diff --git a/.vscode/settings.json b/.vscode/settings.json
index 53ad538..cce9b3b 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -8,6 +8,7 @@
     "utils.h": "c",
     "bitmanip.h": "c",
     "rush_header.h": "c",
-    "twi.h": "c"
+    "twi.h": "c",
+    "header.h": "c"
   }
 }
diff --git a/Makefile b/Makefile
index 3054d8b..e6096a9 100644
--- a/Makefile
+++ b/Makefile
@@ -12,6 +12,14 @@ PROGRAMMER_ID = arduino
 # original firmware dump
 DUMP_ORI = ../../ressources/dump_atmega328p_ori.hex
 
+# Find all C source files in the current directory
+SRC = $(wildcard *.c)
+# Generate object file names from source file names
+OBJ = $(SRC:.c=.o)
+
+# Compiler flags
+CFLAGS = -mmcu=$(AVRGCC_MCU_TYPE) -D F_CPU=$(F_CPU) $(INCLUDES) -Os
+
 # Detect OS
 OS := $(shell uname -s)
 
@@ -30,13 +38,19 @@ all: hex flash
 
 hex: $(TARGET).hex
 
+# Compile each .c file to corresponding .o file
+%.o: %.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+# Link all object files to create the binary
 # avr-gcc : compiler for AVR microcontrollers, https://gcc.gnu.org/wiki/avr-gcc#Using_avr-gcc, https://gcc.gnu.org/onlinedocs/gcc/AVR-Options.html
 #	-mmcu : the target microcontrolle (ATmega328P)
 #	-D : defines a preprocessor macro (#define F_CPU <value>)
 #	-o : output filename
-$(TARGET).bin: $(TARGET).c
-	$(CC) -mmcu=$(AVRGCC_MCU_TYPE) -D F_CPU=$(F_CPU) $(INCLUDES) $(TARGET).c -Os -o $(TARGET).bin
+$(TARGET).bin: $(OBJ)
+	$(CC) -mmcu=$(AVRGCC_MCU_TYPE) $(OBJ) -o $(TARGET).bin
 
+# Convert binary to hex for flashing
 # avr-objcopy : man avr-jobcopy, https://linux.die.net/man/1/avr-objcopy
 #	-O : specifies output format, Intel HEX
 #		some formats (list not found in any doc) :
@@ -46,6 +60,7 @@ $(TARGET).bin: $(TARGET).c
 $(TARGET).hex: $(TARGET).bin
 	avr-objcopy -O ihex $(TARGET).bin $(TARGET).hex
 
+# Flash the hex file to the microcontroller
 # avr-dude : AVR Downloader/UploaDEr, upload firmware, https://avrdudes.github.io/avrdude, v6.3 https://download-mirror.savannah.gnu.org/releases/avrdude/avrdude-doc-6.3.pdf
 #	-p : specifies the microcontroller -> m328p
 #	-c : programmer-id
@@ -60,6 +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
+	rm -f main.hex main.bin $(OBJ)
 
