<!-- Braindumps capacitor code calculator: reads codes such as 104, 473J, 2A104J and 4n7, and finds the code for a value. Self-contained: no external files. -->
<div id="bd-capc">
<style>
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#bd-capc *{box-sizing:border-box}
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#bd-capc legend{font-weight:700;padding:0 6px}
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#bd-capc label{display:block;font-size:.92em;margin-bottom:10px}
#bd-capc input,#bd-capc select{width:100%;padding:9px 10px;margin-top:4px;border:1px solid var(--bd-line);border-radius:6px;font:inherit;background:transparent;color:inherit}
#bd-capc #bd-capc-code{font-size:1.25em;letter-spacing:.04em;text-transform:none}
#bd-capc select option{color:#000;background:#fff}
#bd-capc .chips{display:flex;flex-wrap:wrap;gap:6px;margin:0 0 10px}
#bd-capc .chips button{padding:5px 12px;border:1px solid var(--bd-line);border-radius:999px;background:transparent;color:inherit;font:inherit;font-size:.9em;cursor:pointer}
#bd-capc .chips button:hover{border-color:var(--bd-red)}
#bd-capc .result{border:2px solid var(--bd-red);border-radius:10px;padding:12px 16px;background:var(--bd-soft);margin:0 0 14px}
#bd-capc .big{font-size:1.6em;font-weight:700;margin:0 0 4px}
#bd-capc table{width:100%;border-collapse:collapse;margin:8px 0 0}
#bd-capc td{padding:6px 0;border-bottom:1px solid var(--bd-line)}
#bd-capc td:last-child{text-align:right;font-variant-numeric:tabular-nums;font-weight:700}
#bd-capc .warn{margin:10px 0 0;padding:8px 12px;border-left:4px solid var(--bd-red);background:var(--bd-soft);font-size:.92em}
#bd-capc details{margin-top:8px}
#bd-capc summary{cursor:pointer;font-weight:700}
#bd-capc pre{white-space:pre-wrap;font-size:.85em;margin:8px 0 0;background:transparent;border:0;padding:0}
</style>

<fieldset>
<legend>Read a code</legend>
<label>Code printed on the capacitor<input id="bd-capc-code" type="text" value="104" autocomplete="off" autocapitalize="off" spellcheck="false" placeholder="For example 104, 473J, 2A104J or 4n7"></label>
<div class="chips" aria-label="Example codes">
<button type="button" data-c="104">104</button><button type="button" data-c="473J">473J</button><button type="button" data-c="2A104J">2A104J</button><button type="button" data-c="4n7">4n7</button><button type="button" data-c="229">229</button><button type="button" data-c="106">106</button>
</div>
</fieldset>

<div class="result" aria-live="polite">
<p class="big" id="bd-capc-big"></p>
<table><tbody>
<tr><td>In picofarads</td><td id="bd-capc-pf"></td></tr>
<tr><td>In nanofarads</td><td id="bd-capc-nf"></td></tr>
<tr><td>In microfarads</td><td id="bd-capc-uf"></td></tr>
<tr><td>Tolerance</td><td id="bd-capc-tol"></td></tr>
<tr><td>Voltage rating</td><td id="bd-capc-volt"></td></tr>
</tbody></table>
<div class="warn" id="bd-capc-warn" hidden></div>
<details><summary>Show the working</summary><pre id="bd-capc-working"></pre></details>
</div>

<fieldset>
<legend>Find the code for a value</legend>
<div class="grid">
<label>Value<input id="bd-capc-val" type="number" min="0" step="any" value="4.7" inputmode="decimal"></label>
<label>Unit<select id="bd-capc-unit">
<option value="1">pF</option>
<option value="1000" selected>nF</option>
<option value="1000000">µF</option>
</select></label>
</div>
</fieldset>

<div class="result" aria-live="polite">
<p class="big" id="bd-capc-rbig"></p>
<table><tbody>
<tr><td>Three-digit code</td><td id="bd-capc-r3"></td></tr>
<tr><td>Letter code</td><td id="bd-capc-rl"></td></tr>
<tr><td>Same value in pF, nF and µF</td><td id="bd-capc-rall"></td></tr>
</tbody></table>
<div class="warn" id="bd-capc-rwarn" hidden></div>
</div>

<p class="bd-credit" style="font-size:.85em;opacity:.75;margin:10px 0 0">Capacitor code calculator by <a href="https://braindumps.co.uk/capacitor-code-calculator/">Braindumps.co.uk</a></p>
<script>
(function () {
  "use strict";
  /* BEGIN CALC */
  // Tolerance letters: KEMET (B to G, J, K, M, Z) and TDK film capacitors (H).
