Arduino Real Clock Timer Device - time

Question

hey I have this problem that I have been dealing with for the last few day I have a way around it but I know for a fact that it is really bad way to program and I am really hoping someone can suggest a better way to go about this.
I am trying to get a time from an RTC ( real clock timer) I think that is the acronym anyway ,,,
Its using a DS 1307 IC ,,,,, every time I start and run the program under constant power it boots fine, but the moment I remove the USB cable for around 10 seconds and then reattach it will give me these funny times.
Something like year 2036 and 46 hours and 165 mins really just garbage.
So I read somewhere that these time are just the programs way of saying that there is no connection to the device. That I don't really get because its permanently plugged in but hey thats what it wants.
So here is a basic code that I got from an example that came with the library.
I thought because there is no connection just do a while loop until the device gets connection this works well but it takes like sometimes 10 seconds to boot up.
The RTC has a battery backup connected and with lines SCL to A5 and SDA A4
As I say it work but takes really long to boot up and give me the correct time.
// Date and time functions using a DS1307 RTC connected via I2C and Wire lib
#include <Wire.h>
#include "RTClib.h"
RTC_DS1307 RTC;
void setup () {
Serial.begin(57600);
Wire.begin();
RTC.begin();
Serial.println("RTC capturing time!");
while (! RTC.isrunning())
{
Serial.println("RTC is NOT running!");
Wire.begin();
RTC.begin();
}
Serial.println("RTC IS running!");
// following line sets the RTC to the date & time this sketch was compiled
// RTC.adjust(DateTime(__DATE__, __TIME__));
}
void loop () {
DateTime now = RTC.now();
Serial.print(now.year(), DEC);
Serial.print('/');
Serial.print(now.month(), DEC);
Serial.print('/');
Serial.print(now.day(), DEC);
Serial.print(' ');
Serial.print(now.hour(), DEC);
Serial.print(':');
Serial.print(now.minute(), DEC);
Serial.print(':');
Serial.print(now.second(), DEC);
Serial.println();
Serial.println();
delay(1000);
}
The output looks like this just with A LOT more RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC is NOT running!
RTC IS running!
2013/6/11 22:22:0
2013/6/11 22:22:2
2013/6/11 22:22:3
2013/6/11 22:22:4
2013/6/11 22:22:5
and if I was to not include my while loop idea I get really messed up times and dates as I said before until it for some reason comes right by itself.
Please let me know if anyone knows of a better way to fix my problem I am really confused to why this would be occurring.

Answer 1

Try this code...
void setup () {
Serial.begin(57600);
Wire.begin();
RTC.begin();
Serial.println("RTC capturing time!");
while (!RTC.isrunning())
{
// do not really need this, remove after testing
Serial.println("RTC is NOT running!");
delay(10);
}
Serial.println("RTC IS running!");
// following line sets the RTC to the date & time this sketch was compiled
// RTC.adjust(DateTime(__DATE__, __TIME__));
}

Answer 2

You should clarify how you power the RTC when USB is disconnected. First you should check if the battery is actually good. Then you need to ensure that the Arduino notices that the RTC was battery powered. This is because the RTC will shut down I2C completely while battery powered --> I2C must be reinitialized when power is recovered. The point is that your DS1307 library might not account for that.
In doubt you need to analyze the source code of your library AND read the datasheet of your DS1307 chip.
Another thing is that the datasheet says
the device switches from battery to VCC when VCC is greater than VBAT+0.2V and
recognizes inputs when VCC is greater than 1.25 x VBAT
Did you ever measure VBAT and VCC at startup?