Using Eagle PCB you can make a computer drawn schematic diagram of your circuit. With this schematic you can generate a board file. The board file can be printed or sent directly to a mill using G Code.
This page will bring you through the steps of making the schematic diagram for a very simple circuit. There are some fine tutorials on Eagle, but they seem to require you to know kind of a lot to get full use out of them. This is written for the experimenter who has never used the software and has only basic knowledge of electric circuits. If you want to know more, there are plenty of good resources out there.
First choose a circuit. Draw or get a copy of the schematic diagram. Your circuit should be pretty easy to read until you get real good at the software side. Using a simple circuit will also help you if you need to troubleshoot any problems you encounter.
This circuit will be a darlington amplifier night light. It will cause a light or LED to illuminate when it gets dark.
Open Eagle and choose NEW -> Schematic
Next you should check out the tools in the toolbar. You can hover your mouse over them and a window will pop up with the name of each tool. Do this for each tool, so when you need something, you might be able to find it relatively quickly. Some of the tool names may not make sense at first. Maybe you need them, maybe not.
We are going to need some parts: LED, 9 volt battery, 4.7k ohm resistor, 100 ohm resistor, two 2n3906 transistors, a cds or photocell
To find parts, choose the Add tool, usually it will be on the left about midway down. It has a nand schematic with an arrow pointing to it. Click on the tool.
A window should pop up with a couple of features: On the left is a laundry list of parts libraries, then there are two panes on the right that will show images of the part. Below is a long search field. If you are not using SMD or Surface Mount Devices, unclick that item from the search. Put the name of the part you want in the search and hit the enter button. You should get a long list of parts. Using partial names doesn't always work, try to use the full name of the part. Putting in LED will give a bunch of LED segmented displays up top, then way down the list is LED. click on the words and you should see the board and schematic symbol in the panes on the right. When you find one that is the right size for what you intend to use, select it or double click on it.
This should bring you back to the schematic window. The cursor should be showing the symbol of your part. If you right click on the mouse it should rotate the part image. Get it to show the way you want to use it in the circuit, then left click to place it.
Add another part image for the battery. We are using a 9volt battery, so Add part, search for battery and get a symbol for a battery. Rotate it so it matches your reference schematic.
Now you have two parts. You will need to connect them to begin to make the circuit. Choose the WIRE tool, down on the left. Looks like a diagonal line. Add the wire from the negative end of your battery to the negative lead of the LED. You should be able to connect them by left clicking the wire just on the end of the component, then moving the mouse to the side to connect it to the LED.
Once you have the wire in place, switch tools to the MOVE tool. Left click on each of the components. The component and wire should both move when you move one. If the component moves but not the wire, then you don't have a connection. Keep trying to get the wire on until you can do it consistently. If you zoom way in on the junction, you should be able to see where the color of the wire overlaps the color of the component.
Add the next component, a resistor. ADD component, search resistor. There are European components and US components. Go with what works. Add it right to the positive lead of the LED. Check it to see if the parts are connected by moving the Resistor.
Add two 2n3906 pnp transistors. Wire them into the negative end of the circuit with the resistor and LED. Click on the part with the MOVE tool and the part and its connecting wire should go clear. This seems to show that you have a connection.
Ok, you need another resistor, but you are too lazy to go search for it. Click on the COPY tool, then select the existing resistor. You should see that the cursor now has a resistor attached to it. Bring it over and attach it to Q1, one of the transistors.
Here is the file:
