diff --git a/lib/7segment.c b/lib/7segment.c
new file mode 100644
index 0000000..4914908
--- /dev/null
+++ b/lib/7segment.c
@@ -0,0 +1,34 @@
+#include <avr/io.h>
+#include <stdbool.h>
+
+/**
+ * Display pins should be mapped like this:
+ * a  b  c  d  e  f  g  DP
+ * 0  1  2  3  4  5  6  7
+ * 
+ * TODO pass register as parameter
+*/
+
+void set_display_raw(volatile uint8_t * header, uint8_t data) {
+    *header = data;
+}
+
+void set_display(volatile uint8_t * header, uint8_t value, bool period) {
+    uint8_t byte = period << 7;
+
+    switch(value) {
+        case 0: byte |= 0x3f; break;
+        case 1: byte |= 0x06; break;
+        case 2: byte |= 0x5b; break;
+        case 3: byte |= 0x4f; break;
+        case 4: byte |= 0x66; break;
+        case 5: byte |= 0x6d; break;
+        case 6: byte |= 0x7d; break;
+        case 7: byte |= 0x07; break;
+        case 8: byte |= 0x7f; break;
+        case 9: byte |= 0x6f; break;
+        default: byte &= 0x10000000; break;
+    }
+
+    set_display_raw(header, byte);
+}
diff --git a/lib/7segment.h b/lib/7segment.h
new file mode 100644
index 0000000..b7f65c2
--- /dev/null
+++ b/lib/7segment.h
@@ -0,0 +1,5 @@
+#include <avr/io.h>
+
+void set_display_raw(volatile uint8_t * header, uint8_t data);
+
+void set_display(volatile uint8_t * header, uint8_t value, bool period);
diff --git a/main.c b/main.c
index 543ac52..f36dc20 100644
--- a/main.c
+++ b/main.c
@@ -1,8 +1,11 @@
 #define __AVR_ATmega2560__
 #define F_CPU 16000000UL
+#define DISPLAY PORTF
 
 #include <avr/io.h>
 #include <util/delay.h>
+#include <stdbool.h>
+#include "lib/7segment.h"
 
 void main() {
 //     DDRB = 0b10000000;
@@ -15,12 +18,26 @@ void main() {
 //     }
 
     DDRF  = 0b11111111;
-    PORTF = 0b11111111;
+    DDRK  = 0b00000000;
+    PORTK = 0b00000001; // enable pull-up resistor
 
-    uint8_t a = 0;
+    uint8_t val = 0;
+
+    set_display(&PORTF, val, false);
 
     while(1) {
-        PORTF = a++;
-        _delay_ms(10);
+        loop_until_bit_is_clear(PINK, PINK0);
+
+        if (val >= 9) {
+            val = 0xff; // will overflow to 0 when incremented
+        }
+
+        set_display(&PORTF, ++val, true);
+
+        // debounce
+        _delay_ms(200);
+
+        loop_until_bit_is_set(PINK, PINK0);
+        set_display(&PORTF, val, false);
     }
 }