Install Headers on Feather
Let's start this build by installing headers onto the pins of the Adafruit Feather. The Feather should have shipped with two sets of headers. They come with extra pins, so you'll need to trim so they fit into the pins. Once installed, you can secure it to a breadboard. This will make the soldering the headers much easier.
Solder Headers on Adafruit Feather
Once the header pins are in place, solder each pin to create solid connections.
Remove Header Joiners from Headers
In order to create the proper clearances for mounting to the enclosure, you'll need to remove the plastic "joiners" from the two headers. I used a pair of flush diagonal cutters to lift the plastic away from the pins.
Install Feather to PCB
Once the plastic joiners are removed from the headers, you should be able to install the Adafruit Feather into the Cherry MX PCB. The microUSB port should be facing the edge of the PCB. The two PCB's should be flush with each other.
Secure PCB to Vise
Now it's time to solder the pins from the Adafruit Feather to the Cherry MX PCB. I recommend using a Panavise Jr. to secure the PCB while you solder.
Solder Feather to PCB
With the Cherry MX PCB secured, you can solder the pins on the four corners to secure the Adafruit Feather in place, then solder the pins from the switches.
Trim Pins on Feather
You'll need to trim the excess pins from the Adafruit Feather. I recommend using flush diagonal cutters. Pro Tip: Place the tip of your finger over the pin before cutting – this will prevent the pin from becoming a projectile.
Install Cherry MX Switch to PCB
With the Adafruit Feather soldered to the Cherry MX PCB, it's time to install the Cherry MX switches. I suggest installing just one. I recommend using mounting tack to temporarily hold it in place while you solder.
Solder Switches to PCB
Once a single switch is in place, solder the pins to the Cherry MX PCB. Then, repeat this process for the other switches. DO NOT install / solder the switch that is closest to the JST port on the Adafruit Feather. If we do, it will become difficult to connect the lipo battery.
Before we can solder the last Cherry MX switch, we'll need to connect the male JST connector from the battery to the female JST connector on the Adafruit Feather – If we connect it now, the circuit will automatically power on. So, before connecting the battery, we'll need to wire in a Slide Switch to power the circuit off.
Prep Slide Switch
Set the Cherry MX PCB aside and grab the slide switch and two pieces of wire. They can be about 100mm (4inches) in length.
Strip and Tin Wires
Use wire strippers to remove about 10mm of insulation from the tips of each wire. Then, secure them to a pair of helping third hands. Once secured, you can tin the exposed wires by applying a bit of solder – This will make it easier to connect the wires to the lead of the slide switch. Tinning wires also prevent stranded wires from fraying.
Solder Wires to Slide Switch
We'll only need two of the three leads from the slide switch, so we can remove one (either the far left or right, but not the middle!) Secure the slide switch to the helping third hands and tin the two remaining leads. Then, solder the wires to the leads on the slide switch.
Connect Slide Switch to Feather
Now we can connect the wires from the slide switch to the Adafruit Feather. Secure the PCB to the panavise jr. Then, solder one wire form the switch to the EN labeled pin (enable) and the other to the GND (ground) pin on the Adafruit Feather. Doesn't matter which wire goes where, as long as they have a solid connection.
OK, now that we have our slide switch wired to the Adafruit Feather, we can connect the battery. Flipping the switch switch will allow you to power the circuit on and off.
Install Last Switch to PCB
Now it's safe to install the last switch to the PCB. Again, use mounting tack to keep the switch in place while you solder the final connections.