diff --git a/buttons.c b/buttons.c
index bc01f51..22eb0b4 100644
--- a/buttons.c
+++ b/buttons.c
@@ -28,6 +28,7 @@ uint32_t gADCSamplingRate;      // [Hz] actual ADC sampling rate
 // imported globals
 extern uint32_t gSystemClock;   // [Hz] system clock frequency
 extern volatile uint32_t gTime; // time in hundredths of a second
+extern volatile uint8_t drawRequested;
 
 // initialize all button and joystick handling hardware
 void ButtonInit(void)
@@ -189,6 +190,9 @@ void ButtonISR(void) {
     if (presses & 2) { // EK-TM4C1294XL button 2 pressed
         gTime = 0;
     }
+    if (presses & 4) { // boosterpack button 1 pressed
+        drawRequested = 1;
+    }
     if (running) {
         if (tic) gTime++; // increment time every other ISR call
         tic = !tic;
diff --git a/main.c b/main.c
index f8e7cd9..2b877bf 100644
--- a/main.c
+++ b/main.c
@@ -15,18 +15,20 @@
 #include "driverlib/interrupt.h"
 #include "Crystalfontz128x128_ST7735.h"
 #include <stdio.h>
-#include "buttons.h"
 #include "grlib/grlib.h"
-#include "sampling.h"
 #include <math.h>
+#include <string.h>
 #include "inc/hw_memmap.h"
 #include "driverlib/gpio.h"
 #include "driverlib/pwm.h"
 #include "driverlib/pin_map.h"
+#include "sampling.h"
+#include "buttons.h"
 #define PWM_FREQUENCY 20000 // PWM frequency = 20 kHz
 
 uint32_t gSystemClock; // [Hz] system clock frequency
 volatile uint32_t gTime = 0; // time in hundredths of a second
+volatile uint8_t drawRequested = 1;
 
 // start a pwm test signal
 void start_signal() {
@@ -87,8 +89,8 @@ int main(void) {
 
         GrContextForegroundSet(&sContext, ClrBlue);
 
-        uint8_t xy_pos;
         // draw gridlines from the center out
+        uint8_t xy_pos;
         for (xy_pos = HEIGHT/2; xy_pos < HEIGHT; xy_pos += PIXELS_PER_DIV) {
             GrLineDrawV(&sContext, xy_pos, 0, 128); // right
             GrLineDrawV(&sContext, HEIGHT - xy_pos, 0, 128); // left
@@ -98,7 +100,48 @@ int main(void) {
         }
 
 
+        // display graph
+        #define LOCAL_BUF_LEN 128
+        uint16_t local_adc_buffer[LOCAL_BUF_LEN]; // copy of adc buffer
+        int32_t adc_current_index;
+        int32_t j;
+        if (drawRequested) {
+            IntMasterDisable(); // critical section
+            adc_current_index = gADCBufferIndex - 128;
+            for (j=0; j<LOCAL_BUF_LEN; j++) {
+                local_adc_buffer[j] = gADCBuffer[ADC_BUFFER_WRAP(adc_current_index + j)];
+            }
+            IntMasterEnable();
+            drawRequested = 0;
+        }
 
+        GrContextForegroundSet(&sContext, ClrPink);
+        for(j=0; j<LOCAL_BUF_LEN; j++) {
+            #define TRANSPOSE(x) (HEIGHT/2) - (x >> 8)
+            //GrPixelDraw(&sContext, j, TRANSPOSE(local_adc_buffer[j]));
+            uint32_t upper,lower, current, last;
+
+            if (j==0) {
+                upper = TRANSPOSE(local_adc_buffer[j]);
+                lower = upper;
+                last = upper;
+            } else {
+                current = TRANSPOSE(local_adc_buffer[j]);
+                
+                // couldn't find these anywhere
+                #define MIN(a,b) (((a)<(b))?(a):(b))
+                #define MAX(a,b) (((a)>(b))?(a):(b))
+
+                upper = MAX(current, last);
+                lower = MIN(current, last);
+
+                last = current;
+            }
+
+            GrLineDrawV(&sContext, j, lower, upper);
+        }
+
+        // display time
         time = gTime; // read shared global only once
 
         uint32_t hundredths = time % 100;
diff --git a/sampling.c b/sampling.c
index 96093c8..c03fb79 100644
--- a/sampling.c
+++ b/sampling.c
@@ -13,12 +13,7 @@
 #include "buttons.h"
 #include "sampling.h"
 
-// index wrapping macro
-#define ADC_BUFFER_WRAP(i) ((i) & (ADC_BUFFER_SIZE - 1))
 // latest sample index
-volatile int32_t gADCBufferIndex = ADC_BUFFER_SIZE - 1;
-volatile uint16_t gADCBuffer[ADC_BUFFER_SIZE]; // circular buffer
-volatile uint32_t gADCErrors = 0; // number of missed ADC deadlines
 void ADC_ISR(void)
 {
     // clear ADC1 sequence0 interrupt flag in the ADCISC register
@@ -37,6 +32,9 @@ void ADC_ISR(void)
 
 
 void start_sampler() {
+    gADCBufferIndex = ADC_BUFFER_SIZE - 1;
+    gADCErrors = 0;
+
     SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
     GPIOPinTypeADC(GPIO_PORTE_BASE,
                     GPIO_PIN_0); // GPIO setup for analog input AIN3
diff --git a/sampling.h b/sampling.h
index 69ea810..06ea538 100644
--- a/sampling.h
+++ b/sampling.h
@@ -5,6 +5,13 @@
 
 #define ADC_BUFFER_SIZE 2048 // size must be a power of 2
 
+// index wrapping macro
+#define ADC_BUFFER_WRAP(i) ((i) & (ADC_BUFFER_SIZE - 1))
+
+volatile int32_t gADCBufferIndex;
+volatile uint16_t gADCBuffer[ADC_BUFFER_SIZE]; // circular buffer
+volatile uint32_t gADCErrors; // number of missed ADC deadlines
+
 // initialize ADC and ISR
 void start_sampler(void);