This project features capacitive touch for each of the ten keys. The keys 1-10 use the PCB as a capacitive touch pad. The inputs, from large copper pads under the buttons, are connected by a PCB via to a 10K ohm resistor and then into an AT42QT1070-S capacitive touch chip. Each AT42 can handle 5 inputs and 5 outputs. So to handle 10, two identical circuits are needed.

The design is directly from the Adafruit AT42QT1070 breakout board and its product guide. It is used in momentary mode, when you touch the pad, an LED comes on.

In the schematic editor, draw two copies of the AT42 circuit with values changed between them appropriately. The battery is specified separately.

Bill of Materials (BOM)

KiCad has built-in PCB footprints for some of these items:

• A Keystone CR2032 battery holder
• 1206 size 470 and 10K ohm surface mount resistors

The LEDs are the same Inolux IN-S124AR LEDs used for the NASA badge. The footprint was tweaked to make the LED hole larger to accommodate reverse mounting. This was not quite sufficient (the board house doesn't like a hole so close to the LED pads) so a bead file is used on each hole to make it even a bit bigger.

Looking at DigiKey, the AT42QT1070-S in a SOIC-14 package (3.9x8.7mm, 1.77mm pitch) was chosen. These were placed above the buttons on the PCB back. The battery holder was placed at the top opposite the Activate button. Care was made to avoid placing components in the bare board area to facilitate light shining through, if desired.

The final bill of materials is below. Prices may change of course and I ordered more of the small parts in case of lose (they are so tiny) and price breaks on the LEDs at 100. Parts were bought to populate 5 boards, the typical minimum number from board houses. But also a good number to have parts for board revisions.

Note: You can buy parts from any supplier, this is not a DigiKey sponsored project.