Galaga Sounds

A faithful emulation of the Namco Galaga arcade game sound chip, implemented for Arduino and PIC18 microcontrollers.

Overview

This project recreates the complete sound palette of the classic 1981 Galaga arcade cabinet using the original Namco wavetable data and synthesis parameters. It supports all 24 sounds from the game, including special effects like the explosion and electronic noise synthesis.

Features:

• 24 authentic Galaga sound effects (0-23)
• 3-voice polyphonic synthesis
• Original Namco wavetable data
• Two audio output modes (PWM DAC or resistor DAC)
• 62.5 kHz sample rate audio synthesis
• Serial-based sound triggering
• Minimal hardware requirements

Hardware

Arduino Implementation

Microcontroller: Arduino Uno or compatible (ATmega328P)

Audio Output Options:

Option 1: PWM DAC (Pin D11)

• Simplest and most universal approach
• Uses Timer2 PWM (~62.5 kHz carrier, 8-bit resolution)
• Low-pass filter recommended:
  • Resistor: 10 kΩ (series from D11)
  • Capacitor: 10 nF (to ground)
  • Cutoff: ~1.6 kHz
• Optional larger capacitor (22 nF) for smoother/warmer sound

Option 2: 6-bit Resistor DAC (Pins D2-D7)

• Binary-weighted resistor network (Namco-style)
• Recommended resistor values (MSB → LSB):
  • D2 → 4.7 kΩ
  • D3 → 2.2 kΩ
  • D4 → 1.0 kΩ
  • D5 → 470 Ω
  • D6 → 220 Ω
  • D7 → 100 Ω or 120 Ω
• All resistors sum at a single node
• Optional 1-4.7 nF smoothing capacitor from output to ground

Select output mode in code via #define AUDIO_OUT_MODE:

• AUDIO_OUT_PWM_D11 (default)
• AUDIO_OUT_R2R_6BIT_D2_D7

PIC18 Implementation

Source code provided for PIC18F4520 microcontroller:

• src/PIC18F4520/galaga.asm - Main sound engine
• src/PIC18F4520/sound.asm - Audio synthesis
• src/PIC18F4520/pacman.asm - Related implementation

Usage

Serial Interface

Connect via USB/Serial at 115,200 baud.

Commands:

• 0-23 or 0x00-0x17 - Play sound (hex or decimal)
• stop or ` - Stop all sounds
• Enter (empty line) - Repeat last sound
• m0-7 - Set voice output mask (debug, bitmask for v0/v1/v2)
• d0 / d0s - Toggle logging for sound 0 (debug)

Examples:

15       Play sound 15 (Shooting)
0x0A     Play sound 10 (Extra Life)
stop     Stop all sounds

Supports both newline-terminated and raw digit input (auto-triggers after 2 digits).

Sound Reference

#	Name	Description
0	Ambience	Background hum
1	Hit Capture Ship	Red target hit
2	Hit Red Ship	Enemy destroyed
3	Hit Blue Ship	Enemy destroyed
4	Hit Capture/Green	Mixed ship hit
5	Tractor Beam	Beam start
6	Tractor Beam Capture	Beam loops
7	Fighter Destroyed	Game over tone
8	Credit	Insert coin
9	Fighter Captured	Player captured
10	Extra Life	Bonus awarded
11	Game Start	Game beginning
12	Name Entry (1st)	High score entry
13	Challenge Start	Wave intro
14	Challenge Results	Wave end with echo
15	Shooting	Player fire
16	Name Entry (2nd-5th)	Score entry 2-5
17	Fighter Rescued	Tractor beam rescue
18	Free Life/Triple	Bonus formation
19	Enemy Flying	Ambient UFO
20	Challenge Perfect	Perfect wave bonus
21	Stage Flag	Stage marker
22	Name Entry End	High score complete
23	Explosion	Noise (custom)

Technical Details

Architecture

• Audio sampling rate: 62.5 kHz (Timer1 CTC @ 16 MHz / 256)
• Scheduler: 120 Hz game tick (updates synthesizer state)
• Voice synthesis:
  • 16-bit phase accumulator per voice
  • Wavetable lookup with volume envelope
  • Automatic phase/frequency scaling
  • Mix and quantize to 4-bit for authentic "crunch"
• Volume quantization: 4-bit per voice, 6-bit output DAC

Compilation

Define Custom Output Mode:

# (Use ARDUINO_OUT_MODE compiler flag or edit galaga_sounds_pwm_or_r2r_configurable.ino)
Arduino IDE: Sketch → Properties → Compiler options → Custom flags

Notable Implementations

• Sound 0 (Ambience): Continuous frequency sweep using lookup tables
• Sound 5 & 6 (Tractor Beam): Looping with automatic volume/waveform cycling
• Sound 14 (Echo): Progressive 3-voice echo effect (voices enabled sequentially)
• Sound 23 (Explosion): Brown noise with envelope decay (not in original tables, custom tuned)
• Sound 10 (Extra Life): Multi-voice with envelope alignment and tail fade

ROM Data

Original Galaga waveform and frequency tables extracted from arcade hardware:

• Wavetable PROM: 256-byte lookup (4-bit unipolar samples)
• Frequency table: 13 base frequencies with octave shifts
• Script sequences: 1907 bytes of voice control data

Files

.
├── README.md                         # This file
├── LICENSE                           # GNU General Public License v3
├── src/
│   ├── arduino/
│   │   ├── galaga_sounds_pwm_or_r2r_configurable/
│   │   │   └── galaga_sounds_pwm_or_r2r_configurable.ino
│   │   └── game_sounds_trigger/
│   │       └── game_sounds_trigger.ino
│   └── PIC18F4520/
│       ├── galaga.asm
│       ├── pacman.asm
│       └── sound.asm
└── reference/
    ├── galaga wavetables/
    ├── PIC18F4520_PinOut.html
    └── [Web references to Galaga docs]

Building and Flashing

Arduino

1. Open src/arduino/galaga_sounds_pwm_or_r2r_configurable/galaga_sounds_pwm_or_r2r_configurable.ino in Arduino IDE
2. Configure audio output mode (search for #define AUDIO_OUT_MODE)
3. Select board: Arduino Uno
4. Select port (e.g., /dev/cu.usbserial-xxx)
5. Click Upload

PIC18F4520

Use a PIC programmer with MPLAB IDE or compatible assembler:

gpasm -p 18f4520 galaga.asm

Requires PIC18 development environment (ICD3/ICD4 programmer or equivalent).

Attribution

• Original concept: Namco sound chip (1981 Galaga arcade)
• PIC18 reference: Fred Vecoven's Pacsound project
• Arduino port & PWM/DAC implementations: Modern adaptation with extended features
• Wavetable data: From original Galaga arcade ROM

License

GNU General Public License v3.0 - See LICENSE file for details.

Notes

• The explosion sound (23) is a custom implementation, not from original arcade tables
• Audio feeds high-impedance input (amp/powered speaker); do not drive speakers directly
• Volume is applied in software and quantized back to 4-bit for authentic crunchy character
• Pitch scaling matches original (increment multiplied by 393/256 ≈ 1.535×)