step amplitude change in a sine wave code Matlab

Hello. How do i create a step change in the amplitude of a sine wave. This is the code i have thus far:

I want to change the amplitude from 5 to say 10 after a few cycles like in the top fgure. Thanks for the help in advance.

Answer 1

[Sriram Tadavarty]

Hi Macyln,

I am not exactly sure as what you are looking for. Based on the figure, i see that you wanted to have different levels of sine output at different times.

Here is a small script that can help you, if thats the case:

clear all

Ts = 1e-6;
fundamental_frequency = 50;
fundamental_period = 1/fundamental_frequency;
t = 0:Ts:(fundamental_period*10-Ts);

threshold = t(floor(length(t)/2)); % Half the cycles
% You can threshold with the time index directly or for 100 samples as such, use t(100)
index = t < threshold;
v_ref_A = zeros(size(t,1),1);
v_ref_A(index) = 5*sin(2*pi*fundamental_frequency*t(index));
v_ref_A(~index) = 10*sin(2*pi*fundamental_frequency*t(~index));

plot(t,v_ref_A)

Note, this can be extended with multiple thresholds. I have provided only for a half the length cycle.

Please let me know, if this is not something you are after.

Hope this helps.

Regards,

Sriram

[Macyln Chingwena]

Hello Sriram,

Thank you so much for the help. Yes thats exactly what i was trying to generate.

I guess i wasnt thinking properly but i als managed to produce the same out. In case someone else requires a similar waveform. l also managed to do it for multiple cycles.

Here is the code:

clear all

%Initialize variables
Ts_main = 1e-6; 
fundamental_frequency = 50;
fundamental_period = 1/fundamental_frequency;
t = 0:Ts_main:(fundamental_period - Ts_main);

v1 = 5*sin(2*pi*fundamental_frequency*t); 
v2 = 10*sin(2*pi*fundamental_frequency*t);

k = 1;
number_periods = 5;
v_ref_A = zeros(1,length(t)*number_periods);


for i = 1 : length(t)*number_periods
    
    if i < length(t)*number_periods*9/20
       v_ref_A(i) = v1(k);
    else
       v_ref_A(i) = v2(k);
    end  
    
    if k < length(t)
        k = k + 1;
    else
        k = 1;
    end        
        
end 

Thank you once again foryour response.

Answer 2

[Macyln Chingwena]

clear all

%Initialize variables
Ts_main = 1e-6; 
fundamental_frequency = 50;
fundamental_period = 1/fundamental_frequency;
t = 0:Ts_main:(fundamental_period - Ts_main);

v1 = 5*sin(2*pi*fundamental_frequency*t); 
v2 = 10*sin(2*pi*fundamental_frequency*t);

k = 1;
number_periods = 5;
v_ref_A = zeros(1,length(t)*number_periods);


for i = 1 : length(t)*number_periods
    
    if i < length(t)*number_periods*9/20
       v_ref_A(i) = v1(k);
    else
       v_ref_A(i) = v2(k);
    end  
    
    if k < length(t)
        k = k + 1;
    else
        k = 1;
    end        
        
end