<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8f9fa;
      color: #1e2945;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .main-layout {
      width: 100%;
      max-width: 640px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }

    /* Signal flow track */
    .flow-grid {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 8px;
      position: relative;
    }

    .stage-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 10px 6px;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      cursor: pointer;
      transition: box-shadow 0.25s ease, border-color 0.25s ease, transform 0.2s ease;
      position: relative;
      user-select: none;
    }

    .stage-card:hover {
      box-shadow: 0 4px 12px rgba(0, 102, 204, 0.08);
    }

    .stage-card.active {
      border-color: #0066cc;
      box-shadow: 0 0 0 2px rgba(0, 102, 204, 0.25);
    }

    .stage-num {
      width: 20px;
      height: 20px;
      border-radius: 50%;
      background: #eef2f6;
      color: #64748b;
      font-size: 11px;
      font-weight: 700;
      display: flex;
      align-items: center;
      justify-content: center;
      margin-bottom: 6px;
      transition: background 0.2s, color 0.2s;
    }

    .stage-card.active .stage-num {
      background: #0066cc;
      color: #ffffff;
    }

    .stage-title {
      font-size: 12px;
      font-weight: 700;
      line-height: 1.25;
      color: #1e2945;
      min-height: 30px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .wave-box {
      width: 100%;
      height: 48px;
      margin-top: 8px;
      background: #f8fafc;
      border: 1px solid #edf2f7;
      border-radius: 6px;
      display: flex;
      align-items: center;
      justify-content: center;
      overflow: hidden;
    }

    .wave-svg {
      width: 100%;
      height: 100%;
    }

    /* Connecting arrows between cards */
    .arrow-indicator {
      position: absolute;
      right: -7px;
      top: 50%;
      transform: translateY(-50%);
      color: #0066cc;
      font-size: 11px;
      font-weight: 900;
      z-index: 2;
      background: #f8f9fa;
      border-radius: 50%;
      width: 14px;
      height: 14px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    /* Signal status display banner */
    .signal-status {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 12px 16px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 12px;
    }

    .signal-info {
      display: flex;
      flex-direction: column;
      gap: 2px;
    }

    .signal-type {
      font-size: 11px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #0066cc;
    }

    .signal-label {
      font-size: 14px;
      font-weight: 600;
      color: #1e2945;
    }

    /* Stepper controls */
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
    }

    .btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      color: #1e2945;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      user-select: none;
    }

    .btn:hover {
      border-color: #0066cc;
      color: #0066cc;
    }

    .btn:active {
      background: #f1f5f9;
    }

    .dots {
      display: flex;
      gap: 6px;
      align-items: center;
    }

    .dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: background 0.2s;
    }

    .dot.active {
      background: #0066cc;
      transform: scale(1.15);
    }

    @media (max-width: 480px) {
      .flow-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 10px;
      }
      .arrow-indicator {
        display: none;
      }
      .stage-title {
        font-size: 11px;
      }
    }
  </style>
</head>
<body>

  <div class="main-layout">
    
    <div class="flow-grid">
      
      <div class="stage-card active" data-step="0">
        <div class="stage-num">1</div>
        <div class="stage-title">Anti-Aliasing<br>Filter</div>
        <div class="wave-box">
          <svg class="wave-svg" viewBox="0 0 100 40">
            <path d="M 5,20 Q 25,2 45,20 T 85,20 T 95,20" fill="none" stroke="#0066cc" stroke-width="2" stroke-linecap="round"/>
          </svg>
        </div>
        <div class="arrow-indicator">→</div>
      </div>

      
      <div class="stage-card" data-step="1">
        <div class="stage-num">2</div>
        <div class="stage-title">Sample &<br>Hold</div>
        <div class="wave-box">
          <svg class="wave-svg" viewBox="0 0 100 40">
            
            <path d="M 6,20 H 22 V 7 H 38 V 9 H 54 V 27 H 70 V 33 H 86 V 23 H 94" fill="none" stroke="#0066cc" stroke-width="1.75"/>
            <circle cx="22" cy="7" r="2" fill="#0066cc"/>
            <circle cx="38" cy="9" r="2" fill="#0066cc"/>
            <circle cx="54" cy="27" r="2" fill="#0066cc"/>
            <circle cx="70" cy="33" r="2" fill="#0066cc"/>
            <circle cx="86" cy="23" r="2" fill="#0066cc"/>
          </svg>
        </div>
        <div class="arrow-indicator">→</div>
      </div>

      
      <div class="stage-card" data-step="2">
        <div class="stage-num">3</div>
        <div class="stage-title">Quantiser<br>(Discretise)</div>
        <div class="wave-box">
          <svg class="wave-svg" viewBox="0 0 100 40">
            
