The schematic editor allows you to create a symbolic easy-to-read representation of your
design. The goal of the schematic is to provide documentation about the design, allowing
others to easily understand your design intent. EAGLE comes with thousands of pre-made
parts that simplify your schematic capture tasks. The ERC functionality checks that you have
defined all of your connections properly.
PCB design in EAGLE is a two-step process. First you design your schematic, then you lay out a PCB based on that schematic. EAGLE’s board and schematic editors work hand-in-hand. A well-designed schematic is critical to the overall PCB design process. It will help you catch errors before the board is fabricated, and it’ll help you debug a board when something doesn’t work.
This tutorial is the first of a two-part Using EAGLE series, and it’s devoted entirely to the schematic-designing side of EAGLE. In part 2, Using EAGLE: Board Layout, we’ll use the schematic designed in this tutorial as the basis for our example board layout.
Create a Project
We’ll start by making a new project folder for our design. In the control panel, under the “Projects” tree, right click on the directory where you want the project to live (by default EAGLE creates an “eagle” directory in your home folder), and select “New Project”.Give the newly created, red project folder a descriptive name. How about “Bare Bones Arduino”.
Project folders are like any regular file system folder, except they contain a file named “eagle.epf”. The EPF file links your schematic and board design together, and also stores any settings you may have set especially for the project.
Create a Schematic
The project folder will house both our schematic and board design files (and eventually our gerber files too). To begin the design process, we need to lay out a schematic.To add a schematic to a project folder, right-click the folder, hover over “New” and select “Schematic”.
Adding Parts to a Schematic
Schematic design is a two step process. First you have to add all of the parts to the schematic sheet, then those parts need to be wired together. You can intermix the steps – add a few parts, wire a few parts, then add some more – but since we already have a reference design we’ll just add everything in one swoop.
Using the ADD Tool
The ADD tool – (on the left toolbar, or under the Edit menu) – is what you’ll use to place every single component on the schematic. The ADD tool opens up a library navigator, where you can expand specific libraries and look at the parts it holds. With a part selected on the left side, the view on the right half should update to show both the schematic symbol of the part and its package.
Step 1: Add a Frame
The frame isn’t a critical component for what will be the final PCB layout, but it keeps your schematic looking clean and organized. The frame we want should be in the SparkFun-Aesthetics library, and it’s named FRAME-LETTER. Find that by either searching or navigating and add it to your schematic.
Step 2: Save (And Save Often)
Right now your schematic is an untitled temporary file living in your computer’s ether. To save either go to File > Save, or just click the blue floppy disk icon – . Name your schematic something descriptive. How about “BareBonesArduino.sch” (SCH is the file format for all EAGLE schematics).
As a bonus, after saving, your frame’s title should update accordingly (you may have to move around the screen, or go to View > Redraw).
Step 3: Adding the Power Input
Next we’ll add four different parts all devoted to our voltage supply input. Use the add tool for these parts:
Step 4: Microprocessor and Supporting Circuitry
Next we’ll add the main component of the design – the ATmega328 microprocessor – as well as some components to support it. Here are the parts we’ll add:
Step 5: Adding the Connectors
Three connectors will finish off our design. One 8-pin connector to break out the analog pins, a 6-pin serial programming header, and a 2×3-pin ICSP programming header. Here are the three parts to add for this step:
Wiring Up the Schematic
With all of the parts added to our schematic, it’s time to wire them together. There’s one major caveat here before we start: even though we’re wiring parts on the schematic, we not going to use the WIRE tool – – to connect them together. Instead, we’ll use the NET tool – (left toolbar, or under the Draw menu). The WIRE tool would be better-named as a line-drawing tool, NET does a better job of connecting components.