header file modification now takes into account in makefile

firmware/Makefile

@@ -16,6 +16,8 @@ PROGRAMMER=usbtiny
 FLASHER=avrdude -p $(DEVICE) -c $(PROGRAMMER)
 # source files to compile
 SRC = main.c uart.c ir_nec.c settings.c
+# header files.
+HEADER = $(SRC:.c=.h)
 # object files.
 OBJ = $(SRC:.c=.o)
 # listing files.
@@ -73,7 +75,7 @@ flash:
 program: $(TARGET).hex
 
 # compile
-%.o: %.c
+%.o: %.c %.h
 	$(CC) $(CFLAGS) -I. -mmcu=$(DEVICE) -DF_CPU=$(F_CPU) -c -o $@ $<
 
 # link