This article details how to draw schematics in Eagle CAD, aimed at new users. It will show you how to set-up the design, find the components and create a nicely drawn schematic.
The official Eagle tutorial, included with the software is worth reading. It is located in C:\Program Files\Eagle <ver>\doc and is called tutorial_en.pdf. This article provides additional hints and tips on using the software for common tasks and answeres some frequently asked questions from newcomers.
This work is licensed under a Creative Commons Attribution 3.0 Unported License
Step 1 creating a new design
Once you open Eagle CAd you will be presented with a screen like this showing the projects:
On my system, I have created an 'Ians_projects' folder, located outside of the Eagle CAD installation directory, this is to make backing up of the files easier. To create a custom project directory, create a new folder on the PC using Windows explorer, then from within Eagle, select Options-> Directories and you will see the following dialogue box:
You can see my custom project folder on drive F:
Going back to the projects folder, create a new project by selecting the project folder and clicking with the right mouse button, select New Project from the menu.
Then select your new project, double click it and then using the right mouse button, create a new schematic:
This opens up a fresh schematic window
I would now save the schematic, giving it an appropriate name.
Part 2 Adding components to the schematic
The first item to add is a schematic border, to do this, click the Add button, of which there are two, one is a text button the other has a symbol, both are shown here:
I prefer to use the textual 'add' button as I can never remember which symbol is the add button.
You will now be presented with a library browser, in the search windows, type Frame you will be presented with the following results:
I tend to use either the DINA3_L or DINA4_L borders, (note L= landscape, P=Portrait), if you are in the USA or Canada, you may want to use the LETTER_L
Note: even if you only have an A4/Letter printer you can still use the A3 or Frame_C paper sizes, Eagle will scale your drawing to fit the printer page.
Once you click done, you will need to place this symbol. It always place the border so that the origin is in the bottom left of the schematic as shown here:
This helps to centre everything on the page and looks neater, in my opinion.
Finding the components you require in Eagle CAD can be tricky at first, the Add tool allows you to search for components and you can use wildcards so *741* will return every TTL device with 741 but further down the listing you will find the ubiquitous ua741 op-amp you wanted.
A search facility is good but what if you want to browse or do not know how to specify say a 0.5W metal fim resistor or 100uF through hole capacitor? The next section will help
Part 3 finding common components in the library
With the standard installation, Eagle comes with a wide variety of libraries, with more available from Cadsoft and other sources on the internet, which is fine but for commonly used parts, how do you locate them?
Starting with the passive parts first. From a schematic, click the 'Add' button and scroll down to the RCL library and expand it out.
As I am based in Europe, I use the European (EU) symbols for resistors, capacitors and inductors. If you
prefer the US symbols, select them instead.
For any of the libraries, expand the library and you will see a list of components. Use the following table to help find the part you require, note SMT = Surface MounT, PTH = Plated Through Hole.
The values and types listed above are typical based on component data taken from manufacturers data. Always check the sizes for your particular parts to ensure they are the correct size.
Commonly required parts and their location
Finding other components
For the following component types, it is easier to use the search function:
Power converters e.g. 78*05
anything not covered previously
Step 4 drawing the schematic
Hopefully by now you have set-up a new drawing, found the parts you require and placed some parts on the schematic. This section will not teach you how to draw a schematic but it will provide hints on common queries
Adding power pins and logic gates
As an example, your design uses a 74AC04D hex inverter, and you have used 5 gates, how do you load the 6th unused gate, to tie it's input to ground. Use the 'Invoke' button:
Next click the device, IC1 and you will be presented with this menu:
Click on 'Gate' F to load the unused device and click OK, the invoke tool should still be selected so click on IC1 again and select 'Gate' P to load the power pins, then click 'OK'. You have now placed the power pins.
It is easy to forget this step when using TTL logic devices but with any complex part that does not show power
pins, be sure to try the 'Invoke' command.
Adding power nets
Related to the previous section, you will want to add power nets to your design. To do this, use the 'Add' command and navigate to the 'Supply' library, from here you can add a Gnd net and various positive and negative power supply nets.
Check your design
Always check your design, use the design rule check option, either click the DRC icon or use the Tool-> DRC menu item. This will save you some hassle later on.
On my simple example design, with no connections the following errors were flagged up:
Whilst this is to be expected it does highlight the fact that the software checks for unconnected inputs and missing power supplies, very important checks for any design. It will also warn if nets are shorted together.
Updated 27 September 2020