At Apex, we use the CadSoft Eagle software for designing our schematics and PCBs – it can be downloaded for free from http://www.cadsoftusa.com/downloads/?language=en
Before starting a schematic design, we fully recommend you follow the SparkFun Schematic Tutorial. It will teach you the basics of using Eagle, laying out a schematic, etc.
The Apex Eagle library is a must-have if you are designing a schematic for a piece of Apex electronics, and any new parts should be added to the library and pushed to the GitHub repo.
Libraries are placed in the C:\Program Files\EAGLE-version\lbr\ directory (in Windows). They then need to be activated in the main eagle window: in the list of libraries in the window, you’ll see all the libraries have green dots next to them showing that they are on. The one you just added won’t, click on the dot and it will turn green and be activated.
If you cannot find a part, then you will need to create your own – follow the SparkFun “New Part” tutorial at http://www.sparkfun.com/tutorials/110
- Schematics should be started with the “Apex A3 Frame” and filled out correctly using the text tool.
- Please include the Apex logo part: it will be needed on the PCB. (The smaller version is probably better)
- Always try and use parts present in the Apex library, then fallback to the SparkFun library and then to the default libraries.
- Use 0805 sized resistors and capacitors from the Apex library – these are what we have available.
- A 100nF capacitor should always be placed between the Vcc and GND pins of ICs used. This is a decoupling capacitor to reduce noise and protect the IC. When it comes to designing the PCB, this will need to be placed as close as physically possible to the corresponding IC.
When you are ready to begin, click the convert to PCB button in Eagle to begin work on the PCB. Make sure to have both the schematic and PCB files open at all times to avoid any problems with Eagle.
- Begin with setting the board size, generally we try and use a 5cm × 5cm PCB if Surface Mounting.
- Always begin with laying out the parts in the most optimal way.
- Headers, connectors and switches are best put around the edges of the board.
- Try to ensure ratsnest lines aren’t too much of a mess – if the ratsnest looks tidy, it will be much easier to route.
- When you come to routing, never use right angles – always use an angled corner.
- Try and route as many of the traces as possible on the top of the board first.
- Place a ground plane on the back and route connections to ground by using a via to the bottom copper. Try not to put digital/logic signals through vias or on the back.
- Ensure decoupling capacitors are as close as physically possible to their corresponding IC.