diff --git a/lib/7segment.c b/lib/7segment.c
index 4914908..1e99749 100644
--- a/lib/7segment.c
+++ b/lib/7segment.c
@@ -6,29 +6,33 @@
  * a  b  c  d  e  f  g  DP
  * 0  1  2  3  4  5  6  7
  * 
- * TODO pass register as parameter
+ * d1 d2 d3 d4
+ * 1  2  3  4
 */
 
 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;
+uint8_t digit_to_binary(uint8_t input, uint8_t digit) {
+    switch(digit) {
+        case 0: return input | 0x3f;
+        case 1: return input | 0x06;
+        case 2: return input | 0x5b;
+        case 3: return input | 0x4f;
+        case 4: return input | 0x66;
+        case 5: return input | 0x6d;
+        case 6: return input | 0x7d;
+        case 7: return input | 0x07;
+        case 8: return input | 0x7f;
+        case 9: return input | 0x6f;
+        // by default only draw the period if it was provided in the input
+        default: return input & (uint8_t) 0x10000000;
     }
+}
+
+void set_display(volatile uint8_t * header, uint8_t value, bool period) {
+    uint8_t byte = digit_to_binary(period << 7, value);
 
     set_display_raw(header, byte);
 }
diff --git a/lib/7segment.h b/lib/7segment.h
index b7f65c2..7a816ec 100644
--- a/lib/7segment.h
+++ b/lib/7segment.h
@@ -3,3 +3,5 @@
 void set_display_raw(volatile uint8_t * header, uint8_t data);
 
 void set_display(volatile uint8_t * header, uint8_t value, bool period);
+
+uint8_t digit_to_binary(uint8_t in, uint8_t digit);
diff --git a/lib/7segment_4digits.c b/lib/7segment_4digits.c
new file mode 100644
index 0000000..e4d24ed
--- /dev/null
+++ b/lib/7segment_4digits.c
@@ -0,0 +1,47 @@
+#include <avr/io.h>
+#include <stdbool.h>
+#include <util/delay.h>
+#include <math.h>
+#include "util.h"
+#include "7segment.h"
+
+uint8_t display[4] = { 0, 0, 0, 0 };
+
+/**
+ * Display pins should be mapped like this:
+ * a  b  c  d  e  f  g  DP
+ * 0  1  2  3  4  5  6  7
+ * 
+ * 
+*/
+
+void display_value(uint8_t digit, uint8_t data) {
+    // The left part sets the last 4 bits high (turns the
+    // according digit off) except for the one we want to address.
+    // The right part makes sure the first 4 bits remain unchanged.
+    PORTK = (0b00001111 & ~(1 << digit)) | (PORTK & 0b11110000);
+
+    PORTF = data;
+}
+
+void set_display_value(uint8_t digit, uint8_t data) {
+    display[digit] = data;
+}
+
+void update_display() {
+    for (int i = 0; i < 4; i++) {
+        display_value(i, display[i]);
+        _delay_us(100);
+    }
+}
+
+void show_float(float value) {
+    int digits = num_digits((int)value);
+    int full_number = value * (int)roundf(powf(10, 4 - digits));
+
+    for (int i = 0; i < 4; i++) {
+        bool show_period = digits == i + 1;
+        int digit = get_digit_at_position(full_number, 3 - i);
+        set_display_value(i, digit_to_binary(show_period << 7, digit));
+    }
+}
diff --git a/lib/7segment_4digits.h b/lib/7segment_4digits.h
new file mode 100644
index 0000000..ae54034
--- /dev/null
+++ b/lib/7segment_4digits.h
@@ -0,0 +1,9 @@
+#include <avr/io.h>
+
+void display_value(uint8_t digit, uint8_t data);
+
+void set_display_value(uint8_t digit, uint8_t data);
+
+void update_display();
+
+void show_float(float value);
diff --git a/lib/util.c b/lib/util.c
new file mode 100644
index 0000000..6bcd929
--- /dev/null
+++ b/lib/util.c
@@ -0,0 +1,31 @@
+int num_digits(int num) {
+    if (num < 0) num = -num;
+    if (num >= 10) return num_digits(num / 10) + 1;
+    return 1;
+}
+
+int get_digit_at_position(int number, int index) {
+    if (index < 0) {
+        return -1;
+    }
+    
+    int divisor = 1;
+    int tempNumber = number;
+    while (tempNumber >= 10) {
+        tempNumber /= 10;
+        divisor *= 10;
+    }
+    
+    if (index >= divisor) {
+        return -1;
+    }
+    
+    for (int i = 0; i < index; i++) {
+        number /= 10;
+    }
+    
+    int digit = number % 10;
+    
+    return digit;
+}
+
diff --git a/lib/util.h b/lib/util.h
new file mode 100644
index 0000000..f0a7c25
--- /dev/null
+++ b/lib/util.h
@@ -0,0 +1,3 @@
+int num_digits(int num);
+
+int get_digit_at_position(int number, int index);
diff --git a/main.c b/main.c
index bcede98..51e7fb0 100644
--- a/main.c
+++ b/main.c
@@ -5,9 +5,15 @@
 #include <avr/io.h>
 #include <util/delay.h>
 #include <stdbool.h>
+#include "lib/util.h"
 #include "lib/7segment.h"
+#include "lib/7segment_4digits.h"
 
 void main() {
+    prog_7segment_4digit();
+}
+
+void prog_7segment() {
     DDRF  = 0b11111111;
     DDRK  = 0b00000000;
     PORTK = 0b00000001; // enable pull-up resistor
@@ -32,3 +38,18 @@ void main() {
         set_display(&PORTF, val, false);
     }
 }
+
+void prog_7segment_4digit() {
+    DDRF = 0b11111111;
+    DDRK = 0b00001111;
+
+    float num = 0.0f;
+
+    while(1) {
+        show_float(num);
+        update_display();
+
+        num += 0.001f;
+        if (num >= 10000) num = 0.0f;
+    }
+}