, and soldered on the bottom side.

To make sure the board can be fabricated with the Roland Modela milling machine, we will use a set of design rules, which specify the layers used (bottom layer only), the minimum distances between pads and traces, diameters of holes, width of copper traces etc. Open the Design Rules dialog with the menu command Tools | Drc.. and load this file using the Load.. button.

With the design rules loaded, layout the pcb traces, either manually, or with the help of Eagle's auto-router. When the layout is complete, verify it using the menu command Tools | Drc.. | Check.

There might be some warnings about pad clearance. The default TO92 package for the transistor BC337 has a pad spacing that does not comply with our design rules. To fix this, we need to specify a different package. Eagle's library transistor-npn.lbr only specifies one package for this part, but you can use this modified library and select the alternative package TO92L, which has a larger pad spacing.

After applying the design rules, the trace widths, pad diameters and hole sizes will be adjusted according to these rules, ensuring it can be fabricated with the Fab Lab milling machine.

The finished layout should look similar to this:Micro TV layout

Now, continue with Step 2: Creating a toolpath for milling and drilling.

Back to start.