Eagle CAD is a software package used for designing electronic circuit schematics and layouts. The schematic of a circuit is a sketch of how different electronic components are connected together. This schematic is then converted into a layout, which is the actual image of the circuit as it will appear on the Printed Circuit Board (PCB). Usually, rectangular shaped layouts are made. But Eagle CAD has a "MITER" command that can be used to convert a rectangular layout into a circular one.
Start the Eagle CAD software by double-clicking on its icon on the desktop or by going to "All Programs" in the "Start" menu.
Open the layout file by clicking on "File" and selecting "Open". Browse to the layout file and click "OK" to open it. If a layout file has not yet been created, create a new file by going to "File" and clicking on "New". Enter a file name of your choice in the "file name" field and click "OK".
Adjust the size of the board outline according to the size of the PCB. The board outline will appear as a square. Left-click on any side of this outline and drag it to the right or left to adjust the size. Keep the shape as a square so that when attempts are made to convert it into a circle, it does not take an oval shape. The sides of the square should be equal to the diameter of the circle.
Type "MITER 2" in the command bar on top of the layout, then hit "Enter." The mouse icon will convert into a + sign. Left-click a corner of the square. This will make the corner round. If the rounded corner looks too small, try again with "MITER 3" or any higher number. Similarly, decrease the number if the corner looks too large. Repeat this process to round all corners.