Display Connection
First, solder in the short Feather headers as shown in the picture here. Be sure to use the short headers or the case will not fit!
Wire the display as shown in the Fritzing diagram and the photos here to the FeatherWing Doubler.
Note: the photos can be confusing, always double check against the circuit diagram!
There are many ways to do this -- I soldered on right angled headers and Dupont connector silicone jumper wires.
Amp Prep
Solder on header pins to the amp board so you can mount it to the Doubler.
I chose to solder a small socket header to connect the amp breakout to the headphone jack using jumper cables later.
Amp Connections
Solder the amp breakout to the long free row of the doubler as shown.
Then, use short wires (such as wire scavenged from an old CAT5 cable or solid core hook up wire with the insulation scraped off at the ends) to connect the legs to their respective pins on the Feather via the Doubler connections.
Amp Gain Resistor
Solder a 100KΩ resistor from the Gain pin to the Vin pin. This sets the amplifier gain to 3dB, which works well for the headphone output.
Headphone Out
To keep the project simple we're using a single mono amplifier. Since most headphones have a stereo TRS 3.5mm plug, you'll run the audio signal to both the tip and ring connectors.
Run a single wire to the ground connector.
I used Dupont connector cables for this and dressed them with heat shrink tubing.
On/Off Switch
Solder a wire from the Doubler/Feather Enable pin to one side of a SPDT switch, and another wire from GND to the center position of the switch.
NeoKey 1x4 and QT Rotary Encoder
Use STEMMA QT cables to connect the Feather to the NeoKeys and rotary encoder breakout.
Plug in the battery as well -- since the amp Vin is connected to the Feather's Bat output you'll need the battery connected even when plugged into USB for coding.
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