Nuts & Volts - February 2004

Custom Membrane Switches

This makes removing it easy. Also, this particular front panel is aluminum. If you use a plastic front panel, don't center punch too hard or else you'll break the plastic.

Photo 2. The paper work overlay is attached to the front panel with a couple of pieces of double-sided tape.

Photo 3. This shows the results — the PCB is temporarily mounted to the front panel and the work overlay has been removed.

Big Holes for the Switches

Photo 3 shows the results. The PCB is temporarily mounted to the front panel and the work overlay has been removed. Note that the switch holes are about 0.5-inch in diameter. This allows the switch body to extend part way through the front panel. (Be careful with shorts to a metal front panel.) If you use long actuator switches, still use about

0.5-inch diameter holes. This is because the overlay has to flex a little. Holes that are too small won't flex very well.

You may want to experiment.

You will also have to adjust the spacing of the PCB so that the top of the switch actuator is just about level with the top of the front panel. In this case, a single nut provides the proper spacing.

trimmed-to-size overlay. If you have air bubbles, carefully pierce the paper to let the air out. Don't pierce the tape or else it will eventually tear there.

Carefully place the overlay on the front cover. This is the hardest part. You have to make sure that the alignment is perfect before you press down. If you try to move the overlay after it's stuck to the tape, it will almost certainly tear. I shine a bright light behind the front panel so that the holes shine through the overlay. This makes alignment easier. Once you are sure the alignment is correct, press the overlay down from the middle to the edges. There is no easy way to remove air bubbles.

Trim away the excess double-sided tape. This should look like Photo 5.

Attaching the Overlay

Final Assembly

Remove the PCB and put double-sided tape on the front panel. Use strips side by side, without any overlap. Be sure that this tape is wider and taller than the overlay — the excess will be trimmed off.

Again, extending the tape beyond the front panel makes trim removal easier. Remove tape from all openings in the front panel. An Xacto knife works well for this. See Photo 4.

Use the package sealing tape to cover the overlay — and be careful — this step shows any and all mistakes. (It's often worthwhile to have several spare paper overlays.) If the overlay is wider than the tape, you can either put the next strip side- by-side or overlap slightly (about 1/8-inch). If you overlap, try to place the seam away from switch openings.

Note, I find that putting tape on the overlay and then trim-ming/cutting the overlay to size from the paper easier than trying to put tape on an already

FEBRUARY 2004

Carefully cut through the overlay for the PCB mounting holes. Attach the PCB with the proper spacers. The membrane switch should now work (see Photo 6). You may want to experiment with the spacing to provide the switch feel you like.

Variations and Notes

This particular version had only the switches on the

PCB. If you want to mount parts on the PCB, there are two basic ways to do that.

First, use tall actuator switches. This allows parts to be placed on the same side as the switches. This requires longer spacers and obviously limits the height of the parts. The second way is to put the parts on the "back" side of the PCB. However, in practice, it would be the switches that are mounted on the back of the PCB while the parts are on the front.