diff --git a/ppg.cpp b/ppg.cpp
index 1f80a34..9ba06e6 100644
--- a/ppg.cpp
+++ b/ppg.cpp
@@ -8,6 +8,7 @@ const int FPS = 30;
 bool isDiscardData = true;
 int countDiscard = 0;
 const int DISCARD_DURATION = 5;
+const int BUFFER_DURATION = 30;
 
 int main() 
 { 
@@ -62,6 +63,22 @@ int main()
 			cv::imshow("Your Face PLS", frame);
 			if (cv::waitKey(1000.0/FPS) >= 0)
 			break;
+			
+			cv::Mat frame_forehead = frame(foreheadROI);
+			cv::Scalar avg_forehead = mean(frame_forehead);
+			
+			bool isBufferFull = false;
+			int sampleIdBuffer = 0;
+			cv::Mat greenSignal(1, FPS*BUFFER_DURATION, CV_64F);
+			if (!isBufferFull)
+			{
+				greenSignal.at<double>(0, sampleIdBuffer) = avg_forehead[1] ;
+				sampleIdBuffer++;
+				if (sampleIdBuffer == FPS*BUFFER_DURATION)
+				{
+					isBufferFull = true;
+				}
+			}
 		}
 	}
 	return 0;