  var TOL = {
    B: "±0.1 pF", C: "±0.25 pF", D: "±0.5 pF", F: "±1%", G: "±2%", H: "±2.5%",
    J: "±5%", K: "±10%", M: "±20%", Z: "+80% / −20%"
  };
  // Voltage codes: Nichicon's rated voltage codes, with 2J and 3A as used on film capacitors.
  var VOLT = {
    "0E": 2.5, "0G": 4, "0L": 5.5, "0J": 6.3, "1A": 10, "1C": 16, "1D": 20, "1E": 25, "1V": 35, "1H": 50,
    "1J": 63, "1K": 80, "2A": 100, "2Q": 110, "2B": 125, "2C": 160, "2Z": 180, "2D": 200, "2P": 220,
    "2E": 250, "2F": 315, "2V": 350, "2G": 400, "2W": 450, "2H": 500, "2L": 550, "2X": 600, "2J": 630, "3A": 1000
  };
  var UNIT = { P: 1, N: 1000, U: 1e6 };
  function clean(x) { return Number(x.toPrecision(12)); }
  // Reads a marking. Returns {ok, pf, tol, volt, steps} or {ok:false, reason}.
  function decode(text) {
    var s = String(text || "").replace(/\s+/g, "").replace(/µ|μ/g, "U");
    if (!s) { return { ok: false, reason: "empty" }; }
    var steps = [], volt = null, tol = null, m;
    // A voltage written out after the code, such as 104J 100V or 4n7 50V.
    m = s.match(/(\d+(?:\.\d+)?)V$/i);
    if (m && s.length > m[0].length) {
      volt = parseFloat(m[1]);
      s = s.replace(m[0], "");
      steps.push(m[0].toUpperCase() + " = rated " + volt + " V");
    }
    // A two-character voltage code in front of a number code, such as 2A in 2A104J. It must be
    // followed by two or three digits, so that letter codes such as 2p2 (2.2 pF) are not read as one.
    m = s.toUpperCase().match(/^([0-3][A-Z])(\d{2,3}[A-Z]?)$/);
    if (m && VOLT] !== undefined) {
      volt = VOLT];
      steps.push(m[1] + " = voltage code for " + volt + " V");
      s = s.slice(2);
    }
    var up = s.toUpperCase();
    // A tolerance letter at the end, such as J in 473J.
