diff --git a/Makefile b/Makefile
index e6096a9..aeb205a 100644
--- a/Makefile
+++ b/Makefile
@@ -75,6 +75,6 @@ restore:
 	avrdude -p $(AVRDUDE_MCU_TYPE) -c $(PROGRAMMER_ID) -b $(BAUD_RATE) -P $(SERIAL_PORT) -U flash:w:$(DUMP_ORI)
 
 clean:
-	rm -f main.hex main.bin $(OBJ)
+	rm -f main.hex main.bin *.o
 
 .PHONY : all clean hex flash restore
\ No newline at end of file
diff --git a/module03/ex03/header.h b/module03/ex03/header.h
index 7a93bd3..e0793f2 100644
--- a/module03/ex03/header.h
+++ b/module03/ex03/header.h
@@ -7,7 +7,6 @@
 
 #include "utils.h"
 #include "bitmanip.h"
-#include "timer.h"
 #include "usart.h"
 #include "interrupt.h"
 
diff --git a/module04/ex00/Makefile b/module04/ex00/Makefile
new file mode 100644
index 0000000..2e40cba
--- /dev/null
+++ b/module04/ex00/Makefile
@@ -0,0 +1 @@
+include ../../Makefile
\ No newline at end of file
diff --git a/module04/ex00/bitmanip.h b/module04/ex00/bitmanip.h
new file mode 100644
index 0000000..bf9c297
--- /dev/null
+++ b/module04/ex00/bitmanip.h
@@ -0,0 +1,59 @@
+#ifndef BITMANIP_H
+#define BITMANIP_H
+
+#include "utils.h"
+
+// Bit operations on registers
+#define SET(register, bit)		(register |= (1 << (bit)))
+#define CLEAR(register, bit)	(register &= ~(1 << (bit)))
+#define TEST(register, bit)		(register & (1 << (bit)))
+#define TOGGLE(register, bit)	(register ^= (1 << (bit)))
+
+// Get arguments from tuple-like definitions
+#define ARG_1(v1, v2)			v1
+#define ARG_2(v1, v2)			v2
+#define GET_PORT(args)			ARG_1 args
+#define GET_BIT(args)			ARG_2 args
+// // version with "LED1 B, D1" without parenthesis
+// #define ARG_1(v1, ...)			v1
+// #define ARG_2(v1, v2, ...)		v2
+// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
+// #define GET_BIT(...)			ARG_2(__VA_ARGS__)
+
+// Actions on elements
+// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
+#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
+
+#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
+#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
+#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
+#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
+#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)
+
+// Bit definitions
+#define D1 0
+#define D2 1
+#define D3 2
+#define D4 4
+#define SW1 2
+#define SW2 4
+#define D5B 3
+#define D5R 5
+#define D5G 6
+
+// Elements (port, bit)
+#define LED1		(B, D1)
+#define LED2		(B, D2)
+#define LED3		(B, D3)
+#define LED4		(B, D4)
+#define BUTTON1		(D, SW1)
+#define BUTTON2		(D, SW2)
+#define RGB5_BLUE	(D, D5B)
+#define RGB5_RED	(D, D5R)
+#define RGB5_GEEN	(D, D5G)
+
+#endif // BITMANIP_H
\ No newline at end of file
diff --git a/module04/ex00/header.h b/module04/ex00/header.h
new file mode 100644
index 0000000..4acb896
--- /dev/null
+++ b/module04/ex00/header.h
@@ -0,0 +1,19 @@
+#ifndef HEADER_H
+#define HEADER_H
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/interrupt.h>
+
+#include "utils.h"
+#include "timer.h"
+#include "bitmanip.h"
+#include "usart.h"
+#include "interrupt.h"
+
+//
+// PROTOTYPES
+//
+// main.c
+
+#endif // HEADER_H
\ No newline at end of file
diff --git a/module04/ex00/interrupt.h b/module04/ex00/interrupt.h
new file mode 100644
index 0000000..9668ef7
--- /dev/null
