diff --git a/main.c b/main.c
index a46a2a8..e2e2f12 100644
--- a/main.c
+++ b/main.c
@@ -30,6 +30,11 @@ uint32_t gSystemClock; // [Hz] system clock frequency
 volatile uint32_t gTime = 0; // time in hundredths of a second
 volatile uint8_t drawRequested = 1;
 
+// assumming square lcd
+#define HEIGHT LCD_VERTICAL_MAX
+#define WIDTH LCD_HORIZONTAL_MAX
+#define PIXELS_PER_DIV 20
+
 // start a pwm test signal
 void start_signal() {
   // configure M0PWM2, at GPIO PF2, BoosterPack 1 header C1 pin 2
@@ -96,9 +101,6 @@ int main(void) {
         GrContextForegroundSet(&sContext, ClrBlack);
         GrRectFill(&sContext, &rectFullScreen); // fill screen with black
         
-        // assumming square lcd
-        #define HEIGHT LCD_VERTICAL_MAX
-        #define PIXELS_PER_DIV 20
 
         GrContextForegroundSet(&sContext, ClrBlue);
 
@@ -119,7 +121,9 @@ int main(void) {
         int32_t adc_current_index;
         int32_t j;
         if (drawRequested) {
-            adc_current_index = gADCBufferIndex - 128;
+            int trigger = RisingTrigger();
+
+            adc_current_index = trigger - (WIDTH / 2);
             for (j=0; j<LOCAL_BUF_LEN; j++) {
                 local_adc_buffer[j] = gADCBuffer[ADC_BUFFER_WRAP(adc_current_index + j)];
             }
@@ -184,3 +188,18 @@ int main(void) {
         GrFlush(&sContext); // flush the frame buffer to the LCD
     }
 }
+
+int RisingTrigger(void) // search for rising edge trigger
+{
+    #define ADC_OFFSET 20
+    int x = gADCBufferIndex - (WIDTH / 2); // half screen width
+    int x_stop = x - ADC_BUFFER_SIZE/2;
+    for (; x > x_stop; x--) {
+    if ( gADCBuffer[ADC_BUFFER_WRAP(x)] >= ADC_OFFSET &&
+        gADCBuffer[ADC_BUFFER_WRAP(x-1)] < ADC_OFFSET)
+        break;
+    }
+    if (x == x_stop) // for loop ran to the end
+    x = x = gADCBufferIndex - (WIDTH / 2); // reset x back to how it was initialized
+    return x;
+}