Devlog #2: Schematic Finalization, Feature Upgrades & PCB Layout Setup

Following up on Devlog #1, I’ve made huge strides in expanding the macropad’s hardware capabilities, solving schematic design checks, and transitioning into physical PCB layout in KiCad!

🚀 Key Feature Additions & Hardware Expansion

Since Devlog #1, I updated the schematic from a basic key matrix to a feature-rich, high-performance design:

I2C Port Expander Integration: Replaced the simple diode-isolated matrix with an MCP23017 I2C expander IC. This offloads all 9 mechanical switch inputs to a dedicated chip, freeing up critical GPIO pins on the XIAO ESP32-S3 for fast SPI graphics.
EC11 Rotary Encoder Added: Integrated an EC11 encoder with push button for smooth scrolling, volume control, and mode toggling.
1.8” SPI TFT Display & SD Card Slot: Added headers for a 128x160 color TFT display running over hardware SPI (SPI_SCK, SPI_MOSI, TFT_CS, TFT_DC, TFT_RES) along with an SD card reader interface (SD_CS) for loading images and macros.
Per-Key RGB Lighting: Added 9x WS2812B addressable RGB LEDs (C1–C9) daisy-chained on a single GPIO line for per-key lighting and animations.

📝 Activities Completed Today

Power Filter & Decoupling Circuitry:
- Added 100nF ceramic decoupling capacitors across VDD and GND for all 9 WS2812B RGB LEDs (C1–C9) and the MCP23017 IC (C10) to eliminate power noise.
- Selected and added a bulk 22µF 16V MLCC ceramic capacitor (0805 footprint) (C11) directly across the main 5V line near the Seeed Studio XIAO ESP32-S3 module to handle current spikes when LEDs flash full brightness white.
Board Stackup & Design Rules:
- Configured PCB properties to a cost-effective 2-layer stackup (1.6mm thickness, FR4).
- Resolved mechanical mounting pad (MP) warnings on the EC11 rotary encoder footprint.
- Set up custom Net Classes:
  - Power Class (5V, 3V3): 0.60mm track width, 0.25mm clearance, 0.8mm/0.4mm via sizing.
  - Default Signal Class: 0.25mm track width, 0.20mm clearance.
Layout Alignment & Ground Plane:
- Configured a custom 19.05mm (750 mil) grid in PCB Editor preferences for exact mechanical key switch alignment (Alt+1 shortcut).
- Created and rendered a full GND Copper Zone (B.Cu) across the bottom layer with thermal reliefs for clean ground grounding and easy hand-soldering.

📋 Checklist Status

Add Rotary Encoder, TFT Display, and RGB LED components to schematic
Finalize footprint assignments for all components
Save footprint assignments and launch the PCB Layout Editor
Define PCB edge outline and arrange all mechanical component footprints
Complete trace routing for signal, SPI bus, and RGB power chains