 .PHONY : all clean hex flash restore
\ No newline at end of file
diff --git a/module03/ex03/colors.c b/module03/ex03/colors.c
new file mode 100644
index 0000000..c801d47
--- /dev/null
+++ b/module03/ex03/colors.c
@@ -0,0 +1,77 @@
+#include "header.h"
+
+
+// Table 14-9 : Port D Pins Alternate Functions
+// OC2B (PD3) : Red
+// OC0B (PD5) : Green
+// OC0A (PD6) : Blue
+void init_rgb() {
+	MODE_OUTPUT(RGB5_RED);
+	MODE_OUTPUT(RGB5_GEEN);
+	MODE_OUTPUT(RGB5_BLUE);
+
+    TCCR0A = 0;											// 15.9.1 : Clear Timer0 control register A
+	TCCR0B = 0;											// 15.9.2 : Clear Timer0 control register B
+	TCCR2A = 0;											// Clear Timer2 control register A
+
+	TCCR0A |= (1 << WGM00) | (1 << WGM01);				// Table 15-8 : Timer0 in Fast PWM mode
+	TCCR2A |= (1 << WGM20) | (1 << WGM21);				// Table 18-8 : Timer2 in Fast PWM mode
+
+    TCCR0A |= (1 << COM0A1);							// Table 15-3 : BLUE - Timer0 Non-inverting mode for Blue (OC0A -> PD6)
+	TCCR0A |= (1 << COM0B1);							// Table 15-6 : GREEN - Timer0 Non-inverting mode for Green (OC0B -> PD5)
+	TCCR2A |= (1 << COM2B1);							// Table 18-6 : RED - Timer2 Non-inverting mode for Red (OC2B -> PD3)
+
+    TCCR0B |= (1 << CS01);								// Table 15-9 : Prescaler 8 → ~8kHz PWM frequency
+    TCCR2B |= (1 << CS21);								// Table 18-9 : Prescaler 8 → ~8kHz PWM frequency
+
+    OCR0A = 0;											// Blue OFF
+    OCR0B = 0;											// Green OFF
+    OCR2B = 0;											// Red OFF
+}
+
+void set_rgb(uint8_t r, uint8_t g, uint8_t b) {
+    OCR2B = r;											// Red (PD3, Timer2 OCR2B)
+    OCR0B = g;											// Green (PD5, Timer0 OCR0B)
+    OCR0A = b;											// Blue (PD6, Timer0 OCR0A)
+}
+
+// convert hex to int : https://stackoverflow.com/a/39052987
+uint8_t hex_to_int(char c) {
+	if (c >= '0' && c <= '9') {
+		return c - '0';
+	}
+	if (c >= 'A' && c <= 'F') {
+		return c - 'A' + 10;
+	}
+	if (c >= 'a' && c <= 'f') {
+		return c - 'a' + 10;
+	}
+	return 0;
+}
+
+// "<< 4" is equivalent to "* 16"
+uint8_t get_red(char *input) {
+	if (input[0] != '#') {
+		return 0;
+	}
+	return (hex_to_int(input[1]) << 4) + hex_to_int(input[2]);
+}
+uint8_t get_green(char *input) {
+	if (input[0] != '#') {
+		return 0;
+	}
+	return (hex_to_int(input[3]) << 4) + hex_to_int(input[4]);
+}
+uint8_t get_blue(char *input) {
+	if (input[0] != '#') {
+		return 0;
+	}
+	return (hex_to_int(input[5]) << 4) + hex_to_int(input[6]);
+}
+
+void set_color(char *color_input) {
+	uint8_t r = get_red(color_input);
+	uint8_t g = get_green(color_input);
+	uint8_t b = get_blue(color_input);
+	set_rgb(r, g, b);
+}
diff --git a/module03/ex03/header.h b/module03/ex03/header.h
new file mode 100644
index 0000000..7a93bd3
--- /dev/null
+++ b/module03/ex03/header.h
@@ -0,0 +1,39 @@
+#ifndef HEADER_H
+#define HEADER_H
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/interrupt.h>
+
+#include "utils.h"
+#include "bitmanip.h"
+#include "timer.h"
+#include "usart.h"
+#include "interrupt.h"
+
+//
+// PROTOTYPES
+//
+// main.c
+// colors.c
+void init_rgb();
+void set_rgb(uint8_t r, uint8_t g, uint8_t b);
+uint8_t get_red(char *input);
+uint8_t get_green(char *input);
+uint8_t get_blue(char *input);
+uint8_t hex_to_int(char c);
+void uart_init();
+void set_color(char *color_input);
+// uart.c
+void uart_init();
+char uart_rx(void);
+void uart_tx(char c);
+// void uart_printstr(const char* str);
+void remove_last_character();
+void fill_str(char input);
+int strlength(volatile char *str);
+void reset_input();
+int is_valid_color_input(char c);
+
+
+#endif // HEADER_H
\ No newline at end of file
diff --git a/module03/ex03/main.c b/module03/ex03/main.c
index cdd82b9..501b7c7 100644
--- a/module03/ex03/main.c
+++ b/module03/ex03/main.c
@@ -1,94 +1,11 @@
-#include <avr/io.h>
-#include <util/delay.h>
-#include <avr/interrupt.h>
+#include "header.h"
 