            <line x1="5" y1="8" x2="95" y2="8" stroke="#e2e8f0" stroke-width="1" stroke-dasharray="2,2"/>
            <line x1="5" y1="16" x2="95" y2="16" stroke="#e2e8f0" stroke-width="1" stroke-dasharray="2,2"/>
            <line x1="5" y1="24" x2="95" y2="24" stroke="#e2e8f0" stroke-width="1" stroke-dasharray="2,2"/>
            <line x1="5" y1="32" x2="95" y2="32" stroke="#e2e8f0" stroke-width="1" stroke-dasharray="2,2"/>
            
            <rect x="18" y="6" width="8" height="4" rx="2" fill="#0066cc"/>
            <rect x="36" y="6" width="8" height="4" rx="2" fill="#0066cc"/>
            <rect x="54" y="22" width="8" height="4" rx="2" fill="#0066cc"/>
            <rect x="72" y="30" width="8" height="4" rx="2" fill="#0066cc"/>
          </svg>
        </div>
        <div class="arrow-indicator">→</div>
      </div>

      
      <div class="stage-card" data-step="3">
        <div class="stage-num">4</div>
        <div class="stage-title">Binary<br>Encoder</div>
        <div class="wave-box">
          <svg class="wave-svg" viewBox="0 0 100 40">
            <text x="50" y="16" font-size="9" font-family="monospace" font-weight="700" fill="#0066cc" text-anchor="middle">110 · 111</text>
            <text x="50" y="29" font-size="9" font-family="monospace" font-weight="700" fill="#0066cc" text-anchor="middle">010 · 001</text>
          </svg>
        </div>
      </div>
    </div>

    
    <div class="signal-status">
      <div class="signal-info">
        <div class="signal-type" id="signalType">Stage 1 Output</div>
        <div class="signal-label" id="signalDesc">Band-limited Continuous Voltage</div>
      </div>
      <div class="signal-type" style="font-family: monospace; font-size: 13px;" id="signalRep">~ f(t) &lt; f_N</div>
    </div>

    
    <div class="controls">
      <button class="btn" id="prevBtn">←</button>
      <button class="btn" id="playBtn">⏸</button>
      <button class="btn" id="nextBtn">→</button>
      <div class="dots">
        <div class="dot active" data-step="0"></div>
        <div class="dot" data-step="1"></div>
        <div class="dot" data-step="2"></div>
        <div class="dot" data-step="3"></div>
      </div>
    </div>
  </div>

  <script>
    const stages = [
      {
        type: "Stage 1 Output",
        desc: "Band-limited Continuous Wave",
        rep: "v(t) [Analogue]"
      },
      {
        type: "Stage 2 Output",
        desc: "Discrete-Time PAM Signal",
        rep: "v(nTs) [Sampled]"
      },
      {
        type: "Stage 3 Output",
        desc: "Discrete-Voltage Levels",
        rep: "Q(n) [Rounded]"
      },
      {
        type: "Stage 4 Output",
        desc: "Serial Binary Bitstream",
        rep: "01011001... [Digital]"
      }
    ];

    let currentStep = 0;
    let timer = null;
    let isPlaying = true;

    const cards = document.querySelectorAll('.stage-card');
    const dots = document.querySelectorAll('.dot');
    const signalType = document.getElementById('signalType');
    const signalDesc = document.getElementById('signalDesc');
    const signalRep = document.getElementById('signalRep');
    const playBtn = document.getElementById('playBtn');
    const prevBtn = document.getElementById('prevBtn');
    const nextBtn = document.getElementById('nextBtn');

    function updateStage(idx) {
      currentStep = (idx + stages.length) % stages.length;
      
      cards.forEach((card, i) => {
        card.classList.toggle('active', i === currentStep);
      });

      dots.forEach((dot, i) => {
        dot.classList.toggle('active', i === currentStep);
      });

      const s = stages[currentStep];
      signalType.textContent = s.type;
      signalDesc.textContent = s.desc;
      signalRep.textContent = s.rep;
    }

    function startTimer() {
      stopTimer();
      timer = setInterval(() => {
        updateStage(currentStep + 1);
      }, 3000);
      isPlaying = true;
      playBtn.textContent = '⏸';
    }

    function stopTimer() {
      if (timer) clearInterval(timer);
      timer = null;
      isPlaying = false;
      playBtn.textContent = '▶';
    }

    cards.forEach((card, idx) => {
      card.addEventListener('click', () => {
        updateStage(idx);
        stopTimer();
      });
    });

    dots.forEach((dot, idx) => {
      dot.addEventListener('click', () => {
        updateStage(idx);
        stopTimer();
      });
    });

    prevBtn.addEventListener('click', () => {
      updateStage(currentStep - 1);
      stopTimer();
    });

    nextBtn.addEventListener('click', () => {
      updateStage(currentStep + 1);
      stopTimer();
    });

    playBtn.addEventListener('click', () => {
      if (isPlaying) {
        stopTimer();
      } else {
        startTimer();
      }
    });

    startTimer();
  </script>
</body>
</html>

Principles of Analogue-to-Digital Conversion in Audio

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      width: 100%;
      min-height: 100%;
      padding: 12px 16px;
    }

