rescalc.js

const NUM_STEPS = 1000;

const e24 = [1, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.7, 3, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1];
const e48 = [1, 1.05, 1.1, 1.15, 1.21, 1.27, 1.33, 1.4, 1.47, 1.54, 1.62, 1.69, 1.78, 1.87, 1.96, 2.05, 2.15, 2.26, 2.37, 2.49, 2.61, 2.74, 2.87, 3.01, 3.16, 3.32, 3.48, 3.65, 3.83, 4.02, 4.22, 4.42, 4.64, 4.87, 5.11, 5.36, 5.62, 5.9, 6.19, 6.49, 6.81, 7.15, 7.5, 7.87, 8.25, 8.66, 9.09, 9.53];
const e96 = [1, 1.02, 1.05, 1.07, 1.1, 1.13, 1.15, 1.18, 1.21, 1.24, 1.27, 1.3, 1.33, 1.37, 1.4, 1.43, 1.47, 1.5, 1.54, 1.58, 1.62, 1.65, 1.69, 1.74, 1.78, 1.82, 1.87, 1.91, 1.96, 2, 2.05, 2.1, 2.15, 2.21, 2.26, 2.32, 2.37, 2.43, 2.49, 2.55, 2.61, 2.67, 2.74, 2.8, 2.87, 2.94, 3.01, 3.09, 3.16, 3.24, 3.32, 3.4, 3.48, 3.57, 3.65, 3.74, 3.83, 3.92, 4.02, 4.12, 4.22, 4.32, 4.42, 4.53, 4.64, 4.75, 4.87, 4.99, 5.11, 5.23, 5.36, 5.49, 5.62, 5.76, 5.9, 6.04, 6.19, 6.34, 6.49, 6.65, 6.81, 6.98, 7.15, 7.32, 7.5, 7.68, 7.87, 8.06, 8.25, 8.45, 8.66, 8.87, 9.09, 9.31, 9.53, 9.76];

function calcChains(volt, ampMin, ampMax, targets, series) {
    if (targets === null)
        return [];

    var eseries = series === 'e24' ? e24 : series === 'e96' ? e96 : e48;

    if (ampMax === null || ampMin === ampMax) {
        return [calcChain(volt, ampMin, targets, eseries)];
    }

    var chains = [];
    for (var step = 0; step < NUM_STEPS; step++) {
        var curAmp = ampMin + (ampMax - ampMin) / NUM_STEPS * step;
        chains.push(calcChain(volt, curAmp, targets, eseries));
    }

    return chains.sort((a, b) => a.accuracy - b.accuracy).slice(0, 20);
}

function calcChain(volt, amp, targets, eseries) {
    var chain = {
        volt: volt,
        amp: amp,
        targets: targets,
        res: [],
        accuracy: 0,
        outs: [],
    };

    var remainingRes = volt / amp;
    var diff = 0.0;

    for (var i = 0; i < targets.length + 1; i++) {
        var nextRes;

        if (i < targets.length) {
            var ratio;

            if (i === 0) {
                ratio = targets[i] / volt;
            } else {
                ratio = targets[i] / targets[i - 1];
            }

            var idealRes = (remainingRes + diff) - ratio * (remainingRes + diff);
            nextRes = bestRes(idealRes, eseries);
            diff = (remainingRes - ratio * remainingRes) - nextRes;
        } else {
            nextRes = bestRes(remainingRes + diff, eseries);
        }

        remainingRes -= nextRes;
        chain.res.push(nextRes);
    }
    evaluate(chain);
    return chain;
}

function dist(num1, num2) {
    return Math.abs(num1 - num2);
}

function bestRes(target, eseries) {
    //index in eseries array
    var index = 0;

    //decade factor. number of digits infront of a comma/dot - 1
    var factor = target.toString().split(".")[0].length - 1;
    var currentBest = eseries[index] * Math.pow(10, factor);

    for (; index < eseries.length - 1; index++) {
        var newValue = eseries[index + 1] * Math.pow(10, factor);

        if (dist(target, currentBest) > dist(target, newValue)) {
            currentBest = newValue;
        } else {
            break;
        }
    }

    //in the case we need to wrap decade to one higher
    if (index === eseries.length - 1) {
        var newValue = eseries[0] * Math.pow(10, factor + 1);
        if (dist(target, currentBest) > dist(target, newValue)) {
            currentBest = newValue;
        }
    }

    return currentBest;
}

function evaluate(chain) {
    for (var i = 0; i < chain.res.length - 1; i++) {
        //[:i]
        var p1 = chain.res.slice(0, i + 1).reduce((a, b) => a + b, 0);
        //[i+1:]
        var p2 = chain.res.slice(i + 1, chain.res.length).reduce((a, b) => a + b, 0);
        chain.outs[i] = (chain.volt * p2) / (p1 + p2);
    }

    chain.accuracy = 0;
    for (var i = 0; i < chain.outs.length; i++) {
        var curDev = dist(chain.targets[i], chain.outs[i]);
        chain.accuracy += Math.pow(curDev, 2);
    }
    chain.accuracy = Math.sqrt(chain.accuracy);
}

export { calcChains };

export resChain to LTSpice: gist