l7 dsp

function [] = dft()

% 1 sin-wave 10Hz, amp 15, phase angle -pi/4
% 1 sin-wave 30Hz, amp 20
% 1 sin-wave 70Hz, amp 35, phase angle 3pi/4

Fs = 1000; % samples per second
dT = 1/Fs; % seconds per sample
stopTime = 0.2;
t = (0:dT:stopTime-dT)';

Fc1 = 10;
Fc2 = 30;
Fc3 = 70;
amp1 = 15;
amp2 = 20;
amp3 = 35;
phaseAngle1 = (-pi / 4);
phaseAngle3 = ((3 * pi) / 4);

y1 = amp1 * sin(2 * pi * Fc1 * t + phaseAngle1);
y2 = amp2 * sin(2 * pi * Fc2 * t);
y3 = amp3 * sin(2 * pi * Fc3 * t + phaseAngle3);

% figure;
% plot(t,y1);
% xlabel('Time (s)');
% title('First wave vs time');
%
% figure;
% plot(t,y2);
% xlabel('Time (s)');
% title('Second wave vs time');
%
% figure;
% plot(t,y3);
% xlabel('Time (s)');
% title('Third wave vs time');

S = y1 + y2 + y3;

figure;
plot(t,S);
xlabel('Time (s)');
ylabel('Amplitude');
title('Input wave vs time');

S_fft = fft(S);

for i = 1:length(S_fft)
    if (abs(S_fft(i)) < (10 ^ (-5)))
        S_fft(i) = 0;
    end
end

freq = ((0:length(S_fft)-1) * Fs) / length(S_fft);

figure;
plot(freq,abs(S_fft));
xlabel('Frequency (Hz)');
ylabel('Magnitude');
title('FFT magnitude');

figure;
plot(freq,angle(S_fft));
xlabel('Frequency (Hz)');
ylabel('Phase');
title('FFT phase');

zoom xon;
end