Soldering

Here’s the schematic again, for reference:

When building two or more poi, you’ll probably find it faster and easier to do each step on all the poi, assembly-line style, rather than building each one start-to-finish.

DO NOT connect the battery to anything until instructed to do so. Soldering on a live circuit can be dangerous.

Power Switch

Cut two 3-inch (75 mm) — or slightly longer — pieces of 26 gauge silicone-insulated stranded wire and strip about 1/8" insulation from one end (to match the pins on the switch). Give the bare ends a twist and “tin” the wires with a tiny bit of molten solder.

Tin two pins of the power switch — the center pin and either of the two outside pins. Then solder the wires to these pins.

It’s vital thoughout this project that the solder flow smoothly between components. Cold solder joints — where the solder is beaded on the surface — do not withstand physical shock.

Fresh solder flux (which is built into the core of the solder) is essential. You’ll have one or two tries to make the connection…any more than that and the solder starts to get sticky and misbehave. When this happens, you can mop up the bad solder with your iron and a solder sucker or copper desoldering wick, then begin again with virgin, flux-rich solder.

Add small bits of heat-shrink tubing over the switch connections and carefully shrink with a lighter or heat gun.

Heat-shrink tubing is not just to prevent electrical shorts, it also provides the solder joints some strain relief against shock and vibration.

Strip a similar amount of insulation from the other end of the wires, twist and tin the ends. Feed these top-to-bottom through the two power switch holes and solder. There’s no specific polarity — either wire can go to either hole.

When the soldering looks good, trim away any excess wire so the bottom of this board is relatively smooth.

Test fit the placement of the switch and LiPoly backpack. You’ll see there’s a little channel for the wires to run through, and a notch that holds the edge of the board.

If there’s a few millimeters of slack, that’s fine. If there’s a whole lot of slack, you’ll need to desolder the wires from the backpack, trim them down a little, and re-solder.

If the wires came up too short, not to worry. Use a hobby knife to cut away the heat-shrink tubing, de-solder the connections from both ends, then cut a new pair of wires a little longer and repeat these steps.

This is what I mean by “fussy.”

Mode Select Button

The steps are very similar to the power switch above…

Cut two pieces of 30 gauge silicone-insulated stranded wire about the same length as the insert. We’ll cut these to an exact length later.

Trim a little insulation from one end of the wires, twist and tin.

Tin the pins of the pushbutton switch and solder the wires here. Again, you’re looking for smooth, reliable connections. 

Heat-shrink the pins once the connections are satisfactory. 

Set this piece aside, we’ll come back to it in a bit.

Why are two different gauges of wire being used?

Heavier-gauge wire has less resistance and can carry more current…but space is so limited here we can’t fit the 26 gauge wire throughout. So the battery and power-hungry LEDs will get 26 gauge, while the microcontroller and signal wires (which don’t require a lot of current) use the slimmer 30 gauge.

Charging Wire

Easy one!

Cut a single piece of 26 gauge wire a little over 2 inches (50 mm) long…or, with the parts laid out atop the insert, you’re aiming to reach from the “5V” pin on the LiPoly backpack to the “USB+” pin on the Trinket.

Strip, twist and tin both ends of the wire and solder those connections, then trim the wires flush.

This wire should be long enough to position the Trinket in this slot, with the USB port protruding just a couple millimeters. As with the power switch wires before, you may need to re-do this to get the length just right.

Battery Distrubution

The weird part!

We’ll now cut a total of eight wires…just a little bit longer than the charging wire…and strip about 1/4" of insulation from one end. Six wires should be 26 gauge, the other two are 30 gauge.

Color-coding the wires for +V and ground isn’t required, but sure does help keep track of things. This makes for two groups each with three 26 gauge wires and one 30 gauge.

Pair up wires side-by-side and twist the ends together. Two of these pairs will be 26 gauge wire, the others two will combine one 26 and one 30 gauge wire.

Now twist pairs together end-to-end. Solder the connections and add just enough heat-shrink tubing to safely cover that area.

You’ll now have two little “bow tie” things with three thicker wires and one thin wire.

Goal now is to route these wires and trim them to exact lengths. I found it helpful to tape everything down for this step.

On the end with two thick wires: route one + and one – wire around either side of the USB connector. These wires will not be trimmed yet.

On the end with the thick-and-thin wires: the thick wires go to the LiPoly backpack — black needs to reach to G, red to BAT, while the thin wires must reach the Trinket’s Gnd and BAT+ pins. Allow a few extra millimeters on each to strip, twist and tin, but do not solder any of these connections just yet.

Well okay, the red wires are pretty straightforward — thick wire to LiPoly backpack BAT, thin wire to Trinket BAT+. Leave the other two thick wires alone for now, straddling the USB connector.

Mode Select Button

…and more power stuff.

install the mode button into the notch at the base of the insert. Like the power switch, there’s a channel for the wires to run through.

Position the other components at their approximate installed distances, then clip the mode button wires to reach the following points (with a few extra millimeters of slack):

  • G on LiPoly backpack.
  • Pin 3 on Trinket.

Strip, twist and tin the ends of these wires.

Now insert and solder TWO wires through the G pin on the LiPoly backpack: the shorter wire from the mode button, and the thicker (26 ga) ground wire.

Try to keep the wires orderly on these last few steps…use tweezers to “comb” the wires apart as needed so they’re not twisted around each other.

Solder the mode button’s longer wire to Trinket pin 3.

The narrower (30 ga) ground wire then solders to the Trinket’s Gnd pin.

Clock and Data Lines

Cut four 30 gauge wires, similar length to all the power wires you previously made. If color-coding, two are for LED data, two for clock.

Strip about 1/4" of insulation from one end of each wire, then pair them up and twist and tin the ends.

Solder one pair to Trinket pin 1 (data) and the other to pin 2 (clock).

Double-check that you’re getting the correct holes, else the poi won’t work. Pin 0 is not used.

That’s all the soldering on the Trinket and backpack! There’s still more to do elsewhere though…

This guide was first published on Jul 13, 2015. It was last updated on Jul 13, 2015. This page (Soldering) was last updated on Apr 22, 2019.