    .toolbar {
      display: flex;
      gap: 8px;
      margin-bottom: 12px;
      z-index: 10;
    }

    .btn {
      border: 1px solid #d1d5db;
      background: #f8fafc;
      color: #1e2945;
      padding: 6px 14px;
      border-radius: 20px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
      transition: background 0.2s, border-color 0.2s, color 0.2s, box-shadow 0.2s;
    }

    .btn.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(2, 132, 199, 0.35);
    }

    .svg-wrap {
      width: 100%;
      max-width: 580px;
      position: relative;
    }

    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }

    .filter-curve {
      transition: stroke-dashoffset 0.4s ease, opacity 0.3s ease;
    }

    .blocked-indicator {
      transition: opacity 0.3s ease, transform 0.3s ease;
    }

    .aliased-ghost {
      transition: opacity 0.3s ease, transform 0.3s ease;
    }
  </style>
</head>
<body>

  <div class="toolbar">
    <button id="btnFilterOn" class="btn active" onclick="setMode(true)">✓ Low-Pass Filter ON</button>
    <button id="btnFilterOff" class="btn" onclick="setMode(false)">✕ No Filter (Aliasing)</button>
  </div>

  <div class="svg-wrap">
    <svg viewBox="0 0 580 340" aria-label="Anti-Aliasing Filter Frequency Spectrum">
      <defs>
        
        <linearGradient id="passGradient" x1="0" y1="0" x2="0" y2="1">
          <stop offset="0%" stop-color="#0284c7" stop-opacity="0.25"/>
          <stop offset="100%" stop-color="#0284c7" stop-opacity="0.02"/>
        </linearGradient>

        <linearGradient id="blockedGradient" x1="0" y1="0" x2="0" y2="1">
          <stop offset="0%" stop-color="#94a3b8" stop-opacity="0.25"/>
          <stop offset="100%" stop-color="#94a3b8" stop-opacity="0.03"/>
        </linearGradient>

        <linearGradient id="ghostGradient" x1="0" y1="0" x2="0" y2="1">
          <stop offset="0%" stop-color="#ef4444" stop-opacity="0.35"/>
          <stop offset="100%" stop-color="#ef4444" stop-opacity="0.02"/>
        </linearGradient>

        <marker id="foldArrow" viewBox="0 0 10 10" refX="5" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1 L 8 5 L 0 9 z" fill="#ef4444" />
        </marker>
      </defs>

      
      
      <rect x="50" y="50" width="280" height="210" fill="#f0f9ff" rx="4" />
      
      <rect x="358" y="50" width="182" height="210" fill="#f8fafc" rx="4" />

      
      <line x1="50" y1="120" x2="540" y2="120" stroke="#e2e8f0" stroke-dasharray="3 3"/>
      <line x1="50" y1="190" x2="540" y2="190" stroke="#e2e8f0" stroke-dasharray="3 3"/>

      
      <line x1="358" y1="40" x2="358" y2="260" stroke="#dc2626" stroke-width="1.8" stroke-dasharray="4 3"/>

      
      <path d="M 50 260 Q 100 130, 150 210 T 250 170 T 320 260 Z" fill="url(#passGradient)" stroke="#0284c7" stroke-width="2"/>

      
      <g id="ultrasonicGroup">
        <path d="M 370 260 Q 420 110, 470 260 Z" fill="url(#blockedGradient)" stroke="#94a3b8" stroke-width="2" id="unwantedPeak"/>
      </g>

      
      <g id="aliasedGroup" class="aliased-ghost" style="opacity: 0; pointer-events: none;">
        <path d="M 246 260 Q 296 110, 346 260 Z" fill="url(#ghostGradient)" stroke="#ef4444" stroke-width="2" stroke-dasharray="4 2"/>
        
        <path d="M 420 100 C 420 40, 296 40, 296 95" fill="none" stroke="#ef4444" stroke-width="2" stroke-dasharray="4 3" marker-end="url(#foldArrow)"/>
        
