| FreePCB User Guide | Version 1.2

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7. Tutorial (continued)

7.5 Adding Mounting Holes

Now we will add mounting holes at the corners of the PCB. You might want to review Section 5.12: Mounting Holes before starting.

- Mounting holes are actually a special type of part, consisting of a single through-hole pin. They are added to a project like any other part. They can be included in the netlist file, or they can be added later. Since our netlist file did not include the mounting holes, we will add them using the Ad d > Pa rt menu.
- Set the placement grid to a small number such as 25 mils.
- Select Part from the Add menu. The following dialog should pop up

- Enter "H1" in the Reference field of the dialog. This will be the reference designator for the first mounting hole.
- Expand the C:\FreePCB\lib\th_mounting_hole.fpl library file by clicking on the "+" next to it. Then click on "HOLE_125_SQUARE_250". This is the footprint for a mounting hole 125 mils in diameter, with a square pad 250 mils in diameter. It is about the right size for a #4 machine screw. Now the dialog should look like:

- Click OK to close the dialog and begin dragging the mounting hole. Move it to X = 150, Y = 150 as shown below.

- Click the left mouse button to place the hole. Now the layout should look like

- In similar fashion, add 3 more mounting holes at the other corners of the PCB, using reference designators H2, H3 and H4, as shown below. Note that when you use the Add > Part dialog to add these holes, it will come up initialized with the last footprint that you added, with the reference designator incremented by one, so you only have to click OK or press "return" to add the next part.

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- Now we will connect H4 to the GND net, so that it can be used to ground the PCB to its enclosure. To do this, we must select the pin H4.1, instead of the part H4, since connections are always made to pins .Notice that in the screen shot above, the selection rectangle around H4 does not have an "X" through it, indicating that the part is selected and not the pin. The status bar also shows that part H4 has been selected.
- To select the pin for H4, click anywhere on the pad. Now the selection rectangle should contain an "X", and the status bar should indicate that pin H4.1 has been selected, as shown below. If you wanted to reselect the part (to move it, for example) you would click again on the pad.

- With the pin selected, press F1 ("Set Net"), which pops up the following dialog. Use the drop-down menu to select the GND net, as shown.

- Click OK to assign H4.1 to the GND net. A ratline to the pin should appear.

- Now we will connect H3.1 to GND, by drawing a ratline from H4.1 to H3.1. With the pin H4.1 still selected, press F4 ("connect Pin"). Now you will be dragging a ratline from H4.1. Place the end of the ratline over H3 and left-click to connect H3.1 to H4.1, as shown below.

- In similar fashion, connect H4 to H1 and H2.

- Now press F8 ("Recalc ratlines") to redraw the ratlines to minimize their total length.

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