The circuit does two primary things:

• reads eight cap touch pins (which each run to ground via >1MΩ resistors)
• sends stereo PWM audio out over the TX and RX pins, via RC (resistor/capacitor) filter circuits

Perma Proto Version

In order to fit the small space inside the Tyrell building model, you'll build the circuit onto a 1/4 size Perma Proto board.

You'll note the flipped TRRS breakout board used to maximize space. The breakout will be fit onto the board via headers in order to provide vertical clearance of the QT Py.

Gather the Components

Prep for soldering by gathering the components. You'll want to snap off two seven-pin lengths of male headers for the QT Py.

TRRS Breakout Headers

Cut of a six-position strip each of the short pin and socket headers. Solder the pin headers under the breakout and the socket to the PermaProto as shown here.

Solder the QT Py Headers

Solder the QT Py to the headers and the Perma Proto as shown. Note how the position leaves room for the mounting hole.

Touch Resistors

Solder the eight >1MΩ resistors from the touch pins to ground. The pins used are A0, A1, A2, A3, SDA, SCL, MISO, MOSI.

Audio Filters

You'll use a pair of resistor-capacitor (RC) filters to smooth out the other-wise harsh PWM audio that will go from pins TX and RX to the TRS jack's left and right channels.

You can also add jumper wires to ground at this point.

Cap Touch Headers

Fit the TRRS breakout into the header and then solder in one set of six and another set of two headers facing up from the board to connect the cap touch cables.

Base Attachment

Use two M2.5 x 6mm screws and nuts to attach the board to the inside of the Tyrell building case base. You can use nylon screws and file them down for a smooth fit, or get a set of low profile "laptop screws" such as these.

Touch Cabling

Cut eight of the jumper wires down to about 4" in length, then strip about 1" of insulation from the tips.

Feed the wires through the holes from the inside of the case to the outside.

Cut a length of copper tape and affix to the side, overlapping the stripped wire as shown. These will act as the cap touch sensors.

Cable Connections

Wire up the cap touch cables to their respective pins as shown.

Plug in the USB-C cable and TRS 3.5mm stereo audio cable -- you can use right-angled cables to help with the fit if necessary. Some straight cables may fit as well, depending on their design.

Route the USB-C and audio cables out of the "back" side of the case with the cable opening.

Close the Case

Snap the base into the main part of the case. You can use M2.5 x 10mm screws to secure it in the corners if needed, but the snap fit should be solid enough to hold it in place.