diff --git a/GPXTracker.ino b/GPXTracker.ino
index 2cc71f3..8d5d231 100644
--- a/GPXTracker.ino
+++ b/GPXTracker.ino
@@ -1,13 +1,71 @@
 #include <TinyGPS++.h>
 #include <SoftwareSerial.h>
+#include <SD.h>
 
 #define BUFFER_SIZE 256
 #define SERIAL_TX_PIN 4
 #define SERIAL_RX_PIN 5
 
-TinyGPSPlus gps;
+#define SD_CS_PIN 15
+
+#define MAX_LOOP_RUN 120
+#define LOOP_DELAY_RUN_MS 200
+
+#define LED_PIN 2
+
+#define LED_ERROR_DEALY_MS 100
+#define LED_PROGRESS_DELAY_MS 200
+
+#define MAX_SLEEP_TIME_MS 60 * 1000
+
 SoftwareSerial serialGPS(SERIAL_RX_PIN, SERIAL_TX_PIN); 
 
+void blinkLED(int count, int delayMS) {
+  for (int i = 0; i < count; i++) {
+    digitalWrite(LED_PIN, LOW);
+    delay(delayMS);
+    digitalWrite(LED_PIN, HIGH);
+    delay(delayMS);
+  }  
+}
+
+void errorLED(int count) {
+  blinkLED(count, LED_ERROR_DEALY_MS);
+}
+
+void progressLED(int count) {
+  blinkLED(count, LED_PROGRESS_DELAY_MS);
+}
+
+void okLED() {
+  blinkLED(1, 1000);
+}
+
+void writeTrackPoint(File gpxFile, TinyGPSPlus gps) {
+  float latitude = gps.location.lat();
+  String latitudeStr = String(latitude , 6);
+  float longitude = gps.location.lng();
+  String longitudeStr = String(longitude , 6);
+
+  gpxFile.print("<trkpt lat=\"");
+  gpxFile.print(latitudeStr);
+  gpxFile.print("\" lon=\"");
+  gpxFile.print(longitudeStr);
+  gpxFile.print("\"><time>");
+  gpxFile.print(gps.date.year());
+  gpxFile.print("-");
+  gpxFile.print(gps.date.month());
+  gpxFile.print("-");
+  gpxFile.print(gps.date.day());
+  gpxFile.print("T");
+  gpxFile.print(gps.time.hour());
+  gpxFile.print(":");
+  gpxFile.print(gps.time.minute());
+  gpxFile.print(":");
+  gpxFile.print(gps.time.second());
+  gpxFile.println("Z</time></trkpt>");
+}
+
 void setup() {
   Serial.begin(9600);
   while (!Serial) {
@@ -15,52 +73,60 @@ void setup() {
   }
 
   serialGPS.begin(9600);
-  //serialGPS.begin(115200);
+
+  pinMode(LED_PIN, OUTPUT);
+  digitalWrite(LED_PIN, HIGH);
+
+  if (!SD.begin(SD_CS_PIN)) {
+    Serial.println("SD startup failed");
+    errorLED(10);
+    while(1);
+  }
+
+  Serial.println("Setup finished");
 }
 
 void loop() {
-  //Serial.println("Running loop...");
-  while (serialGPS.available() > 0) {
-    //Serial.println("GPS data available");
-    if (gps.encode(serialGPS.read())) {
-      //Serial.println("GPS data read");
-      if (gps.location.isValid()) {
-        //Serial.println("GPS location valid");
-        float latitude = gps.location.lat();
-        String latitudeStr = String(latitude , 6);
-        float longitude = gps.location.lng();
-        String longitudeStr = String(longitude , 6);
+  Serial.println("Running loop");
+  File gpxFile = SD.open("gpx.txt", FILE_WRITE);
+  if (!gpxFile) {
+    errorLED(15);
+    Serial.println("Unable to open file for writing");
+    return;
+  }
+  
+  TinyGPSPlus gps;
+  int run = 0;
+  bool success = false;
+  while (!success && run < MAX_LOOP_RUN) {
+    while (serialGPS.available() > 0) {
+      if (gps.encode(serialGPS.read())) {
+        if (gps.location.isValid()
+            && gps.date.isValid()
+            && gps.time.isValid()) {
 
-        Serial.print("Lat: ");
-        Serial.print(latitudeStr);
-        Serial.print(" Lon: ");
-        Serial.println(longitudeStr);
-      }
+          success = true;
 
-      if (gps.date.isValid()) {
-        Serial.print("Date: ");
-        Serial.print(gps.date.year());
-        Serial.print("/");
-        Serial.print(gps.date.month());
-        Serial.print("/");
-        Serial.println(gps.date.day());
-      }
-
-      if (gps.time.isValid()) {
-        Serial.print("Time: ");
-        Serial.print(gps.time.hour());
-        Serial.print(":");
-        Serial.print(gps.time.minute());
-        Serial.print(":");
-        Serial.println(gps.time.second());
-      }
-
-      if (gps.location.isValid()
-          && gps.date.isValid()
-          && gps.time.isValid()) {
-        Serial.println("location, date and time are valid");            
+          writeTrackPoint(gpxFile, gps);
+          
+          Serial.println("location, date and time are valid");
+        } else {
+          run++;
+          errorLED(2);
+          delay(LOOP_DELAY_RUN_MS);
+        }
       }
     }
   }
-  delay(500);
+
+  gpxFile.close();
+
+  if (success) {
+    okLED();
+  } else {
+    errorLED(5);
+  }
+
+  Serial.println("Sleeping...");
+  ESP.deepSleep(MAX_SLEEP_TIME_MS * 1000);
 }