diff --git a/GpsTracker/GpsTracker.ino b/GpsTracker/GpsTracker.ino
index 58b26dc..9647e3e 100644
--- a/GpsTracker/GpsTracker.ino
+++ b/GpsTracker/GpsTracker.ino
@@ -32,5 +32,5 @@ void loop() {
 		positions::send();
 	}
 
-	mainunit::deepSleep(10); //duration TBD
+	mainunit::deepSleep(10); //TODO : duration
 }
diff --git a/GpsTracker/Hardware.cpp b/GpsTracker/Hardware.cpp
index 11033ae..44e0f56 100644
--- a/GpsTracker/Hardware.cpp
+++ b/GpsTracker/Hardware.cpp
@@ -73,6 +73,8 @@ namespace hardware {
 		uint8_t powered = 0;
 
 		void powerOn() {
+			if (powered > 0) return;
+
 			digitalWrite(I2C_PWR, HIGH);
 			pinMode(I2C_PWR, OUTPUT);
 
diff --git a/GpsTracker/MainUnit.cpp b/GpsTracker/MainUnit.cpp
index f2e1f82..da7e796 100644
--- a/GpsTracker/MainUnit.cpp
+++ b/GpsTracker/MainUnit.cpp
@@ -9,7 +9,9 @@ namespace mainunit {
 	}
 
 	void interruptIn(uint16_t seconds) {
+		rtc::powerOn();
 		rtc::setAlarm(seconds);
+		rtc::powerOff();
 
 		pinMode(RTC_WAKE, INPUT);
 		attachInterrupt(digitalPinToInterrupt(RTC_WAKE), interrupt, FALLING);
diff --git a/GpsTracker/Time2.cpp b/GpsTracker/Time2.cpp
index 374a805..0bdd1c3 100644
--- a/GpsTracker/Time2.cpp
+++ b/GpsTracker/Time2.cpp
@@ -38,7 +38,7 @@
 static  const uint8_t monthDays[] = { 31,28,31,30,31,30,31,31,30,31,30,31 }; // API starts months from 1, this array starts from 0
 
 __attribute__((__optimize__("O2")))
-void breakTime(timestamp_t timeInput, tmElements_t &tm) {
+void breakTime(const timestamp_t timeInput, tmElements_t &tm) {
 		// break the given timestamp_t into time components
 		// this is a more compact version of the C library localtime function
 		// note that year is offset from 1970 !!!
@@ -95,7 +95,7 @@ void breakTime(timestamp_t timeInput, tmElements_t &tm) {
 }
 
 __attribute__((__optimize__("O2")))
-timestamp_t makeTime(tmElements_t &tm) {
+timestamp_t makeTime(const tmElements_t &tm) {
 	// assemble time elements into timestamp_t 
 	// note year argument is offset from 1970 (see macros in time.h to convert to other formats)
 	// previous version used full four digit year (or digits since 2000),i.e. 2009 was 2009 or 9
diff --git a/GpsTracker/Time2.h b/GpsTracker/Time2.h
index d62535e..3afa0c8 100644
--- a/GpsTracker/Time2.h
+++ b/GpsTracker/Time2.h
@@ -23,5 +23,17 @@
 	} 	tmElements_t, TimeElements, *tmElementsPtr_t;
 
 	/* low level functions to convert to and from system time                     */
-	void breakTime(timestamp_t time, tmElements_t &tm);  // break timestamp_t into elements
-	timestamp_t makeTime(tmElements_t &tm);  // convert time elements into timestamp_t
+	void breakTime(const timestamp_t time, tmElements_t &tm);  // break timestamp_t into elements
+	timestamp_t makeTime(const tmElements_t &tm);  // convert time elements into timestamp_t
+
+	tmElements_t operator += (const timestamp_t b) {
+
+	}
+
+	tmElements_t operator + (const tmElements_t a, const timestamp_t b) {
+		tmElements_t result;
+		timestamp_t aTimestamp = makeTime(a);
+		breakTime(aTimestamp + b, result);
+
+		return result;
+	}