Creating a heart rate monitor

Question

I have been trying to create a heart rate monitor with chart.js, but I'm at odds as how to represent the graph.

I want to build something along the lines of this demonstration: link to demo.

The charts in chart.js are made like this:

var data = {
    labels: ["Heart Rate Monitor"],
    datasets: [
        {
            label: "heart rate",
            data: [65, 59, 80, 81, 56, 55, 40]
        }
    ]
};

var myLineChart = new Chart(ctx).Line(data, {});

And we can update the data like this:

myLineChart.datasets[0].points[0].value = 50;

Which would set the first value in the array: 65, to 50.

So I have made some attempts at creating an array with values that look like the demo, and move the first element to last, and every other element one down (-1) on the array and fill the chart with the values. This works, to a certain extent, but I am not able to change the speed of the values, which I need to do.

Suggestions?

potatopeelings · Accepted Answer

You could use 2 series and just swap in the points. You might need to interpolate between points to smoothen out the animation.

I've used linear interpolation, but for a smoother curve you could probably use something else, but I believe if you have actual data, linear interpolation would work fine.

function getActualData() {
    var actualData = []
    for (var m = 0; m < 20; m++)
        actualData.push(45 + parseInt(Math.random() * 35))
    return actualData;
}


var ANIMATIONSTEPS = 200;

var myLineChart;
var labels;
var animationStep;
setInterval(function () {
    if (myLineChart === undefined) {
        var actualData = getActualData();

        // if we have only a few data points interpolate to fill out enough points to make the animation smooth
        var interpolationSteps = Math.ceil(ANIMATIONSTEPS / actualData.length);
        labels = []
        var data = []
        var blankData = []
        for (var i = 0; i < (actualData.length - 1); i++) {
            labels.push('')
            data.push(actualData[i])
            blankData.push(null)

            // push interpolation
            var difference = actualData[i + 1] - actualData[i];
            var interpolationStep = 1 / interpolationSteps;
            for (var j = 1; j < interpolationSteps; j++) {
                labels.push('')
                data.push(actualData[i] + difference * Chart.helpers.easingEffects["linear"](j * interpolationStep));
                blankData.push(null)
            }
        }
        labels.push('')
        data.push(actualData[i])
        blankData.push(null)

        var data = {
            labels: labels,
            datasets: [
                {
                    strokeColor: "rgba(243, 118, 27, 1)",
                    data: blankData
                },
                {
                    strokeColor: "transparent",
                    data: data
                }
            ]
        };

        var ctx = document.getElementById("myChart").getContext("2d");
        myLineChart = new Chart(ctx).Line(data, {
            animation: false,
            datasetFill: false,
            pointDot: false,
            datasetStrokeWidth: 5,
            showTooltips: false,
            scaleOverride: true,
            scaleSteps: 12,
            scaleStepWidth: 5,
            scaleStartValue: 30,
            scaleShowVerticalLines: false,
            scaleShowLabels: false,
        });

        animationStep = 0;
    }

    // the actual animation
    myLineChart.datasets[0].points[animationStep].value = myLineChart.datasets[1].points[animationStep].value
    myLineChart.update();
    animationStep++;

    // start new cycle
    if (animationStep >= labels.length) {
        myLineChart.destroy();
        myLineChart = undefined;
    }
}, 10)

Fiddle - http://jsfiddle.net/t795k4j3/

Creating a heart rate monitor

Answers (2)

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