BioRhythm

BioRhythm is an ESP32-based wearable that transforms a live heartbeat signal into a synthesised drum performance, streamed wirelessly over Bluetooth A2DP to any speaker.

⚠️ Disclaimer BioRhythm is a creative / artistic project. It is not a medical device and must not be used to diagnose, screen for, or monitor any cardiac condition. The "intense beat" indicator reflects raw piezo signal amplitude only.

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Features

• Heart-driven percussion — piezoelectric sensors detect chest-wall vibrations; each beat triggers a synthesised kick drum.
• Motion-aware — onboard MPU6050 tracks steps and orientation.
• Visual feedback — WS2812B LED strip pulses with each detected beat.
• Wireless audio — ESP32 acts as an A2DP source and streams 16-bit stereo PCM to a paired Bluetooth speaker.

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Hardware

Component	Quantity
ESP32 development board	1
MPU6050 accelerometer + gyroscope	1
Piezoelectric vibration sensor	4
WS2812B LED strip (30 LEDs)	1
Bluetooth A2DP speaker	1

Pin configuration

Function	ESP32 pin
Piezo 1–4 (ADC1)	34, 35, 32, 33
WS2812B data	25
MPU6050 SDA / SCL	21 / 22 (default I²C)

The piezo channels use ADC1 specifically. ADC2 pins (e.g. 4, 12–15, 25–27) are unreliable when Wi-Fi or Bluetooth is active.

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Setup

1. Clone the repository:

   git clone https://github.com/<your-user>/BioRhythm.git
   cd BioRhythm

2. Open the folder in VS Code with the PlatformIO extension.

3. Set your Bluetooth speaker's name in src/main.cpp:

   constexpr const char* BT_SPEAKER_NAME = "MyBluetoothSpeaker";

   Replace MyBluetoothSpeaker with the exact name your speaker advertises (visible in your phone's Bluetooth pairing list). The ESP32 acts as the A2DP source and will scan for and connect to that sink on boot.

4. Power the speaker on before flashing so the ESP32 can discover it on first boot. auto_reconnect is enabled, so subsequent power-ons should reconnect automatically.

5. Build and upload:

   pio run -t upload
   pio device monitor

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How it works

   Piezo array (×4)      MPU6050
        │                    │
        ▼                    ▼
  ADC sampling          Accel events
        │                    │
        ▼                    ▼
   Adaptive baseline     Step debounce
   + threshold + refractory
        │
        ├─────────────► last_beat_ms (volatile, 32-bit atomic)
        │
        ▼                                  ▲
   LED feedback (FastLED)                  │
                                           │
                                  ┌────────┴────────┐
                                  │ A2DP audio task │
                                  │ on BT core      │
                                  └────────┬────────┘
                                           │
                              For each frame in callback:
                                t = samples_since_beat / 44.1 kHz
                                envelope = exp(-t · 8)
                                sample   = sin(2π · 80 · t) · envelope
                                           │
                                           ▼
                                 16-bit stereo PCM → A2DP sink

Beat detection runs an exponential moving average over the piezo signal, then thresholds the deviation against an adaptive baseline. A 400 ms refractory window prevents double-triggering. The detected timestamp is shared with the audio callback via a volatile uint32_t — aligned 32-bit loads/stores are atomic on Xtensa, so no mutex is required for this single-word state.

The audio callback re-evaluates the synthesis envelope on every sample based on the elapsed time since the most recent beat, generating a clean exponentially-decaying sine that lasts roughly 500 ms before falling below 16-bit resolution.

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Calibration

The two values most worth tuning for your build:

Constant	Effect
BEAT_THRESHOLD_DELTA	Higher = fewer false beats, may miss soft heartbeats
BASELINE_ALPHA	Closer to 1.0 = slower adaptation, more stable baseline

Open the serial monitor at 115200 baud, watch the signal= value, and set BEAT_THRESHOLD_DELTA to roughly 1.5–2× the resting noise floor.

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Troubleshooting

Symptom	Likely cause
No audio at all	BT_SPEAKER_NAME doesn't match your speaker exactly
Build error: main.cpp not found	Source must be at src/main.cpp, not repo root
Audio is silent or crackles	Confirm sensor wiring; check Serial for buffer warnings
Beats trigger constantly	Lower piezo gain or increase BEAT_THRESHOLD_DELTA
LEDs flash red and ESP32 reboots	MPU6050 not detected on I²C — check SDA/SCL and power

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License

MIT — see LICENSE.