Building a LED Flasher in Eagle

1. Starting Eagle

Open Eagle. Goto File>New>Schematic. (see below)

2. Getting the Required Parts

In the toolbar on the left click the Add button. This opens up the parts library

which contains the symbols for all the various parts you can add. Parts are grouped

into libraries of similar parts. The LED flasher uses two surface mount transistors so

type transistor in the search box and hit enter.

Packages: When you select a part the left window will show you what the part will look

like in your schematic and the right window will show you the package. The package

can be thought of as the footprint of the part. It tells Eagle where to put the pads

when you create the actual board layout.

We are using a npn transistor with a SOT23 package. With the part selected hit ok.

The Add window will close and you will be back in the schematic window. A bright red

transistor should now be attached to your mouse. Left click to drop a transistor in the

schematic, when you drop it should turn dark red, this tells you that it has been added

to the schematic. After dropping the first transistor notice that there is still a bright

red transistor attached to the mouse. We need two transistors so left click to place

another one in the schematic.

With the transistors placed click on the Stop button to tell eagle you want to stop

placing parts. You must click Stop after you finish with an operation such as adding,

moving, or copying a part otherwise the next time you click on a part Eagle will

assume you are still performing that operation.

Next place two LEDs. We are using surface mount LEDs with 1206 package.

After placing the LEDs place the following parts.

2x surface mount capacitors (search CPOL-EU153CLV-1012)

4x surface mount resistors (search R-US_R1206)

1x 2 wire jumper (search JP1E)

Make sure you have all the parts in the image below.

3. Moving, and Labeling Parts

Now that we have all the parts we need to rearrange them so they are easy to connect.

To move a part click the Move button and click on the part you wish to move.

When you click on a part it will turn bright red and become attached to your mouse.

Right clicking will rotate the part and left clicking will drop the part. Move the parts so

they match the image below.

Note: In order to make the both transistors face the right way you need to mirror one.

Click the Mirror button and then click on the transistor. Don’t forget to hit Stop

after you are finished mirroring the part.

All of our parts are now laid out but none of them have labels to tell us what their

values are. To label the value of a part right click it and select value from the menu.

Label the remaining parts to match the image below.

Connecting the Parts

We now need to actually connect up all of the components. We do this using the Net

tool. The Net tool tells Eagle which nodes are connected. The net is not the

physical wire we create those latter.

Note: It is important to remember that this is only a schematic. How we wire and place

the components here will not necessarily be how the wires are laid out on the actual

circuit board.

Use the Net tool to wire the components together.

Creating the Board and Arranging Parts

Now that we have completed the schematic we need to create the actual circuit board

layout. Click the Board button. Eagle will send you a warning telling you that it

doesn’t have a board file for your schematic and will ask if you want to create one,

click yes.

Eagle will open up a new window with a blank area with all your parts in a corner next

to a white outline.

Your parts are now represented by their package and are connect to each other with

yellow lines. The yellow lines are called “air wires” and represent which pads are

connected via the nets we made earlier.

Using the Move tool place all of your parts inside the frame. The fewer air wires

that cross the better. You can use the Ratnest tool to have eagle redraw the air

wires to the shortest distance. I found the below layout to work fairly well. You can

experiment with your own layouts just keep in mind that the smaller the board the

faster it can be cut out so try to keep things compact.

Note: If one of your parts turns blue it has been moved to the bottom side of the

board. We can only use one side so make sure everything is red.

Routing the Traces

With the parts placed we want to route the actual traces. Save your board file first. If

something goes wrong in this step it is easiest to revert to a previous save then trying to

undo everything.

With your parts laid out hit the Autorouter button. This opens up the autorouter setup

window. The “Preferred Directions” option changes what type of traces it will try to use. I

like using nice straight traces with few diagonals so I chose “|”. Since we only want traces on

the top of the board set “Bottom” to “N/A”.

With those setting chosen click ok. Eagle might cycle through a couple different traces as it

tries to find a good match. My end board ended up looking like the one below. With that you

are ready to cut out your board on the Modela.

Fixing Problem Spots

It is possible to route traces in areas where the Modela can not cut them out. For instance in

the circuit below there is not enough room between the pads and the trace for the cutting

tool. In order to make sure the Modela can cut out all the traces avoid running traces under

transistors or next to pads.

The drill needs enough room to travel along the green lines.

You can manually route traces using the Ripup tool and the Route tool. While using

Route tool you can right click to change what style traces to use. For best results use

straight traces whenever possible. If you are having trouble laying out the traces you can add

vias or a 0 ohm resistor to the schematic to act as a jumper.

Using vias as a jumper.