    m = up.match(/^(.*\d)([BCDFGHJKMZ])$/);
    if (m) {
      tol = m[2];
      up = m[1];
      steps.push(tol + " = tolerance " + TOL[tol]);
    }
    var pf = null;
    if ((m = up.match(/^(\d{3})$/))) {
      var sig = parseInt(up.slice(0, 2), 10), d = parseInt(up[2], 10);
      if (d === 9) {
        pf = clean(sig * 0.1);
        steps.unshift(up + ": " + sig + " × 0.1 = " + pf + " pF (a third digit of 9 means multiply by 0.1)");
      } else if (d === 8) {
        pf = clean(sig * 0.01);
        steps.unshift(up + ": " + sig + " × 0.01 = " + pf + " pF (a third digit of 8 means multiply by 0.01)");
      } else {
        pf = clean(sig * Math.pow(10, d));
        steps.unshift(up + ": " + sig + (d === 0 ? " with no zeros" : " followed by " + d + " zero" + (d === 1 ? "" : "s")) + " = " + fmtNum(pf) + " pF");
      }
    } else if ((m = up.match(/^(\d{1,2})$/))) {
      pf = parseInt(m[1], 10);
      steps.unshift(up + ": a number with only one or two digits is the value in picofarads = " + pf + " pF");
    } else if ((m = up.match(/^(\d*)([PNU])(\d*)$/)) && (m[1] + m[3]).length > 0) {
      var num = parseFloat((m[1] || "0") + "." + (m[3] || "0"));
      pf = clean(num * UNIT]);
      var unitName = m[2] === "P" ? "pF" : m[2] === "N" ? "nF" : "µF";
      steps.unshift(text.replace(/\s+/g, "") + ": the letter stands for the unit (" + unitName + ") and sits where the decimal point goes, so " + num + " " + unitName);
    } else if ((m = up.match(/^(\d+(?:\.\d+)?)(P|N|U)F$/))) {
      pf = clean(parseFloat(m[1]) * UNIT]);
      steps.unshift("Value written out: " + m[1] + " " + (m[2] === "P" ? "pF" : m[2] === "N" ? "nF" : "µF"));
    } else if (/R/.test(up)) {
      return { ok: false, reason: "r" };
    } else {
      return { ok: false, reason: "unknown" };
    }
    if (!(pf > 0)) { return { ok: false, reason: "unknown" }; }
    return { ok: true, pf: pf, tol: tol, volt: volt, steps: steps };
  }
  // Finds the three-digit code and the letter code for a value in picofarads.
  function encode(pf) {
    if (!(pf > 0)) { return { ok: false, reason: "input" }; }
    var out = { ok: true, pf: clean(pf), code: null, letter: null, why: "" };
    var sig, d;
    if (pf < 0.1 - 1e-12) {
      out.why = "small";
    } else if (pf < 1 - 1e-12) {
      sig = Math.round(pf * 100); d = 8;
      if (Math.abs(sig - pf * 100) > 1e-6 || sig < 10) { out.why = "figures"; } else { out.code = String(sig) + d; }
    } else if (pf < 10 - 1e-12) {
      sig = Math.round(pf * 10); d = 9;
      if (Math.abs(sig - pf * 10) > 1e-6) { out.why = "figures"; } else { out.code = String(sig) + d; }
    } else {
      d = Math.floor(Math.log10(pf) + 1e-9) - 1;
      sig = Math.round(pf / Math.pow(10, d));
      if (sig >= 100) { sig = Math.round(sig / 10); d += 1; }
      if (Math.abs(sig * Math.pow(10, d) - pf) > pf * 1e-9) { out.why = "figures"; }
      else if (d > 7) { out.why = "large"; }
      else { out.code = String(sig) + d; }
    }
    // Letter code: the unit letter takes the place of the decimal point (4n7 = 4.7 nF).
