Kick-off your PCB Project with EAGLE – Part 1: Creating a Schematic

Posted by Maja Filaković Friday, Oct 13, 2017
Eagle logo (Source: https://www.autodesk.com/blogs)

This is the tutorial for all of you, who at some point in your life had an idea about making your own electronic device, but didn’t know where to start and how. Fear no more, because I’m about to show you how to make your Printed Circuit Board (PCB) from scratch, using Autodesk’s CAD tool EAGLE.

PCB design, in general, is a two-step process. When you have an idea, the first thing you’ll need to do is to design a schematic of your device. After you’re done with creating a schematic, the second step is to design a PCB based on it.

This is Part 1 of the tutorial, and I’ll explain to you how to make a schematic, based on the real example of my Music Pen project. I will not go through the installation of the EAGLE, so going further I presume that you’ve successfully installed it on your PC. 
Let’s get started!

Create a Project

In the control panel screen, under the “Projects” tree, right click on the “eagle” folder and select “New Project”.

The new project will be created, so you should give it a descriptive name. In this example, we’ll call it “Music Pen”.

Project folders are like any system folders, except they contain a file name “eagle.epf”, which links your schematic and PCB board design together. It also contains both of those files.

Create a Schematic

To add a schematic to our newly created project folder, right-click on the folder and select “New” and click on “Schematic”.

After this, a blank window opens up, which is where you’ll draw your schematic design.

Adding Components

OK, so the first step is to add all of your components to the schematic sheet and then those parts need to be wired together. If you have a complicated design, sometimes it’s better to add a few parts, wire a few parts, then add some more parts and then wire those together. But, since our project is not that complicated, we’ll add all the parts at once.

Click on the “Edit” menu and select “Add” tool.

This tool is used to place every single component on the schematic. It opens up the library navigator, where you can expand specific library and view the components it holds. On the right side of the window, you should see both schematic symbol and its PCB footprint.

But, before adding our first component, it is a good practice to keep your schematic clean and organised. In the “Search” part, type in “*frame*” and press “Enter” key. This will search through a library and return all matches which correspond to our query. Among these, we are interested in the one called “LETTER_L”, under “frames”. To add it, select it and click “OK”.

The “Add” window will disappear, and the component will follow your mouse cursor. To place the part, left-click where you want it. To exit the place-component mode, hit the escape key.

Now, let’s now add our first component, the NE555 Timer. Follow the same procedure as for the frame, and add the timer to the schematic, inside the frame borders.  ​

Follow the same procedure and place the rest of the components on the sheet, as shown in the figure below. Here are all of the components needed for our project. Note that this is only one example of placing the components on the sheet. The standard practice is to distribute the components so that the wires overlap as less as possible. One important thing, don’t forget to save your work once in a while!

In the following table is the list of components and libraries used in the schematic design, together with their labels on the schematic.

Wiring it all together

Now it’s time to connect our components. We will use “Net” tool to accomplish this. Click on the “Draw” menu and select “Net”.

When you hover over the pin of the component, the circle will appear indicating that this is the connection point. Left-click on it once to start a wire. A green line will be following your mouse cursor around until you terminate the net by left-clicking on either another pin or a net.

Go ahead now, and connect the rest of the components. The final design should look like this:

Notice that some wires that are overlapping have the little dot on the junction, while some don’t. The dot on the junction of the wires indicates that those wires are all connected. When the dot is not present, the wires on that junction are not connected and are just skipping each other.

You can see that I’ve added some values to the capacitors, resistors and headers, and reordered the labels a little bit. To add values to components, right-click on the component and select “Properties”. In the properties window, under “Value” you can enter some value which will be shown alongside the component.

To reorder the labels, first right-click on the component and select “Smash”. This will un-group the labels from the component, which is indicated by the tiny cross near each of the labels. To move it, simply right-click the label and select “Move”. The label will follow the mouse cursor, and you are free to place it wherever you find it fit.

The final part is to test schematics for electrical errors. This is called Electrical Rule Check (ERC) and it is quite useful for detecting if some pins aren’t connected but should be. It is a good practice to run this check when you are done with connecting all components because it will detect any errors with nets, even if you don’t notice it yourself. To run the ERC check in the menu click on “Tools” and select “ERC”.

The tool scans the schematic and if the errors and warnings exist, the window listing them will pop-up, shown in the figure below. If the window doesn’t show up, you got nothing to worry about.

In our case, a window showed up. We can see there is one error and one warning. The error which states that we have unconnected pin is actually not an error, because we don’t have to connect this pin anywhere for the design to work. To get rid of the false error, select it and click on “Approve”. This will tell the ERC tool that this is not an error in our case. The warning states that the power supply pin label on IC1 component differs from our label of the VCC. This is also not an issue for us, so do the same as for the error.

And there you have it; your schematic design is finished. Stay tuned for part 2 of the tutorial, where I’ll be guiding you through the PCB design of the Music Pen.

comments powered by Disqus

news / events / blogs