M5Stack Money Eyes Robot 👀💰

A charming robot face animation project for M5Stack Basic featuring random eye movements, natural blinking, and sound effects when eyes transform into dollar signs! 🤖

Perfect for beginners - Detailed explanations included for those new to embedded programming!

日本語版はこちら / Japanese Version

🎯 What This Robot Does


Final setup (M5 BOTTOM not required)	The moment the “Money” sound plays

👀 Realistic Eye Movement: Eyes randomly look around like they're alive
😊 Natural Blinking: Blinks every 2-5 seconds, just like real eyes
💰 Money Mode: Eyes transform into "$" symbols every 4-8 seconds
🔊 Sound Effects: Plays cash register sound when entering money mode
📱 Firmware Display: Shows version info at startup (never forget which code you uploaded!)

🚀 Why I Built This

I was playing around with M5Stack and thought, "Wouldn't it be cool to make some fun animations?"

Initially, I tried using the built-in speaker, but the noise was terrible! 😅 Crackling, popping, and distortion everywhere.

That's when I decided to use an external I2S amplifier (MAX98357A) to achieve crystal-clear audio quality!

🛠️ Required Components

Shopping List

M5Stack Basic v2.7 (Main board)
MAX98357A I2S Amplifier Module (~$3)
Speaker (4Ω, 3W recommended) (~$2)
Jumper wires (For connections) (~$1)
microSD card (For audio storage) (~$3)

Total Budget: ~$10 💰

Prices exclude the M5Stack itself

🔌 Super Simple Wiring

Only 6 connections needed! Here's the actual wiring setup:

Actual connection photo showing the 6-wire setup

Wire Color	MAX98357A Pin	M5Stack Basic Pin	Pin Location	Purpose
🔴 Red	VIN	5V	Right column, 14th from top	Power Supply
⚫ Black	GND	GND	Left column, 3rd from top	Ground
🟡 Yellow	GAIN	GND	Left column, 2nd from top	Gain Control (0dB)
🟢 Green	DIN	G15 (IISOUT)	Left column, 12th from top	Audio Data
🟠 Orange	BCLK	G12 (IISK)	Left column, 11th from top	Bit Clock
🟤 Brown	LRC	G13 (II_WS)	Right column, 11th from top	Left/Right Clock

Important Notes:

🔴 VIN to 5V: Provides sufficient power for the amplifier
🟡 GAIN to GND: Sets gain to 9dB (moderate volume)
⚫ SD (Shutdown): Leave unconnected (defaults to enabled)
📍 Pin counting: Count from the top of each column as shown in the photo

Detailed Pin Mapping:

M5Stack Basic Pinout Reference:
Left Column:          Right Column:
1. G23               1. G1
2. GND  ← GAIN       2. G3  
3. GND  ← GND        3. G16
...                  ...
11. G12 ← BCLK       11. G13 ← LRC
12. G15 ← DIN        12. G2
13. G34              13. G5
14. G35              14. 5V  ← VIN

💻 Code Explanation (Beginner-Friendly!)

🏗️ Basic Structure

Let's start with the foundation:

// Firmware info (Important! Never forget which code you uploaded)
#define FW_NAME "Money-Eyes Robot"      // Project name
#define FW_VERSION "v1.2"               // Version number
#define FW_BUILD "I2S Audio Edition"    // Build type

// Eye positions on 320x240 screen
const int LEFT_X = 100;     // Left eye X coordinate (100px from left)
const int RIGHT_X = 220;    // Right eye X coordinate (220px from left)
const int CENTER_Y = 120;   // Eye Y coordinate (120px from top)
const int R_WHITE = 55;     // White part radius
const int R_BLACK = 20;     // Black pupil radius

Why const? → These values never change, so we protect them from accidental modification.