    var units = [["p", 1], ["n", 1000], ["µ", 1e6]];
    var u = pf >= 1e6 ? units[2] : pf >= 1000 ? units[1] : units[0];
    var v = clean(pf / u[1]);
    var parts = String(v).split(".");
    if (parts[0].length + (parts[1] ? parts[1].length : 0) <= 3) {
      out.letter = parts[1] ? (parts[0] === "0" ? "" : parts[0]) + u[0] + parts[1] : parts[0] + u[0];
    }
    return out;
  }
  function fmtNum(x) {
    var s = String(clean(x));
    if (/e/.test(s)) { return s; }
    var p = s.split(".");
    p[0] = p[0].replace(/\B(?=(\d{3})+(?!\d))/g, ",");
    return p.join(".");
  }
  function inUnits(pf) {
    return { pf: fmtNum(pf) + " pF", nf: fmtNum(pf / 1000) + " nF", uf: fmtNum(pf / 1e6) + " µF" };
  }
  function bestUnit(pf) {
    if (pf >= 1e6) { return fmtNum(pf / 1e6) + " µF"; }
    if (pf >= 1000) { return fmtNum(pf / 1000) + " nF"; }
    return fmtNum(pf) + " pF";
  }
  /* END CALC */
  function $(id) { return document.getElementById("bd-capc-" + id); }
  function read() {
    var r = decode($("code").value), warn = $("warn");
    warn.hidden = true;
    if (!r.ok) {
      $("big").textContent = r.reason === "empty" ? "Type the code printed on the capacitor." : "That code was not recognised.";
      ["pf", "nf", "uf", "tol", "volt"].forEach(function (k) { $(k).textContent = "–"; });
      $("working").textContent = "";
      if (r.reason === "r") {
        warn.textContent = "An R marks the decimal point (2R2 = 2.2). The unit depends on the part: µF on electrolytic capacitors, pF on small ceramic ones. Check the part's datasheet.";
        warn.hidden = false;
      } else if (r.reason === "unknown") {
        warn.textContent = "Try the digits only (for example 104), a code with a letter for the unit (for example 4n7), or a full marking such as 2A104J.";
        warn.hidden = false;
      }
      return;
    }
    var u = inUnits(r.pf);
    $("big").textContent = bestUnit(r.pf) + (r.tol ? " " + TOL[r.tol] : "") + (r.volt ? ", " + r.volt + " V" : "");
    $("pf").textContent = u.pf; $("nf").textContent = u.nf; $("uf").textContent = u.uf;
    $("tol").textContent = r.tol ? TOL[r.tol] + " (" + r.tol + ")" : "not shown";
    $("volt").textContent = r.volt ? r.volt + " V" : "not shown";
    var msgs = [];
    if (r.tol && "BCD".indexOf(r.tol) >= 0 && r.pf >= 10) { msgs.push("Letters B, C and D give the tolerance in picofarads and are normally used only on values under 10 pF. Check the reading."); }
    if (r.pf >= 1e9) { msgs.push("That is 1,000 µF or more. Capacitors this large have their value printed in full: check the marking."); }
    if (msgs.length) { warn.textContent = msgs.join(" "); warn.hidden = false; }
    $("working").textContent = r.steps.join("\n") + "\n1 nF = 1,000 pF, and 1 µF = 1,000 nF = 1,000,000 pF.";
  }
  function find() {
    var val = parseFloat($("val").value), mult = parseFloat($("unit").value), w = $("rwarn");
    w.hidden = true;
    var e = encode(val * mult);
    if (!e.ok) {
      $("rbig").textContent = "Type a value above zero.";
      ["r3", "rl", "rall"].forEach(function (k) { $(k).textContent = "–"; });
      return;
    }
    $("r3").textContent = e.code || "none";
    $("rl").textContent = e.letter || "none";
    var u = inUnits(e.pf);
    $("rall").textContent = u.pf + " = " + u.nf + " = " + u.uf;
    $("rbig").textContent = e.code ? "Look for " + e.code + (e.letter ? " or " + e.letter : "") : "No three-digit code for this value";
    if (!e.code) {
      w.textContent = e.why === "figures" ? "A three-digit code holds two significant figures, so this value has no exact code. Standard capacitor values have two figures, for example 4.7 nF (472)."
        : e.why === "large" ? "Values of 1,000 µF and more have no three-digit code: such capacitors have the value printed in full."
        : "Values under 0.1 pF have no three-digit code.";
      w.hidden = false;
    }
  }
  $("code").addEventListener("input", read);
  $("val").addEventListener("input", find);
  $("unit").addEventListener("change", find);
  Array.prototype.forEach.call(document.querySelectorAll("#bd-capc .chips button"), function (b) {
    b.addEventListener("click", function () { $("code").value = b.getAttribute("data-c"); read(); });
  });
  read();
  find();
})();
</script>
</div>