• Status: Draft
• Device: Standalone USB-C macropad based on ATmega32U4 in TQFP-44 package.
• Goal: Production-intent schematic and PCB setup for a keyboard-style controller with 11 mechanical keys and one EC11 rotary encoder.

• USB HID macropad for desktop use.
• Designed for mass production rather than hand-wired prototyping.
• Mechanical fit will be finalized from a case STEP model supplied later.

• Connect to a host over USB-C as a USB device.
• Scan 12 key inputs: 11 Cherry-MX hotswap switches plus the EC11 integrated push button.
• Read EC11 encoder A/B quadrature channels.
• Support reset and boot/HWB configuration for ATmega32U4 firmware workflows.

• ATmega32U4 SMD TQFP-44 MCU.
• 16 MHz external crystal with two 22 pF load capacitors.
• RESET pull-up and reset pushbutton.
• HWB 10 kΩ pull-down.
• One 100 nF decoupling capacitor per VCC/AVCC pin plus 4.7 µF bulk capacitance.
• USB-C 16-pin SMD connector, D+/D- 22 Ω series resistors, USB ESD protection, and 500 mA resettable PTC on VBUS.
• 11 Cherry-MX hotswap switch footprints and EC11 encoder footprint.
• 1N4148W SOD-123 diode for each key path including encoder pushbutton.

Diagram

• ATmega32U4 TQFP-44 with external 16 MHz crystal.
• Load capacitors specified as 22 pF per user requirement.

• 12 individual key inputs routed to Arduino-compatible ATmega32U4 pins: D2, D3, D4, D5, D6, D7, D8, D9, D10, D14/MISO, D15/SCK, D16/MOSI.
• Each key path includes a 1N4148W SOD-123 diode.

• EC11 rotary encoder with integrated pushbutton.
• Encoder A/B channels connect to Arduino D18/A4 and D19/A5.
• Pushbutton is included in the 12-key diode-protected input set.

• USB-C device/sink connector with CC pull-downs required for USB-C VBUS attach.
• D+/D- protected with USBLC6-2SC6-class ESD protection near connector.
• 22 Ω series resistors between protected USB data lines and ATmega32U4 USB pins.
• 500 mA PTC fuse in series with VBUS.

• Powered from USB VBUS only.
• No battery or charging subsystem specified.
• Estimated system current is well below 500 mA for MCU plus passive keyboard inputs; LED lighting is not specified and not included.

Diagram

• PTC requested: 500 mA resettable fuse.
• Actual load expected: ATmega32U4 plus switches/encoder and leakage currents; no high-current loads specified.

• SMD production-oriented design.
• MCU package: TQFP-44.
• Key diodes: 1N4148W SOD-123.
• USB connector: 16-pin SMD Type-C.
• Switches: Cherry-MX hotswap footprints.

• Maintain Arduino pin mapping exactly as specified.
• RESET and HWB circuits included for bootloader/DFU workflows.
• USB data path supports ATmega32U4 native USB.

• Board outline and switch/encoder positions will be defined after user provides the case STEP model.
• Routing must not be performed until mechanical alignment is complete and locked.

• Use 5 V USB VBUS as VCC for ATmega32U4 unless later requirements require 3.3 V operation.
• Add USB-C CC pull-down resistors even though not explicitly listed, because a USB-C sink needs them for normal host power attach.
• Defer final board outline, mechanical placement, and routing until STEP model is available.
• Initial PCB setup uses a temporary 160 mm × 100 mm 2-layer staging board with top/bottom GND pours. Final outline and exact component coordinates remain pending the case STEP.
• The library did not provide an exact EC11 footprint match during selection; ENC1 uses a PEC11R EC11-style encoder substitute and must be mechanically verified/replaced if the case requires a specific EC11 variant.
• Arduino D18/D19 were mapped using the standard ATmega32U4 Leonardo-style mapping: D18 = PF7 and D19 = PF6. The pasted text also labels them A4/A5, so firmware/mechanical documentation should verify the target board variant.

• No LEDs, displays, or RGB lighting are included because they were not specified.
• The macropad uses individual GPIO inputs rather than a row/column matrix because 12 exact Arduino pins were specified.
• Encoder A/B pull-ups may be firmware/internal pull-ups unless ERC or firmware requirements drive external pull-ups later.

• Initial specification created from the two pasted text attachments, which contained duplicate requirements.
• Schematic implemented with ATMEGA32U4-AU, USB-C, USBLC6-2SC6, 0603L050YR PTC, 16 MHz crystal, 11 Kailh MX hotswap sockets, PEC11R encoder, reset switch, 12× 1N4148W diodes, CC pull-downs, USB series resistors, decoupling, UCAP, AREF, and GND pours.
• ERC critical checks are clean; PCB has only unrouted airwires by design because routing is intentionally deferred until case STEP alignment.
• Mechanical layout updated from the user's reference photo: 3 MX switches on the top row, EC11 encoder at upper-right, 4 MX switches on the middle row, and 4 MX switches on the bottom row. USB-C remains centered at the top edge. Routing remains deferred.