MoodLight —
HRV-Driven Ambient Intelligence

Real-time stress-detection IoT system — reads HRV from a smart ring and automatically adjusts ambient lighting & music, with zero manual input.

The Problem

Burnout and chronic stress are among today's biggest public-health risks. Students and young professionals usually notice only after it has already hurt their performance and sleep.

How It Works

Four steps from heartbeat to relaxation — zero user action required:

The MAX30102 uses PPG (measures heart rate via light on the skin) for the pulse · BLE (low-power Bluetooth) sends it to the MoodBox · PWM (rapid on/off pulsing) sets the LED's brightness/colour · UART (a simple serial link) passes the command to the speaker.

Processes in under 15 seconds · lighting + music activate at a score of 65+ · built-in false-positive check: exercise (high HRV) ≠ stress.

Under the Hood

Two components over BLE (Bluetooth): an Arduino MoodBox (C++ firmware) and an Android PWA (Vanilla JS, HTML5 Canvas), both built from scratch. The interesting part isn't the code — it's the design decisions behind it:

Roles: Hardware & firmware — solo. SW prototype — solo. Business plan (BMC — Business Model Canvas, a one-page business-model design tool, financials, UI/UX) — co-authored with a teammate.

// Personal baseline learned at startup (5-loop incremental avg)
// — not a population norm, not a fixed constant
float baselineHR = 70.0, baselineRMSSD = 35.0;

int calcStress(float hr, float rmssd) {
  float refHR = baselineReady ? baselineHR : 70.0;
  float refR  = baselineReady ? baselineRMSSD : 35.0;

  float s = 50.0
    + ((hr - refHR)  / max(refHR, 1.0f)) * 30.0   // HR contribution
    + ((refR - rmssd) / max(refR,  1.0f)) * 40.0;  // HRV weighted higher

  return constrain((int)s, 0, 100);
  // constrain() prevents negative scores during exercise (high HR + high HRV)
  // key false-positive prevention: running at 170 BPM ≠ stress
}

// Each intervention stored with timestamp, description, and stress delta
// — user sees the impact, not just a raw number
const periodsData = {
  week: {
    events: [
      { time: 'Tue 10:12', desc: 'Stress spike · light + music', delta: '-22pts' },
      { time: 'Wed 14:33', desc: 'Auto intervention',           delta: '-18pts' },
      { time: 'Fri 16:05', desc: 'Auto intervention',           delta: '-17pts' },
      { time: 'Sat 09:20', desc: 'Low stress · no intervention', delta: '—' },
    ]
  }
};

// Tapping a chart dot highlights the list item — and vice versa
// Bidirectional linking: chart → list, list → chart
function highlightEvent(idx) {
  document.querySelectorAll('.event-item').forEach((el, i) => {
    el.classList.toggle('active', i === idx);
  });
}

Competitive Advantage

The only system combining measurement + lighting + music into one automated, privacy-first product.

Business Model

Freemium: one-time hardware bundle + recurring subscription. From Year 2, B2B expansion into corporate wellness programmes.

Financial Projections

HW = hardware · EBITDA = earnings before interest, tax, depreciation & amortisation · LTV/CAC = customer lifetime value vs. cost to acquire a customer

Market Validation

Two phases: (1) a quantitative survey of the target demographic, controlled sample (Google Forms, May 2026); (2) qualitative user testing, n=5, with the SW prototype.

Market Size

Roadmap: MVP → Final Product