There’s not a huge amount of soldering involved, but the tight quarters make this project a challenge.
Additionally, since the die will be dropped and rolled around a lot, the solder connections need to be really solid. Cold solder joints — where solder beads up on surfaces and hasn’t flowed smoothly between components — don’t handle physical stresses and will soon fail. The Adafruit Guide to Excellent Soldering shows what good (and bad) solder joints look like and how to avoid common pitfalls.
Here’s the wiring diagram again for reference. This is laid out to make the connections clear, not as an indication of wire lengths:
When installed in the die, some of the boards are stacked: the amplifier sits underneath the sound board, accelerometer under the Pro Trinket.
We can use fairly short wires between stacked boards, longer wires for any connections across…everything will be trimmed to an exact length later. Some wires will be soldered top-to-bottom, others bottom-to-top.
Cut two wires about 3 inches long. Strip and tin one end and solder to the power switch — use the center pin and either of the two outer pins, doesn’t matter which.
Heat-shrink tubing is optional here, use it if you’ve got it. Though best known for preventing electrical shorts, heat-shrink is also a strain relief, so solder connections are less likely to break with repeated dropping.
Solder a short wire between the UG and nearby GND pin on the Sound Board.
This configures it to run in UART mode (operated from a microcontroller) rather than the trigger pins.
Next we’ll add a few wires to the tiny amplifier board…but the Sound Board is borrowed as a measuring stick of sorts. One board will be stacked atop the other, so we know any connections between the two won’t exceed this length.
Cut four wires just a little longer than the Sound Board. Two are for power, two for audio. Then cut two wires about 4 inches long, for the speaker.
Strip a small bit of insulation from just one end and tin each wire to prevent fraying.
The four short wires go to Vin and GND (for power) and A+ and A– (audio input). The two long wires go to the 4–8Ω audio output (do not install the screw terminals, solder the wires directly).
Cut one more wire in-between these lengths. Strip, tin and solder it to the SD pin.
After the solder has cooled, trim and protruding wires from the underside of the board, and make sure any clippings end up in the trash, not in the d20. Do the same with other boards as you work through the project.
Six wires need to run between the Pro Trinket and Sound Board. Two are for power, four for various signals. Using either board as a measuring stick, cut these wires to about 2X the board’s length. Strip a little insulation from one end and tin each wire.
The two power wires connection to the + and – pads on the underside of the Sound Board. Tin these pads first with a little solder, then hold the previously-tinned wire in place and re-melt the solder to join the two. The solder joints need to be smooth and shiny, not beaded up on the surface.
The other four wires connect to TX, RX, Act and Rst.
Cut three wires about 1 inch long. Strip, tin and solder to the BAT, G and 5V pins on the LiPoly Backpack board.
The accelerometer and Pro Trinket boards will also be stacked…so again, we can use the longer board as a measuring stick.
Cut five wires about 1.5X the length of the Pro Trinket. These connect to VIN, GND, I2, SCL and SDA. But notice we’re feeding these wires through from the back…that’s because the accelerometer gets installed “face down” later.
This next sequence requires patience and dexterity. If you clip a wire too short, don’t stress over it, they’re easily replaced at this stage.
Temporarily install the accelerometer (face down) and amplifier (face up)…a single screw should be sufficient for now.
Our goal is to find the ideal lengths for each wire. To do this, we’ll hold each of the top two boards in place and “tweezer comb” each wire from the lower board to its corresponding point on the upper board (using the wiring diagram for reference), then cut. Allow several extra millimeters slack on each wire, for moving around and stripping later.
Do the amp-to-sound-board wires first, then the accelerometer-to-Pro-Trinket wires, and finally the six “across” wires from the Sound Board to Pro Trinket.
The speaker wires should just be routed out the back for now.
Now that every wire’s trimmed to an exact length, strip a little bit of insulation and tin the end of each one. All of them! Do this for the LiPoly backpack board and power switch wires as well.
Tinning the wires is important. A single stray wire strand can cause shorts or wreak other havoc.
Using a piece of tape or some glue, cover up the solder pads on the back of the LiPoly Backpack to prevent it from shorting against other parts later.
Another “patience and dexterity” sequence, making the connections between boards. Use the wiring diagram for reference.
Let’s do all the bottom-to-top wires first…connections from the accelerometer to Pro Trinket and from the amplifier to the Sound Board…these wires contact the upper board from below and are soldered on the top.
Then do the two power wires…the + and – pads on the bottom of the Sound Board are linked to the corresponding pads on the Pro Trinket.
Finally, we’ll do all the top-to-bottom wires…the main board connections with the wires on top and soldering underneath. Add the LiPoly Backpack wires to the Pro Trinket as well, and the power switch to the Backpack.
Last step is to solder the wires from the amplifier output to the speaker. Notice how they’re turned around now, so the wires don’t extend off the side. Space is at a premium!
There should be no loose wires at this point. Every connection should go from one place to another. Double-check all the connections against the wiring diagram before moving forward!
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