-#include "utils.h"
-#include "bitmanip.h"
-
-// prototypes
-void init_rgb();
-void set_rgb(uint8_t r, uint8_t g, uint8_t b);
-uint8_t get_red(char *input);
-uint8_t get_green(char *input);
-uint8_t get_blue(char *input);
-uint8_t hex_to_int(char c);
-
-// Table 14-9 : Port D Pins Alternate Functions
-// OC2B (PD3) : Red
-// OC0B (PD5) : Green
-// OC0A (PD6) : Blue
-void init_rgb() {
-	MODE_OUTPUT(RGB5_RED);
-	MODE_OUTPUT(RGB5_GEEN);
-	MODE_OUTPUT(RGB5_BLUE);
-
-    TCCR0A = 0;											// 15.9.1 : Clear Timer0 control register A
-	TCCR0B = 0;											// 15.9.2 : Clear Timer0 control register B
-	TCCR2A = 0;											// Clear Timer2 control register A
-
-	TCCR0A |= (1 << WGM00) | (1 << WGM01);				// Table 15-8 : Timer0 in Fast PWM mode
-	TCCR2A |= (1 << WGM20) | (1 << WGM21);				// Table 18-8 : Timer2 in Fast PWM mode
-
-    TCCR0A |= (1 << COM0A1);							// Table 15-3 : BLUE - Timer0 Non-inverting mode for Blue (OC0A -> PD6)
-	TCCR0A |= (1 << COM0B1);							// Table 15-6 : GREEN - Timer0 Non-inverting mode for Green (OC0B -> PD5)
-	TCCR2A |= (1 << COM2B1);							// Table 18-6 : RED - Timer2 Non-inverting mode for Red (OC2B -> PD3)
-
-    TCCR0B |= (1 << CS01);								// Table 15-9 : Prescaler 8 → ~8kHz PWM frequency
-    TCCR2B |= (1 << CS21);								// Table 18-9 : Prescaler 8 → ~8kHz PWM frequency
-
-    OCR0A = 0;											// Blue OFF
-    OCR0B = 0;											// Green OFF
-    OCR2B = 0;											// Red OFF
-}
-
-void set_rgb(uint8_t r, uint8_t g, uint8_t b) {
-    OCR2B = r;											// Red (PD3, Timer2 OCR2B)
-    OCR0B = g;											// Green (PD5, Timer0 OCR0B)
-    OCR0A = b;											// Blue (PD6, Timer0 OCR0A)
-}
-
-// convert hex to int : https://stackoverflow.com/a/39052987
-uint8_t hex_to_int(char c) {
-	if (c >= '0' && c <= '9') {
-		return c - '0';
-	}
-	if (c >= 'A' && c <= 'F') {
-		return c - 'A' + 10;
-	}
-	if (c >= 'a' && c <= 'f') {
-		return c - 'a' + 10;
-	}
-	return 0;
-}
-
-// "<< 4" is equivalent to "* 16"
-uint8_t get_red(char *input) {
-	if (input[0] == '#') {
-		return (hex_to_int(input[1]) << 4) + hex_to_int(input[2]);
-	}
-	return 0;
-}
-uint8_t get_green(char *input) {
-	if (input[0] == '#') {
-		return (hex_to_int(input[3]) << 4) + hex_to_int(input[4]);
-	}
-	return 0;
-}
-uint8_t get_blue(char *input) {
-	if (input[0] == '#') {
-		return (hex_to_int(input[5]) << 4) + hex_to_int(input[6]);
-	}
-	return 0;
-}
 
 // led RGB D5 must turns on in a loop of colors using PWM
 int main() {
 	init_rgb();
+	uart_init();
 