+++ b/module04/ex00/interrupt.h
@@ -0,0 +1,8 @@
+#ifndef INTERRUPT_H
+#define INTERRUPT_H
+
+// 7.3.1 : SREG – AVR Status Register
+#define ENABLE_GLOBAL_INTERRUPT		(1<<SREG_I)
+#define DISABLE_GLOBAL_INTERRUPT	(0<<SREG_I)
+
+#endif // INTERRUPT_H
\ No newline at end of file
diff --git a/module04/ex00/main.c b/module04/ex00/main.c
new file mode 100644
index 0000000..291c3d0
--- /dev/null
+++ b/module04/ex00/main.c
@@ -0,0 +1,8 @@
+#include "header.h"
+
+
+// led RGB D5 must turns on in a loop of colors using PWM
+int main() {
+    while (1);
+}
+
diff --git a/module03/ex03/timer.h b/module04/ex00/timer.h
similarity index 100%
rename from module03/ex03/timer.h
rename to module04/ex00/timer.h
diff --git a/module04/ex00/usart.h b/module04/ex00/usart.h
new file mode 100644
index 0000000..b930036
--- /dev/null
+++ b/module04/ex00/usart.h
@@ -0,0 +1,31 @@
+#ifndef USART_H
+#define USART_H
+
+#define BAUD_PRESCALER(usart_baudrate)	(DIV_ROUND_CLOSEST(F_CPU, (16 * usart_baudrate)) - 1)
+// Table 20-8 : Mode Selection (USART Mode SELect)
+#define ASYNCHRONOUS					(0<<UMSEL01 | 0<<UMSEL00)
+#define SYNCHRONOUS						(0<<UMSEL01 | 1<<UMSEL00)
+// Table 20-9 : Parity Bit Selection (USART Parity Mode)
+#define PARITY_DISABLED					(0<<UPM01 | 0<<UPM00)
+#define PARITY_EVEN						(1<<UPM01 | 0<<UPM00)
+#define PARITY_ODD						(1<<UPM01 | 1<<UPM00)
+// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
+#define STOP_ONE_BIT					(0<<USBS0)
+#define STOP_TWO_BIT					(1<<USBS0)
+// Table 20-11 : Data Bit Selection (USART Character SiZe)
+#define DATA_FIVE_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
+#define DATA_SIX_BIT					(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
+#define DATA_SEVEN_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
+#define DATA_EIGHT_BIT					(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+#define DATA_NINE_BIT					(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
+// 20.11.3 : USART Control and Status Register B (UCSRnB)
+#define RECEIVER_DISABLED				(0<<RXEN0)
+#define RECEIVER_ENABLED				(1<<RXEN0)
+#define TRANSMITTER_DISABLED			(0<<TXEN0)
+#define TRANSMITTER_ENABLED				(1<<TXEN0)
+#define INTERRUPT_RECEIVER_DISABLED		(0<<RXCIE0)
+#define INTERRUPT_RECEIVER_ENABLED		(1<<RXCIE0)
+#define INTERRUPT_TRANSMITTER_DISABLED	(0<<TXCIE0)
+#define INTERRUPT_TRANSMITTER_ENABLED	(1<<TXCIE0)
+
+#endif // USART_H
\ No newline at end of file
diff --git a/module04/ex00/utils.h b/module04/ex00/utils.h
new file mode 100644
index 0000000..1dfefcb
--- /dev/null
+++ b/module04/ex00/utils.h
@@ -0,0 +1,23 @@
+#ifndef UTILS_H
+#define UTILS_H
+
+// stringify
+#define STRINGIFY_HELPER(x)			#x
+#define STRINGIFY(x)				STRINGIFY_HELPER(x)
+
+// concatenate
+#define CONCAT_HELPER(x, y)			x ## y
+#define CONCAT(x, y)				CONCAT_HELPER(x, y)
+
+// mathematics
+#define PERCENT(percent, total)		(((float)percent / 100) * total)
+#define DIV_ROUND_CLOSEST(n, d)		((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d)))
+
+// text
+#define SWITCH_CASE(ch) (((ch) >= 'A' && (ch) <= 'Z') || ((ch) >= 'a' && (ch) <= 'z') ? ((ch) ^ (1 << 5)) : (ch))
+
+// boolean
+#define TRUE						1
+#define FALSE						0
+
+#endif // UTILS_H
\ No newline at end of file