        <rect x="235" y="70" width="120" height="22" rx="11" fill="#fee2e2" stroke="#fca5a5"/>
        <text x="295" y="85" fill="#b91c1c" font-size="11" font-weight="700" text-anchor="middle">Aliasing Distortion</text>
      </g>

      
      <g id="filterCurveGroup" class="filter-curve">
        
        <path d="M 50 65 L 325 65 C 338 65, 346 110, 352 260 L 540 260" fill="none" stroke="#00d2ff" stroke-width="6" stroke-linecap="round" opacity="0.3"/>
        <path d="M 50 65 L 325 65 C 338 65, 346 110, 352 260 L 540 260" fill="none" stroke="#0284c7" stroke-width="3" stroke-linecap="round"/>
      </g>

      
      <g id="blockedIndicator" class="blocked-indicator">
        
        <circle cx="420" cy="180" r="16" fill="#fee2e2" stroke="#ef4444" stroke-width="1.5"/>
        <line x1="411" y1="171" x2="429" y2="189" stroke="#dc2626" stroke-width="2.5" stroke-linecap="round"/>
        <line x1="429" y1="171" x2="411" y2="189" stroke="#dc2626" stroke-width="2.5" stroke-linecap="round"/>
        
        <rect x="360" y="206" width="120" height="24" rx="4" fill="#ffffff" stroke="#e2e8f0" filter="drop-shadow(0 1px 2px rgba(0,0,0,0.05))"/>
        <text x="420" y="222" fill="#dc2626" font-size="10.5" font-weight="700" text-anchor="middle">Blocked (No Aliasing)</text>
      </g>

      
      <line x1="50" y1="260" x2="545" y2="260" stroke="#1e2945" stroke-width="1.5"/>
      <line x1="50" y1="40" x2="50" y2="260" stroke="#1e2945" stroke-width="1.5"/>

      
      
      <line x1="50" y1="260" x2="50" y2="265" stroke="#1e2945" stroke-width="1.5"/>
      <text x="50" y="278" fill="#1e2945" font-size="12" font-weight="600" text-anchor="middle">0</text>

      
      <line x1="330" y1="260" x2="330" y2="265" stroke="#1e2945" stroke-width="1.5"/>
      <text x="330" y="278" fill="#1e2945" font-size="12" font-weight="600" text-anchor="middle">20 kHz</text>

      
      <line x1="358" y1="260" x2="358" y2="265" stroke="#dc2626" stroke-width="1.5"/>
      <text x="358" y="292" fill="#dc2626" font-size="11.5" font-weight="700" text-anchor="middle">22.05 kHz</text>
      <text x="358" y="306" fill="#dc2626" font-size="10" font-weight="600" text-anchor="middle">(Nyquist limit: ½ f<tspan font-size="8" dy="2">s</tspan>)</text>

      
      <line x1="535" y1="260" x2="535" y2="265" stroke="#1e2945" stroke-width="1.5"/>
      <text x="535" y="278" fill="#1e2945" font-size="11.5" font-weight="600" text-anchor="middle">44.1 kHz (f<tspan font-size="8" dy="2">s</tspan>)</text>

      
      <text x="300" y="332" fill="#1e2945" font-size="12" font-weight="600" text-anchor="middle">Frequency (kHz)</text>

      
      <text x="190" y="44" fill="#0284c7" font-size="12" font-weight="700" text-anchor="middle">Audible Band (Passband)</text>
      <text x="450" y="44" fill="#64748b" font-size="12" font-weight="600" text-anchor="middle">Ultrasonic (Stopband)</text>
    </svg>
  </div>

  <script>
    function setMode(filterOn) {
      const btnOn = document.getElementById('btnFilterOn');
      const btnOff = document.getElementById('btnFilterOff');
      const filterCurve = document.getElementById('filterCurveGroup');
      const blockedInd = document.getElementById('blockedIndicator');
      const unwantedPeak = document.getElementById('unwantedPeak');
      const aliasedGroup = document.getElementById('aliasedGroup');

      if (filterOn) {
        btnOn.classList.add('active');
        btnOff.classList.remove('active');

        filterCurve.style.opacity = '1';
        blockedInd.style.opacity = '1';
        unwantedPeak.style.opacity = '0.35';
        unwantedPeak.setAttribute('stroke-dasharray', '3 3');

        aliasedGroup.style.opacity = '0';
      } else {
        btnOff.classList.add('active');
        btnOn.classList.remove('active');

        filterCurve.style.opacity = '0.1';
        blockedInd.style.opacity = '0';
        unwantedPeak.style.opacity = '1';
        unwantedPeak.removeAttribute('stroke-dasharray');

        aliasedGroup.style.opacity = '1';
      }
    }
  </script>
</body>
</html>

ELEC-19.9

Aligned learning resources

Related diagrams