diff --git a/heartRateEstimation.m b/heartRateEstimation.m
index 64e35d0..3fd51f9 100644
--- a/heartRateEstimation.m
+++ b/heartRateEstimation.m
@@ -69,17 +69,30 @@ blueChannel_avg = mean(blueChannel);
 blueChannel_std = std(blueChannel);
 
 % normalize your data
-for i=1:columns(greenChannel)
+%first define length of our data
+L = columns(greenChannel);
+for i=1:L
   greenChannel_normalized(i) = (greenChannel(i) - greenChannel_avg)/greenChannel_std;
 end
 
-% fft(greenChannel_normalized)
+greenChannel_fft = fft(greenChannel_normalized);
 
 % power spectrum (https://www.mathworks.com/help/matlab/ref/fft.html)
+P2 = abs(greenChannel_fft/L);
+P1 = P2(1:L/2+1);
+P1(2:end-1) = 2*P1(2:end-1);
+f = 15*(0:(L/2))/L;
+plot(f,P1)
 
 % find the peak in the range ([0.75 4] Hz)
 % max -> value, index
 
+low_index = 0.75*L/15+0.5
+high_index = 2*L/15
+a = max(P1(low_index:high_index))
+heart_rate = f(a)
+
+
 % convert the index from Hz to bpm
 
 % determine heart rate