🎵 I2S Audio System Magic

Initially, the built-in speaker had these problems:

❌ Terrible noise (hissing sounds)
❌ Audio distortion (music sounded crushed)
❌ Crackling/popping noises (digital interference)

The Solution: I2S (Inter-IC Sound)

// I2S configuration (Digital audio communication settings)
#define I2S_SAMPLE_RATE 44100  // Sample 44,100 times per second (CD quality)
#define I2S_SAMPLE_BITS 16     // 16-bit audio data
#define I2S_CHANNELS    2      // Stereo (left + right channels)

// Pin assignment (Connecting M5Stack to MAX98357A)
#define I2S_BCK_IO  (12)  // Bit clock (audio timing signal)
#define I2S_WS_IO   (13)  // Word select (left/right channel switch)
#define I2S_DO_IO   (15)  // Data output (actual audio data)

Core Noise Reduction Strategy:

// Stop other functions that cause electrical noise
WiFi.mode(WIFI_OFF);  // WiFi radio waves cause interference
btStop();             // Bluetooth also causes noise

// Disable M5Stack's built-in speaker pins (prevent conflicts)
pinMode(25, INPUT_PULLDOWN);  // Original LRC pin → safe state
pinMode(26, INPUT_PULLDOWN);  // Original BCLK pin → safe state

🔧 DMA Buffer: The Secret to Smooth Audio

DMA (Direct Memory Access) lets audio data flow directly from memory to the speaker without using the CPU.

i2s_config_t i2s_config = {
    // ... other settings ...
    .dma_buf_count = 8,      // Number of DMA buffers (Important!)
    .dma_buf_len = 1024,     // Size of each buffer (samples)
};

Why are DMA buffers crucial?

🎵 Prevents audio dropouts: Music keeps playing even when CPU is busy
🔄 Buffer rotation: While one plays, another loads new data
📊 Right sizing: Too small = dropouts, too large = delay

Buffer calculation:

Total buffer memory = dma_buf_count × dma_buf_len × 4 bytes
Example: 8 × 1024 × 4 = 32KB

For 44.1kHz stereo:
1 second of audio = 44,100 × 2ch × 2 bytes = 176.4KB
32KB = about 0.18 seconds of buffering

How buffer rotation works:

[Buffer 1: Playing] → Speaker
[Buffer 2: Loading] ← SD card data
[Buffer 3: Empty]
...
[Buffer 8: Empty]

As playback continues...
[Buffer 2: Playing] → Speaker  
[Buffer 3: Loading] ← SD card data
[Buffer 1: Empty]   ← Ready for next data

Careful buffer initialization:

// Completely clear DMA buffers
i2s_zero_dma_buffer(I2S_NUM);
delay(100);

// Fill with silence to prevent noise
int16_t silence[2048] = {0};
for (int i = 0; i < 15; i++) {
    i2s_write(I2S_NUM, silence, sizeof(silence), &bytesWritten, 1000);
    delay(5);  // Wait between writes (Important!)
}

Why such careful initialization?

Power-on buffers contain random garbage data
This garbage causes "pop" sounds
Overwriting with silence ensures clean startup

🎭 Animation Control Secrets

Making eye movement look natural:

// Current position and target position variables
int curX = 0, curY = 0;    // Current pupil position
int tgtX = 0, tgtY = 0;    // Target pupil position

// Move 1 pixel at a time (Critical for smoothness!)
if (curX < tgtX) curX++;        // If left of target, move right 1px
else if (curX > tgtX) curX--;   // If right of target, move left 1px

if (curY < tgtY) curY++;        // If above target, move down 1px  
else if (curY > tgtY) curY--;   // If below target, move up 1px

Why 1 pixel at a time?

Jumping directly to target looks robotic and unnatural
Human eye movement is smooth and continuous
Small incremental movement creates "living" feeling

How target positions are chosen:

// When current position reaches target, set new random target
if (curX == tgtX && curY == tgtY) {
    tgtX = random(-30, 31);   // Random horizontal ±30px range
    tgtY = random(-15, 16);   // Random vertical ±15px range
}

🎨 Graphics System Tricks

Why use sprites (temporary drawing surfaces)?

TFT_eSprite spr(&M5.Lcd);        // Create off-screen canvas
spr.createSprite(320, 240);      // Same size as main screen

// Draw complete frame off-screen
spr.fillScreen(TFT_BLACK);                                    // Black background
spr.fillCircle(LEFT_X, CENTER_Y, R_WHITE, TFT_WHITE);        // Left white eye
spr.fillCircle(RIGHT_X, CENTER_Y, R_WHITE, TFT_WHITE);       // Right white eye
spr.fillCircle(LEFT_X + curX, CENTER_Y + curY, R_BLACK, TFT_BLACK);  // Left pupil

// Display entire frame at once
spr.pushSprite(0, 0);

Benefits:

No flickering during drawing
Smooth animation
No interference from partial updates

💰 Money Mode Toggle Logic

bool moneyMode = false;          // Currently in money mode?
bool prevMoney = false;          // Was in money mode last frame? (for sound control)

// Random toggle every 4-8 seconds
if (now >= nextMoney) {
    moneyMode = !moneyMode;                    // Flip true↔false
    nextMoney = now + random(4000, 8000);     // Set next toggle time
}

// Play sound only when entering money mode
if (moneyMode && !prevMoney && !soundPlayed) {
    playWAVFile();  // Play sound effect
}

Why is prevMoney needed?

