Recipe 8 — Electrocardiogram-Style Strip Chart¶

An ECG-style strip chart is a good example of domain-specific plot configuration: the grid spacing, colors, units, baseline, and scroll rate all work together. This recipe shows how those calls combine to produce a recognizable medical-paper display. See Plot Styles.

Recipe 8 — pink-grid ECG strip chart with a baseline

#include <ViewPoint.h>
#include <math.h>

float phase = 0.0f;

float ecgSample(float p) {
    if (p < 0.10f) return 0.15f * sinf((p / 0.10f) * PI);
    if (p < 0.16f) return 0.0f;
    if (p < 0.18f) return -0.10f * sinf(((p - 0.16f) / 0.02f) * PI);
    if (p < 0.22f) return 1.20f * sinf(((p - 0.18f) / 0.04f) * PI);
    if (p < 0.24f) return -0.20f * sinf(((p - 0.22f) / 0.02f) * PI);
    if (p < 0.40f) return 0.05f;
    if (p < 0.56f) return 0.30f * sinf(((p - 0.40f) / 0.16f) * PI);
    return 0.0f;
}

void setup() {
    view.begin();
    view.setDelay(4);
    view.setTitle("Heartbeat ECG");
    view.setPlotTitle("Lead II");
    view.setAxisLabels("Time", "Voltage");
    view.setUnits("s", "mV");
    view.setVerticalRange(-0.5, 1.5, 0.1, 0.5);
    view.setGridColors(0xFFCCCC, 0xFF6666);
    view.addHorizontalReferenceLine(0.0f);
    view.trace("Lead II").setColor(0x00AA00);
}

void loop() {
    view.addData("Lead II", ecgSample(phase));
    view.send();
    phase += 0.0048f;
    if (phase >= 1.0f) phase -= 1.0f;
}

What the functions do

setVerticalRange(-0.5, 1.5, 0.1, 0.5) creates the small and large divisions expected on ECG plots.
setGridColors(0xFFCCCC, 0xFF6666) gives the plot the medical paper look.
addHorizontalReferenceLine(0.0f) marks the isoelectric baseline.

When to use this

Adjust the vertical range when your signal is not in millivolts.
Change setDelay() and the phase increment together if you want a faster or slower sweep.