diff --git a/module01/ex03/main.c b/module01/ex03/main.c
index 77d3636..ba36f08 100644
--- a/module01/ex03/main.c
+++ b/module01/ex03/main.c
@@ -1,4 +1,5 @@
 #include <avr/io.h>
+#include <util/delay.h>
 
 // stringify
 #define STRINGIFY_HELPER(x)		#x
@@ -64,11 +65,49 @@
 #define TIME_MS(ms)					(((F_CPU / PRESCALE_VALUE) * ms) / 1000)
 #define PERIOD						1000
 #define DUTY_CYCLE					10
+#define PERCENT(percent, period)	(((float)percent / 100) * period)
 
 // END MACROS
 
+typedef struct {
+    int duty_cycle;
+    int max;
+	int min;
+} IncrementParams;
+
+void increment_duty_cycle(void *param) {
+	IncrementParams *params = (IncrementParams *)param;
+	if(params->duty_cycle < params->max) {
+		params->duty_cycle += 10;
+	}
+	OCR1A = TIME_MS(PERCENT(params->duty_cycle, PERIOD));
+}
+
+void decrement_duty_cycle(void *param) {
+	IncrementParams *params = (IncrementParams *)param;
+	if(params->duty_cycle > params->min) {
+		params->duty_cycle -= 10;
+	}
+	OCR1A = TIME_MS(PERCENT(params->duty_cycle, PERIOD));
+}
+
+void on_press(int bit, void (*action)(void*), void *params) {
+	if ((TEST(PIND, bit)) == 0) {
+	    action(params);
+	    _delay_ms(20);
+	    while ((TEST(PIND, bit)) == 0) {
+	        continue;
+	    }
+	    _delay_ms(20);
+	}
+}
 
 int main() {
+	int duty_cycle = DUTY_CYCLE;
+    int max = 100;
+	int min = 0;
+    IncrementParams params = {duty_cycle, max, min};
+
 	MODE_OUTPUT(LED2);
 
 	// Table 16-4 : set timer in Fast PWM (Pulse With Modulation) mode with TOP = ICR1 (Mode 14)
@@ -83,12 +122,13 @@ int main() {
     ICR1 = TIME_MS(PERIOD);
     
     // 16.9.3 : set the duty cycle to DUTY_CYCLE% of the time -> OC1A (alternate function of PORTB1, aka LED2) is cleared when TCNT1 (the counter value) equals OCR1A
-    OCR1A = TIME_MS(DUTY_CYCLE);
+    OCR1A = TIME_MS(PERCENT(DUTY_CYCLE, PERIOD));
 
     // start the timer with the prescaler
     TCCR1B |= (PRESCALE_SET);
 
 	while(1) {
-		continue;
+		on_press(SW1, increment_duty_cycle, &params);
+		on_press(SW2, decrement_duty_cycle, &params);
 	}
 }
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