How to vary pulse frequency smoothly

I have created a 1000 Hz pulse wave in Simulink using the Repeating Sequence Stair block. How can I make this pulse wave vary sinusoidally between 500Hz and 1500Hz?

Answer 1

[Shubham]

HI @優大,

As per my understanding, you are trying to create a pulse wave with a frequency that varies sinusoidally between 500Hz and 1500Hz. You're currently using a Repeating Sequence Stair block for creating a 1000 Hz pulse wave.

Here is how you can achieve your goal using MATLAB Function block:

• Use a MATLAB Function block: This block will allow you to generate a pulse wave with a frequency that varies sinusoidally. Here's a sample code snippet for the function:

function y = pulse_wave(t, freq)
% Generate a pulse wave with a frequency that varies sinusoidally
% t: Current time (input from Clock block)
% freq: Sinusoidal frequency input (in Hz)

    T = 1 / freq; % Calculate the period
    y = mod(t, T) < (T / 2); % Generate a 50% duty cycle pulse wave
end

• Add a Clock Block to provide the current simulation time
• Add a Sine Wave Block to generate the sinusoidal frequency variation. Configure its parameters: Amplitude: 500 (modulation range of ±500 Hz), Bias: 1000 (base frequency of 1000 Hz) and Frequency: (2*pi* 0.1) (0.1 Hz modulation speed)
• Connect the output of the Clock block to the first input of the MATLAB Function block.
• Connect the output of the Sine Wave block to the second input of the MATLAB Function block.

By following these steps, you will create a pulse wave whose frequency varies sinusoidally between 500 Hz and 1500 Hz.

For more information on MATLAB Function block, refer to the following documentation link:

https://mathworks.com/help/releases/R2024b/simulink/slref/matlabfunction.html

Hope this helps.

[優大]

Thank you very much.

I copied the code and put together a block diagram.

I got this in scope, but why are the frequencies not transitioning nicely?

[Shubham]

It may be due to the high frequency and the sample time of the simulation. If the sample time is not small enough to capture the high-frequency transitions accurately, the output may appear distorted.

[優大]

Thank you. I'll try it.