MicrophoneController

A 2-button USB HID microphone controller built on the nullbits Bit-C PRO (ATmega32U4) microcontroller. Each button supports tap-to-toggle and hold-for-push-to-talk (PTT). A mode switch selects between keyboard and gamepad HID output modes. Dual LEDs reflect the active state of each microphone button.

Features

• Dual-mode HID output: Switch between keyboard (Scroll Lock / Pause keys) and gamepad (buttons 8–9) modes
• Tap-to-toggle: Press once to activate a microphone latch that persists until toggled off
• Push-to-talk (PTT): Hold a button to send a signal only while physically held; releases on button release
• LED indicators: Each button has an LED that reflects its active state
• Serial debug output: Status messages at 9600 baud

Hardware

Board

• MCU: ATmega32U4 (Arduino Leonardo-compatible)
• Board: nullbits Bit-C PRO

Wiring

Signal	Pin	Notes
Button 1	D2	Connect to GND; internal pull-up enabled
Button 2	D3	Connect to GND; internal pull-up enabled
LED 1	D4	Connect through ~220 Ω resistor to GND
LED 2	D5	Connect through ~220 Ω resistor to GND
Mode switch	D15	LOW (to GND) = keyboard mode; HIGH/floating = gamepad mode

Software requirements

Toolchain

• Arduino IDE (latest) or arduino-cli
• Board package: Arduino AVR (built-in)

Libraries

Library	Source
Keyboard	Built-in (Arduino AVR core)
HID	Built-in (Arduino AVR core)

Gamepad output uses the AVR core's HIDSubDescriptor directly — no third-party joystick library needed.

Build & upload

Using the build script (recommended)

./compile-upload.sh          # Compile and upload
./compile-upload.sh compile  # Compile only
./compile-upload.sh upload   # Upload only

The script:

• Auto-installs dfu-programmer if missing (apt or dnf)
• Compiles with custom USB identifiers (VID 0x1209, PID 0x0001)
• Uses dfu-programmer for flashing: erase → flash → reset
• Stores build artifacts in .build/

Using Arduino IDE

1. Open MicrophoneController.ino
2. Select Tools → Board → Arduino AVR Boards → Arduino Leonardo
3. Compile: Ctrl+R
4. Upload: Ctrl+U

Button behavior

Keyboard mode (Mode pin LOW)

Action	Behavior
Tap	Toggle microphone latch state; LED tracks latch
Hold (≥50 ms)	Push-to-talk: signal active only while held; clears on release

Default key assignments:

• Button 1: Scroll Lock (0xCF)
• Button 2: Pause / Break (0xE1)

Gamepad mode (Mode pin HIGH)

Action	Behavior
Tap	Toggle joystick button latch state; LED tracks latch
Hold (≥50 ms)	Push-to-talk: joystick button active only while held; clears on release

Button assignments:

• Button 1: Joystick button 8
• Button 2: Joystick button 9

Remapping keys

Keys are hardcoded compile-time constants. Edit MicrophoneController.ino:

uint8_t MIC_KEYS[2] = { KEY_SCROLL_LOCK, KEY_PAUSE };

Change to any key from Arduino's Keyboard.h (e.g. KEY_F13, KEY_F14), then recompile and upload.

Web configuration UI

A web configuration page exists in web/ (jQuery + WebUSB) but WebUSB is not yet implemented in the firmware. Keys can only be changed by editing the source and re-flashing.

Architecture

All firmware logic is in a single sketch file: MicrophoneController.ino.

Key constants

Constant	Default	Purpose
HOLD_MS	50	Milliseconds held before press is treated as PTT
DEBOUNCE_MS	10	Debounce window (ms)
MIC_KEYS[2]	{ KEY_SCROLL_LOCK, KEY_PAUSE }	Keyboard keys per button
JOY_BTN[2]	{ 7, 8 }	0-indexed joystick button slots

Button state machine

Field	Purpose
pressed	Current debounced press state
hold	True once hold threshold crossed
latch	Latched active state (toggled by tap, set/cleared by hold)
pressStart	millis() at press start
lastDebounce	millis() at last debounce check

Key functions

• setSignal(idx, active) — press/release key (keyboard) or set joystick bit (gamepad)
• setMode() — reads mode pin, switches mode if changed, releases all outputs
• handleButton(idx) — debounce, press/hold/release detection, latch management, LED update
• gamepadSetButton(index, state) — sets/clears single bit in 32-bit button state
• gamepadSend() — sends current button state as raw HID report (report ID 3)
• initVariant() — registers custom 32-button HID descriptor before USB enumeration

Serial monitor

The device prints status messages at 9600 baud:

• Mode changes: Switched to mode: keyboard

View with Arduino IDE Serial Monitor or screen /dev/ttyACM0 9600.

Troubleshooting

IntelliSense errors in VS Code / Arduino IDE

#include errors for Keyboard.h / HID.h are IntelliSense path issues only — code compiles correctly.

Fix: Command palette → Arduino: Board Config → select Leonardo → Arduino: Rebuild IntelliSense Configuration.

Device not detected during upload

1. Verify a data cable (not power-only) is used
2. Check Tools → Board → Arduino Leonardo
3. If needed: disconnect, hold reset, reconnect, upload immediately

Keys not responding

1. Check mode pin (D15) wiring
2. Test with a different application
3. Open Serial Monitor to verify mode detection
4. Check button wiring with a multimeter (should short to GND when pressed)