-	char *input = "#FFFF00";
-	uint8_t r = get_red(input);
-	uint8_t g = get_green(input);
-	uint8_t b = get_blue(input);
-	set_rgb(r, g, b);
     while (1);
 }
+
diff --git a/module03/ex03/uart.c b/module03/ex03/uart.c
new file mode 100644
index 0000000..d8c563b
--- /dev/null
+++ b/module03/ex03/uart.c
@@ -0,0 +1,121 @@
+#include "header.h"
+
+// MACROS
+// USART
+#define USART_BAUDRATE		115200
+#define INPUT_SIZE			7
+
+// GLOBAL VARIABLES
+volatile char color_input[INPUT_SIZE + 1] = {0};
+volatile int input_index = 0;
+
+//
+// FUNCTIONS
+//
+void uart_init() {
+	UBRR0H = (unsigned char) (BAUD_PRESCALER(USART_BAUDRATE) >> 8);					// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
+	UBRR0L = (unsigned char) BAUD_PRESCALER(USART_BAUDRATE);
+	UCSR0C |= ASYNCHRONOUS | PARITY_DISABLED | STOP_ONE_BIT | DATA_EIGHT_BIT;		// 20.11.4 : set Frame Format
+	UCSR0B |= RECEIVER_ENABLED | TRANSMITTER_ENABLED | INTERRUPT_RECEIVER_ENABLED;	// 20.11.3 : enable Receiver and Transmitter, and interrupt on receiver
+	SREG |= ENABLE_GLOBAL_INTERRUPT;												// 7.3.1 : Status Register, bit 7 : I – Global Interrupt Enable
+}
+
+char uart_rx(void) {
+	while (TEST(UCSR0A, RXC0) == 0);												// 20.11.2 : do nothing until there are unread data in the receive buffer (UDRn), (RXCn flag in UCSRnA register set to 1 when buffer has data)
+	return UDR0;																	// 20.11.1 : get data in buffer, UDRn – USART I/O Data Register (read and write)
+}
+
+void uart_tx(char c) {
+	while (TEST(UCSR0A, UDRE0) == 0);												// 20.11.2 : do nothing until UDRn buffer is empty, (UDREn flag in UCSRnA register set to 1 when buffer empty)
+	UDR0 = (unsigned char) c;														// 20.11.1 : Put data into buffer, UDRn – USART I/O Data Register (read and write)
+}
+
+// void uart_printstr(const char* str) {
+// 	while (*str) {
+// 		uart_tx(*str);
+// 		str++;
+// 	}
+// }
+
+ISR(USART_RX_vect) {																// Table 12-7 : we select the code for USART Receive
+	char received_char = UDR0;														// read received character
+	if (received_char == '\b' || received_char == 127) {							// if backspace is received
+		if (input_index <= 0) {
+			return;
+		}
+		if (input_index >= INPUT_SIZE) {
+			return;
+		}
+		remove_last_character();
+		input_index--;
+		uart_tx('\b');  // Move cursor back
+		uart_tx(' ');   // Erase the character on screen
+		uart_tx('\b');  // Move cursor back again
+	} else if (received_char == '\n' || received_char == '\r') {					// if enter is received
+		if (input_index != INPUT_SIZE) {
+			return;
+		}
+		set_color((char *)color_input);
+		reset_input();
+	} else {																		// any other character
+		if (input_index >= INPUT_SIZE) {
+			return;
+		}
+		if (!is_valid_color_input(received_char)) {
+			return;
+		}
+		fill_str(received_char);
+		uart_tx(received_char);
+		input_index++;
+	}
+}
+
+int is_valid_color_input(char c) {
+	if (input_index == 0) {
+		if (c == '#') {
+			return TRUE;
+		} else {
+			return FALSE;
+		}
+	}
+	if (input_index >= INPUT_SIZE) {
+		return FALSE;
+	}
+	if (c >= '0' && c <= '9') {
+		return TRUE;
+	} else if (c >= 'A' && c <= 'F') {
+		return TRUE;
+	} else if (c >= 'a' && c <= 'f') {
+		return TRUE;
+	}
+	return FALSE;
+}
+
+void fill_str(char input) {
+	if (input_index >= INPUT_SIZE) {
+		return;
+	}
+	color_input[input_index] = input;
+}
+
+void remove_last_character() {
+	color_input[input_index] = 0;
+}
+
+int strlength(volatile char *str) {
+	int length = 0;
+	while (*str) {
+		length++;
+		str++;
+	}
+	return length;
+}
+
+void reset_input() {
+	for(int i = 0; i < INPUT_SIZE; i++) {
+		color_input[i] = 0;
+	}
+	uart_tx('\r');
+	uart_tx('\n');
+	input_index = 0;
+}
\ No newline at end of file