But first…a few wires need to be cut to about six inches long. You don’t need a ruler for this…the ribbon cable is just the right length. Unplug it from the Pi and PiTFT and use it for reference.
This isn’t rocket surgery, don’t worry if wires aren’t precisely the right length. Six-ish inches is fine!
24 gauge stranded wire is ideal. A little thicker or thinner is okay, as is solid-core wire…stranded is simply more flexible.
Color-coding the wires likewise isn’t essential; one color will suffice if that’s what you have.
Optional: you can keep these wires together with a bit of heat-shrink tube if you like.
Strip about 1" of the outer jacket only to reveal the three wires inside: two are insulated, the third is bare copper.
Some headphone cables have red and black wires rather than the red and white shown here. This is OK, it all works the same. Red is the right channel, black or white is the left channel, copper is ground.
Slide a small piece of heat-shrink tube a few inches down the cable (around the whole thing, not just the copper wire).
Slide a second piece of heat-shrink tube over just the copper wire and heat it up. This covers most of the wire, but there’s still a tiny gap.
Slide the first (un-shrunk) piece back up so it covers the gap, apply heat.
It’s easiest to do the JST sockets first, one at a time. You can temporarily hold them with a little tape, or place each one “legs up” on the table and lower the board in place, then solder.
Notice how the two rows sit “back to back.” This makes it a little easier to unplug the connectors later.
The 26-pin Raspberry Pi header then mounts on the underside of the board, with the pins soldered on top. Make sure the notch on this header matches the outline on the board!
Install a 5-pin header from below.
Make sure all your solder connections are smooth and clean, like tiny Hershey’s Kisses®. There should be no solder balls or bridges, no gaps between pins and their corresponding pads.
Switch off your iron, all the soldering’s done now!