There are two kinds of wires in Autodesk EAGLE, the standard Wire, and the Net. But which do you use when creating connections between your symbols? Here’s how it works:
You don’t want to use the Wire icon when adding nets to your schematic. The only reason to use the Wire option is for adding detailed line drawings to your schematic.
You do want to use the Net icon to wire up your schematic symbols. This will always be your go-to action when you need to connect your symbols together.
This can be a tad confusing at first, but use the icon symbols as a visual guide. The Net icon is a green wire representing connectivity, which is exactly its purpose. Whereas the Wire icon has a line and a pencil. Use this feature, not the pencil for creating sketches.
Next, you’ll need to understand the difference between junctions and overlaps. Here’s an example of a junction:
You can always identify a junction by the large circle that connects two intersecting nets. This means that these nets are sharing an electrical connection. This is a universal symbol, so be on the lookout whenever you see it in any schematic down the road.
Now, when nets aren’t meant to share an electrical connection, then they will overlap. In Autodesk EAGLE, you’ll know when two nets are overlapping when there is no junction point between their intersection, like this:
What’s so important about all of this? How you place your nets in your schematic will determine how your parts are electrically connected and will affect your PCB layout as well. If you don’t get this part right now, then your circuit won’t work as intended, and that’s no fun.
That’s it for the getting starting details. Let’s begin wiring up your schematic with nets!
Before you go about adding any nets, let’s first add a grid to your schematic. This will make it a lot easier to see how all of our symbols are aligned and will let you easily see what course your nets will align with when placed. Follow these steps to turn on your grid
Turning on your grid will make a lot more sense once you start connecting nets, and it works much better than the blank white canvas with which that you started.
Now that you have some structure in place with a grid let’s move on to connecting your symbols with nets!
Connecting your symbols with nets is simple. Follow these steps to get started:
In our example shown below, we started with a simple net connection between the bottom of our R3 resistor and the top of our R4 resistor. Pretty easy? Now let’s find out how to add some junctions.
As we mentioned above, adding junctions to your schematic allows intersecting nets to share an electrical connection. To add a junction, you can do it in one of two ways:
We need to add a net that connects between Pin 3 on our 555 timer and our R3 and R4 resistors. This will require a junction. You can follow these steps in our example to add one:
Creating a junction while adding a net is easy, but what happens if you have two intersecting nets that don’t already have a junction marker? You can add one manually:
You just added both regular nets and junctions, what happens if you make a mistake? Here is how to delete a net:
Now you have all the basic building blocks you need to wire up your symbols. The completed schematic is below. Give it a try!
Note – You’ll notice that Pin 5 is not connected on this schematic. That’s done for a very good reason, which we’ll be exploring in Part 3 of this Schematic Basics series.
You might have noticed that when you select the Net icon, quite a lot of new options appear at the top of your interface. These options allow you to set a different bend radius on the net with which you’re working. By default, all of your net connections will use the Wire bend style 0, which is a 90-degree bend, which is fine for most schematics.
However, you may want a 45-degree bend angle for your net. To do this, select the Wire bend style 1 and then add your net as described in Step 2 above. You’ll notice that the net will now automatically bend at your desired angle as shown below:
There are a few other options in this menu, allowing you to add things like a custom radius, or even changing how the net line appears as either solid (continuous), dashed or dotted. Feel free to play around with these options to see how they make a difference. When you’re ready, let’s move on to the final step in today’s schematic journey, adding values to your symbols.
Adding values to specific parts like your resistors, capacitors, etc. will make it easy your reference in the future. Here’s how to add values to your symbols:
That’s all there is to it! As you can see in the image below, our R1 resistor now has a 1k value listed below its name. If you’ve been following along with our example circuit, then go ahead and add the remaining values for the three resistors and capacitor as well.
Quick side note – If you also want to change the name of one of your symbols, it’s almost the same process as changing the value. The only difference being that you’ll select the Name icon instead of the Value icon.
Let’s say you need to delete or change a symbol value that you just added. You might be thinking to use the Delete action, but this will end up removing the entire symbol and value! This is definitely not what we want, so here’s the better way to do it:
You did it! Your schematic should now be fully wired with a set of values added for all of the parts that needed it. Here’s how your schematic should look completed:
This brings us to the end of Schematic Basics Part 2, so let’s take a moment to recap the major concepts you learned today: