I could get the unix time, convert it to days, and subtract most of  the days to make say Aug 1 2011 the datum , then I will have more manageable number to play with for many years to come.....

right, I was getting confused by changing it to binary, but I can keep it decimal.

That was the plan originally Bob, but I I was put off by the 10 digit length of the number, but I think I can do it now

OK I have my event logger basically running, but I now have to calculate the number of days since the last event. ( max 99 )

Without using a lookup table for months days and leap years etc, if I can find how to convert the previous event date to unix time, I could simply subtract it from the current unix time to give me elapsed seconds, and divide by 60*60*24

I can get the current unix time with the time.h library with time_t now() , but I cannot see how to give it another date to calculate from?

Any ideas ?

I could go back to my original idea of splitting the unix code for the previous event, into bytes and saving them in the RTC ram, but its a big number ( 10 digits decimal )

Thanks, yes I got it going like that, now I am doing my manipulations ( and seem to have reset everything to 0 but it doesnt matter, its actually coming right at last !

Code:

#include "Wire.h"
#define DS1307_I2C_ADDRESS 0x68
byte    date_month;
byte    month ;
byte    year;
byte prevdate ;
byte prevmonth ;
byte prevyear ;
byte prevbest ;

int trigger = 7;

void setup () {
 
   Wire.begin(); // no address, we are master
  Serial.begin (9600);  
pinMode ( trigger, INPUT );
digitalWrite ( trigger, HIGH);   //   sets pin 7 as trigger with pullup

//                                        update real time at bootup Read the day of month, month, year
   // Reset the register pointer  
    Wire.beginTransmission(0x68);  
    Wire.send(0x04);  // to day of the month
    Wire.endTransmission();  

    Wire.requestFrom(0x68,3 );  
 //   seconds = Wire.receive();  
 //   minutes = Wire.receive();  
 //   hours = Wire.receive();  
 //   day_week = Wire.receive();  
    date_month = Wire.receive(); // sends back current month  
    month = Wire.receive();  // and this
    year = Wire.receive();   // and this
  //  sqwe = Wire.receive();

   Serial.print ("bootup date_month " );
    Serial.println (date_month, HEX);
       Serial.print ("bootup month " );
    Serial.println (month, HEX);
       Serial.print ("bootup year " );
    Serial.println (year, HEX);

}

void loop () {
// ****************************************

if ( trigger == LOW ) { checkdate () ;}

// **********************************************************************
// Read the first 4 bytes of RAM
    // Reset the register pointer  
    Wire.beginTransmission(0x68);  
    Wire.send(0x08);  // to start of RAM
    Wire.endTransmission();  

    Wire.requestFrom(0x68,4 );  // Read back first four RAM addresses
  prevdate = Wire.receive(); // or whatever you decide to the data
  prevmonth = Wire.receive();
  prevyear= Wire.receive();
  prevbest = Wire.receive();  

 Serial.print ("prev date " );
    Serial.println (prevdate, HEX);
       Serial.print ("prev month " );
    Serial.println (prevmonth, HEX);
       Serial.print ("prev year year " );
    Serial.println (prevyear, HEX);

 Serial.print ("prev best " );
    Serial.println (prevbest, HEX);
// ****************************************************************************
 // Write the first 4 bytes of RAM
   // Reset the register pointer  
    Wire.beginTransmission(0x68);  
    Wire.send(0x08);  // to start of RAM
    Wire.send (prevdate); // or whatver you decide to call the data
    Wire.send (prevmonth);
    Wire.send (prevyear);
    Wire.send (prevbest);
    Wire.endTransmission();
    
} // end loop

void checkdate () {
  
  // Read the day of month, month, year
   // Reset the register pointer  
    Wire.beginTransmission(0x68);  
    Wire.send(0x04);  // to day of the month
    Wire.endTransmission();  

    Wire.requestFrom(0x68,3 );  
 
    date_month = Wire.receive(); // sends back current month  
    month = Wire.receive();  // and this
    year = Wire.receive();   // and this
 

   Serial.print ("todays date_month " );
    Serial.println (date_month, HEX);
       Serial.print ("todays month " );
    Serial.println (month, HEX);
       Serial.print ("todays year " );
    Serial.println (year, HEX);
}  // end checkdate function

Thanks Bob,  I can actually understand most of that !!!

I will be using it in a stand alone board, so the keyboard shortcuts were getting me confused.

Which parts go before set-up and which in loop ?

I am getting really confused ,  all I need to do is use the days, months and years from the RTC date  = " currdate"  and 4 bytes of data from the ram ( 07H - 0AH ) ?  of the DS1307.

I think I can do all the manipulation, but then I want to occasionally write the updated data to the 4 bytes,  without disturbing the preset time .

I cant believe how  I am struggling with this  !  Anybody got a working simple sketch that I can modify?

Right,  slept on it and decided to run it slower ( I have a somewhat suspect usb connection sometimes ) so I changed it to 9600 and it works !

Now I shall try modifying it for my project  Thanks again !

I have 2 Arduinos, one runs on port13 and the other on 27, which is handy when I have them both on for wireless/data links.

I have drawn out ( my printer died yesterday ) the memory map of the 1307, and the addresses for each byte say 00H  to 07H, so I was wondering where the F and E and C  come from?

Yes the symbols appear in short bursts every 5 seconds.

Its definitely something my end :-)  I am going groggy with all this, and have had about 8 hours sleep since Wednesday, so I think I might do some assembly and give my mind a break !  I have 3 projects on the go at once suddenly !

I am still getting oã1š.}¢bzŽÿlc1š.}¢bzŽÿlc1dÞ~¢c{Žÿ  when I switch on.

I set my port 27 that I am using to 57600.

Where does the F0xx   E0xx C0xx  come from ?

That looks great, don't now how you are going to get time for fencing now your a moderator !

I will try that sketch out when I have had my morning coffee.

The extra byte I need to save is historically the best number of days between events, which could have been 5 events ago, but its simply compared to the latest one at an event time, and the largest is then stored as the best.

BTW Rob,  The Bobuino with bells, whistles, inter-cooler and turbo looks really cool !

I don't like to just cut'n'paste without trying to understand the code, I have put some comments on your code to see if I understand it :-

Code:

// Reset the register pointer                          //  because the DS1307 sequences through all the addresses ?
    Wire.beginTransmission(RTC_address);         // this would be 0x68 , the address for all DS1307s ?
    Wire.send(0x00);                                        // starts the sequence back at 00 ( seconds and CH ) ?
    Wire.endTransmission();

// Now read the current time registers
    Wire.requestFrom(RTC_address,8 );    //  imports current time and control in bcd format, sequencing through as above ?
    seconds = Wire.receive();                 //  extract 1 byte from above, 1 nibble tens seconds, one units seconds  ?
    minutes = Wire.receive();                 // and so on
    hours = Wire.receive(); 
    day_week = Wire.receive(); 
    date_month = Wire.receive(); 
    month = Wire.receive(); 
    year = Wire.receive(); 
    sqwe = Wire.receive();

// Reset the register pointer                   
    Wire.beginTransmission(RTC_address); 
    Wire.send(0x08);  // RAM 0x08-0x3F      // advance the pointer to the start of the eeprom or battery ram ?
    Wire.endTransmission();

// Write it to RAM 
    Wire.beginTransmission(RTC_address,8);  //   I dont need time,  but need to save previous best ( 0-99 )
    Wire.send(seconds); 
    Wire.send(minutes);   
    Wire.send(hours);   
    Wire.send(day_week);   
    Wire.send(date_month);   
    Wire.send(month);   
    Wire.send(year);   
    Wire.send(sqwe);
    Wire.endTransmission();

Thanks Rob

What must I change ( apart from the Serial ) to get the main part working with the normal usb?

Just remove the HEX from all the Serialprints ?

I get      ÿ?ñn¢³30 ¿<ðn¢³30 ¿>ðo£322¡ÿ>ñn£°23aß?ño£°23áÿ?ñ  at the moment on the monitor

Thanks Rob

I will have a look at that now

Thanks Rob,  I wondered about that, is that the RC register they talk about in the datasheet?

I can store the previous best number ( 0-99) preferably in 2 bytes ( so I can just use each one - tens and units - easily for the display.)  Although I still have to compare it to  the current elapsed days to see which is the "best"

The date can be yyyy mm dd  or seconds since 1970 .  so I don't know the best way to try to store it.

If I store it in seconds since 1/1/1970 I can easily divide down the difference between latest and stored seconds to get elapsed days, but I still will need to display the previous date after a power down.....?