This project is a fusion of pop culture fandom and electronics engineering, manifesting as a custom-designed Printed Circuit Board (PCB) badge. It is a miniature, functional recreation of the “alphabet wall” used by Joyce Byers to communicate with the Upside Down in Stranger Things.

The PCB is not just a circuit carrier; it is the canvas. It features hand-drawn artwork rendered in black silkscreen on a white soldermask, depicting the A-Z alphabet, the towering Mind Flayer, and the Demogorgon flower. Underneath the art lies an embedded system capable of lighting up individual letters to spell out messages, just like in the show.

• Artistic PCB Design: Custom high-contrast silkscreen art serving as a collectible prop or wearable badge.
• Full Alphabet Control: 26 individually controllable LEDs corresponding to letters A-Z.
• Integrated Sound: A piezo buzzer for eerie sound effects and feedback.
• Portable Power: Runs on a compact battery cell with a simple on/off slide switch.
• Efficient Circuitry: Uses advanced multiplexing techniques to minimize component count.

The heart of the badge is a modern, efficient 8-bit AVR microcontroller. Despite having a limited number of pins, the design controls 26 LEDs individually through a technique called Charlieplexing.

• Microcontroller: ATtiny1614-SS (U1).
• LEDs: 26x Surface Mount LEDs (Mixed colors: Red, Green, Blue, Yellow).
• Audio: Piezo Buzzer (BZ1).
• Power: Battery Cell (BT1) controlled by an SPDT slide switch (SW1).

How Charlieplexing Works: To control 26 LEDs using only a small microcontroller, this design utilizes Charlieplexing. As seen in the schematic, 6 GPIO pins from the ATtiny1614 (PA1 through PA6) are connected to six lines (L1-L6) via 330-ohm current-limiting resistors (R1-R6).

The LEDs (D1-D26) are connected in opposing pairs across these lines. By rapidly switching the state of the microcontroller pins between High (VCC), Low (GND), and High-Impedance (Input), the firmware can target and illuminate any single LED at a time. By cycling through desired LEDs quickly, persistent vision creates the illusion that multiple lights are on simultaneously.