Without it, sound would play every frame (disaster! 😅)
We only want sound when "entering" money mode
Comparing current vs previous state detects the transition

⏱️ Timing Control System

unsigned long nextBlink = 0;     // Next blink scheduled time
unsigned long nextMoney = 0;     // Next money mode toggle time

// Blink detection
if (millis() >= nextBlink) {
    // Execute blink
    drawEyes(curX, curY, true);   // Close eyes
    delay(120);                   // Wait 120 milliseconds
    drawEyes(curX, curY, false);  // Open eyes
    
    // Schedule next blink (random 2-5 seconds later)
    nextBlink = millis() + random(2000, 5000);
}

What is millis()? → Returns milliseconds since power-on. Perfect for timing!

📁 File Structure

project/
├── money_eyes_robot.ino    # Main program
└── cash_44_stereo.wav      # Sound effect (place on SD card root)

📁 Project Structure

M5Stack_i2s_output/
├── src/main.cpp                    # PlatformIO source (English)
├── arduino_ide/                    # Arduino IDE versions
│   ├── money_eyes_robot_jp/        # Japanese version
│   │   └── money_eyes_robot_jp.ino
│   └── money_eyes_robot_en/        # English version
│       └── money_eyes_robot_en.ino
├── audio/                          # Audio files
│   ├── README.md                   # Audio documentation
│   └── cash_44_stereo.wav         # Sound effect (OtoLogic)
├── docs/                           # Documentation
│   ├── wiring_photo.jpg           # Wiring diagram
│   └── setup_guide.md             # Setup instructions
├── README.md                       # English documentation
├── README_JP.md                   # Japanese documentation
├── .gitignore                     # Git ignore rules
└── LICENSE                        # MIT License

🚀 Step-by-Step Setup

1. Arduino IDE Configuration

Board Manager: M5Stack-Core-ESP32
Library: M5Stack by M5Stack (install via Library Manager)

2. Audio File Preparation

Download or create cash_44_stereo.wav
Format requirements: 44.1kHz, 16-bit, Stereo
Place file in SD card root directory (not in any folder!)

3. Hardware Assembly

Follow the wiring diagram above:

🔴 Red wire: VIN → 5V (sufficient power for amplifier)
⚫ Black wire: GND → GND (ground connection)
🟡 Yellow wire: GAIN → GND (sets 9dB gain level)
🟢 Green wire: DIN → G15 (audio data)
🟠 Orange wire: BCLK → G12 (bit clock)
🟤 Brown wire: LRC → G13 (left/right clock)

Wiring Tips:

Use short jumper wires to minimize noise
Double-check pin positions using the photo reference
Ensure solid connections for stable audio

4. Upload and Test

Compile in Arduino IDE
Upload to M5Stack
Insert SD card with audio file
Power on and enjoy!

😅 Problems I Encountered (& Solutions!)

1. Weird Audio During Money Mode

Symptoms: Sound distortion, crackling during $ display

Root cause: Animation drawing was interfering with audio playback

Solution:

Changed to simple blocking playback method
Increased DMA buffer size (8 buffers, 1024 samples each)
Added duplicate playback prevention flag

2. "Pop" Sound After Playback

Symptoms: Sharp "pop" noise when audio finishes

Solution: Gradual fade-out processing

// 4-stage gentle ending process
// 1. Short silence to clear buffers
// 2. Gradual DMA buffer clearing  
// 3. Additional silence for complete muting
// 4. Final DMA clear

3. Forgetting Which Firmware Was Uploaded

Symptoms: Constantly forgetting which program was running 😅

Solution: Show firmware info for 5 seconds at startup

void showFirmwareInfo() {
  M5.Lcd.printf("Firmware: %s %s", FW_NAME, FW_VERSION);
  M5.Lcd.printf("Build: %s", FW_BUILD);
  // ... detailed info display
}

