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## Use Peak Finder to Find Heart Rate from ECG Input

This example shows how to use the Time Scope Peak Finder panel to measure the heart rate from an ECG.

This model emulates an ECG heart rate. To emulate a heart beat, the model imports the variable `mhb` from the MATLAB® workspace. This variable is created when the model loads because the commands that construct it are in the model Preload function. To view these commands, in the Simulink® menu, select `File > Model Properties > Model Properties`. The Model Properties dialog box appears. Click the `Callbacks` tab. The following lines of MATLAB® code appear.

```x1 = 3.5*ecg(2700); y1 = sgolayfilt(kron(ones(1,13),x1),0,21); n = (1:30000)'; del = round(2700*rand(1)); mhb = y1(n + del); ts = 0.00025;```

`ecg` is a custom function that helps generate the heartbeat signal.

```function x = ecg(L) a0 = [0, 1, 40, 1, 0, -34, 118, -99, 0, 2, 21, 2, 0, 0, 0]; d0 = [0, 27, 59, 91, 131, 141, 163, 185, 195, 275, 307, 339, 357, 390, 440]; a = a0 / max(a0); d = round(d0 * L / d0(15)); d(15) = L; for i = 1:14 m = d(i) : d(i+1) - 1; slope = (a(i+1) - a(i)) / (d(i+1) - d(i)); x(m+1) = a(i) + slope * (m - d(i)); end ```

Run your model to see the time domain output.

1. To show the `Peak Finder` panel, in the Time Scope menu, select `Tools > Measurements > Peak Finder`.

2. To expand the `Settings` section, click the arrow next to the label.

3. Enter 10 for `Max Num of Peaks`. The Time Scope Peaks section now displays a list of 10 peak amplitude values, and the times at which they occur. The list of peak values show a constant time difference of 0.675 seconds between each heartbeat. Therefore, the heart rate of the ECG signal is 88.89 beats per min (bpm).

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