Use a null terminator instead of $ to mark eeprom end

firmware/firmware.ino

@@ -50,7 +50,7 @@ typedef struct __attribute__((packed)) cardData {
 #define LED_ERROR_BLINK_TIME 50
 
 #define EEPROM_SIZE 4095
-#define EEPROM_END_MARKER '$'
+#define EEPROM_END_MARKER '\0'
 
 enum wifiStates
 {