APRS/GPS + Voice Interface: Improved PTT Button Cap

Long ago, Mary picked out a PTT switch with a raised, square post that provided a distinct shape and positive tactile feedback:

PTT Button - bare post
PTT Button – bare post

Time passes, she dinged her thumb in the garden, and asked for a more rounded button. I have some switches with rounded caps, but replacing the existing switch looked a lot like work, sooooo:

PTT Button Cap - Slic3r preview
PTT Button Cap – Slic3r preview

As with all small objects, building them four at a time gives the plastic in each one time to cool before slapping the next layer on top:

PTT Button - on platform
PTT Button – on platform

The hole in the cap is 0.2 mm oversize, which results in a snug press fit on the small ridges barely visible around the post in the first image:

PTT Button - rounded cap
PTT Button – rounded cap

Rather than compute the chord covering the surface, I just resized a sphere to twice the desired dome height (picked as 6 threads, just for convenience) and plunked it atop a cylinder. Remember to expand the sphere diameter by 1/cos(180/sides) to make it match the cylinder and force both to have the same number of sides.

If it falls off, I have three backups.

The OpenSCAD source code as a GitHub Gist:

// PTT Button cap
// Ed Nisley KE4ZNU - June 2016
//- Extrusion parameters - must match reality!
ThreadThick = 0.20;
ThreadWidth = 0.40;
Protrusion = 0.1;
HoleWindage = 0.2;
//------
// Dimensions
Post = [3.8,3.8,3.0];
OD = 0;
HEIGHT = 1;
DOMEHEIGHT = 2;
Button = [12,0+Post[2],6*ThreadThick];
NumSides = 8*4;
//----------------------
//- Build it
difference() {
union() {
translate([0,0,Button[HEIGHT]])
resize([0,0,2*Button[DOMEHEIGHT]])
sphere(d=Button[OD]/cos(180/NumSides),$fn=NumSides);
cylinder(d=Button[OD],h=Button[HEIGHT],$fn=NumSides);
}
translate([0,0,Post[2]/2 - Protrusion])
cube(Post + [HoleWindage,HoleWindage,Protrusion],center=true);
}
view raw PTT Button Cap.scad hosted with ❤ by GitHub

4 thoughts on “APRS/GPS + Voice Interface: Improved PTT Button Cap

  1. This sort of thing is where 3D printing shines. If they all do fall off, it would be simple enough to add a snap ridge on one or more sides.

    1. The layer lines probably serve the same purpose: I could feel it snap along the stud, repeatedly, as I pushed it on.

      In retrospect, I should have made a rectangular button with a domed top…

  2. Ed, these push buttons come in a range of operating pressures. You could chose a type that suits your finger! I found out while trying to find a replacement center button for my mouse. Finally the PTT switch from a defunct FT411 did the job!

    1. You should see all the switches we didn’t use along the way! She started with a flat switch like the one on my bike, tried a few others, then settled on the peg you see here… and now we’re back to a bigger dome. All of them use the same mechanical design to get the sharp click we both depend on to verify that the switch activated: without that, we can’t tell when we’re on the air.

      One of these days I’ll spot a big surplus switch assortment and restock the bin!

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