Before doing any soldering or other work, do this: using a small dab of E6000 glue or 5 minute epoxy, reinforce the wires coming off the LiPoly battery.

Peel the tape up a little and get the glue underneath, where the wires connect to the board. Don’t let the metal E6000 tube contact the terminals! Set aside to dry completely.

Use a hobby knife or a file to scratch away the trace between these two solder pads on the LiPoly backpack. This lets us add a switch later.

If your power switch has these long legs (not all do), trim them down to about half their size.

Desolder the wires from the speaker. We’ll be adding our own later.

The various boards used in this project have different mounting hole sizes and component clearances. To make our hardware all fit and to play nice with the 3D-printed parts, we have to take some slightly uncouth actions…

First, mounting holes on each board need to be reamed.

The optimal tool for this is a 4-40 thread tap. Few folks will have this tool around though. As an inexpensive proxy, you can use either a 4-40 self-tapping machine screw, or even a #4 wood screw.

The key to successful tapping is to not grind the tool through in a single pass. Instead, turn the tap or screw 1/2 to 1 turn forward, then 1/4 turn back. Then repeat…another 1/2 to 1 turn forward, 1/4 back…keep going until the mounting hole is threaded all the way through.

DO NOT tap the center mounting hole of the Pro Trinket.

On the Pro Trinket, only the two corner holes should be tapped. The center mounting hole is very close to some vital signal traces!

Then test-feed a 4-40 machine screw through each hole.

If you used a 4-40 tap or self-tapping screw, the threads should match. If you used a #4 wood screw instead, the threads will be a little different, but you can still coerce the machine screw all the way through…the fiberglass of the circuit board is slightly pliable.

The Pro Trinket has the smallest mounting holes of the bunch, and these will probably get stretched out, maybe even slightly broken. That’s okay, we can reinforce those points with a bit of glue later when installing.

After reaming these holes, clean away any copper rivulets that may be hanging on. You don’t want these dropping off later and causing electrical shorts.

Mounting circuit boards using countersunk screws (rather than round head) is not usually done, but affords us just a little extra clearance around neabrby components, making electrical shorts less likely.

The Plan

Here’s a wiring diagram you can refer to later…maybe even print this out. The physical arrangement of parts won’t look exactly like this…it’s mostly to make all the connections between parts clear:

Red and black lines are power and ground, respectively. Other colors represent various signals…you don’t actually need to color-code everything like this, but it helps prevent mistakes if you do have some different colors of wire available.

26-gauge silicone-coated stranded wire is the bee's knees for this stuff. Super flexy, and the insulation doesn’t shrink when soldered.

This guide was first published on Aug 07, 2015. It was last updated on Aug 07, 2015. This page (Prep Work) was last updated on Jan 19, 2020.