🎨 Customization Ideas

Different Eye Expressions

// Angry eyes
spr.fillTriangle(LEFT_X-20, CENTER_Y-20, LEFT_X+20, CENTER_Y-20, LEFT_X, CENTER_Y-5, TFT_RED);

// Heart eyes
spr.fillCircle(LEFT_X, CENTER_Y, 15, TFT_RED);
spr.fillTriangle(LEFT_X-10, CENTER_Y-5, LEFT_X+10, CENTER_Y-5, LEFT_X, CENTER_Y+10, TFT_RED);

Multiple Sound Effects

const char* soundFiles[] = {
  "/cash_register.wav",
  "/coin_drop.wav", 
  "/cha_ching.wav"
};

Movement Adjustments

// More frequent blinking
nextBlink = now + random(1000, 3000);  // 1-3 seconds instead of 2-5

// Wider eye movement
tgtX = random(-50, 51);  // ±50px instead of ±30px

🔧 Technical Specifications

Performance Metrics

Memory Usage: ~85KB (including 75KB for sprites)
CPU Usage: <30% during normal operation
Frame Rate: ~100 FPS for smooth animation
Audio Latency: ~180ms (due to buffer size)

Audio Specifications

Sample Rate: 44.1kHz (CD quality)
Bit Depth: 16-bit
Channels: Stereo (2 channels)
Output: I2S Digital Audio
Amplifier: MAX98357A Class D

🔧 Troubleshooting Guide

No Audio Output

Check these:

MAX98357A wiring (especially power and ground connections)
Wire colors match the table above
Pin positions: count from top as shown in photo
5V power connection (not 3.3V)
Audio file exists on SD card root
File format (must be 44.1kHz/16-bit/Stereo WAV)
Serial monitor for error messages

Poor Audio Quality

Possible causes:

Unstable 5V power supply (try external power)
Long jumper wires (keep connections short)
Wrong speaker impedance (use 4Ω speaker)
GAIN setting (yellow wire to GND sets 9dB)
SD card read speed too slow

Unstable Operation

Check these:

M5Stack power capacity (USB may not provide enough current)
SD card format (use FAT32)
Code upload success (watch for upload errors)

📈 Future Development Plans

v1.3: Electronic Pop Mode 🎵
- Expression changes synchronized with music
- Beat detection for dynamic facial animations
- Multiple expression patterns for different music genres
- Real-time audio analysis for responsive reactions
v1.4: Eye Tracking Mode 👁️‍🗨️
- AI-powered eye tracking system
- Raspberry Pi integration for computer vision
- Object detection and following capabilities
- Camera-based face recognition and interaction

🎓 Educational Value

This project is perfect for learning:

Embedded Programming: Real-time systems, timing control
Digital Audio: I2S protocol, DMA buffers, sample rates
Graphics Programming: Sprite rendering, animation techniques
Hardware Interfacing: GPIO control, external amplifiers
State Machines: Mode switching, event handling

🤝 Contributing

Found a bug? Have an improvement idea? Contributions welcome!

Fork this repository
Create feature branch (git checkout -b feature/amazing-feature)
Commit changes (git commit -m 'Add amazing feature')
Push to branch (git push origin feature/amazing-feature)
Create Pull Request

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

M5Stack Community for excellent hardware and documentation
Arduino Community for the robust development ecosystem
ESP32 Documentation for comprehensive I2S guides
MAX98357A Datasheet authors for clear technical specifications
Audio Effects: OtoLogic - Free for commercial and non-commercial use (License)

📞 Support & Community

Need help? Found a bug? Want to share your build?

🐛 Report Issues: GitHub Issues
💬 Discussions: GitHub Discussions
📸 Share Builds: Tag #MoneyEyesRobot on social media!

🌟 Show Your Support

If this project helped you:

⭐ Star this repository
🐛 Report bugs you find
💡 Suggest features you'd like
📖 Improve documentation
🔀 Contribute code
📸 Share your build on social media

Made with ❤️ for makers and learners everywhere!

Happy building! 🚀

Name		Name	Last commit message	Last commit date
Latest commit History 6 Commits
arduino_ide		arduino_ide
audio		audio
docs		docs
src		src
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md
README_JP.md		README_JP.md
platformio.ini		platformio.ini

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yokoyan-robotics/m5stack-money-eyes-robot

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