[time-nuts] keeping Arduino timekeeping and clock synced up

Jim Lux jimlux at earthlink.net
Sun Jan 19 19:38:31 EST 2014


On 1/19/14 4:10 PM, Tom Van Baak wrote:
>> So, do you run the whole thing off 12V (which is what I'm going to do)
>> and a float charged battery OR do you do something clever like detect
>> when power is failing and save it in NV storage, then when you come back
>> up, you send a bunch of clock ticks real fast to catch up.
>
> Use a high-res Arduino web cam facing the wall of clocks and write OHR (Optical clock-Hand Recognition) code. That way its a single robust solution for setting it the first time, restarting it on power failure, resyncing after replacing a failed clock, or self-correcting after any mechanical glitch. You can also use the same video feed to show off the project live on the JPL web site.
>


No, a low res cam with a robotic arm that moves it in front of each 
clock in turn..

That is what is called "scope creep"..

I'll be happy if I get ONE clock running reasonably..

I've got the Arduino code running that does the EOT, once a second (but 
using delay(1000) not the ISR), calculates the rate estimate, and 
accepts a sync command over the (emulated) serial port to set the time 
and date.

Curse the folks who develop "processing" because the current version 
supports Mac OSX 10.7 and later, but not 10.6, which I am using, so I 
don't have the nifty "click here to sync the Arduino" routine that's 
provided as an example with the Arduino Time library.


Next I have to integrate the code I've got now with the other sketch 
that does the ISR off the hardware timer.


---

#include <Time.h>


// Solar clock to drive mechanical mechanism
// Jim Lux, 19 Jan 2014

#include <math.h>
#define TIME_MSG_LEN  11   // time sync to PC is HEADER followed by Unix 
time_t as ten ASCII digits
#define TIME_HEADER  'T'   // Header tag for serial time sync message
#define TIME_REQUEST  7    // ASCII bell character requests a time sync 
message
// T1262347200  - sample sync message

const double refclk=31376.6;  //16 MHz/510?
const int clkpin1=6;          // pins going to external clock
const int clkpin2= 7;

int dd, hh;      //current day and hour
boolean UpdateClockFlag; // tells loop() that an interrupt has occurred

void setup(){

   pinMode(clkpin1,INPUT);      // set pins as inputs High Z for now.
   pinMode(clkpin2,INPUT);

   Serial.begin(9600);
   delay(1000);
   UpdateClockFlag = false;
}


void loop(){
   int DOY;
   double e1,e2;
   double secsperday,ratedelta;
   time_t t;

    t = now();      // get the time
   if(Serial.available() )
   {
     processSyncMessage();
   }
   delay(1000);                // hack, til we get ISR timer running
   UpdateClockFlag = true;    // hack

   if (UpdateClockFlag) {
     if(timeStatus() == timeNotSet)
       Serial.println("waiting for sync message");
     else  {

       DOY = DayWeekNumber(year(),month(),day(),weekday());
       hh = hour();
       e1 = eot(DOY,hh);        // EOT in minutes
       e2 = eot(DOY,hh+1);
       secsperday = (e2-e1)*1440;
       ratedelta = secsperday*1.E6/86400;     //ppm for now,
                                            // but we'll change to 
divisor later
       Serial.print(ratedelta); Serial.print(" ");
       digitalClockDisplay();
       // code in here to update interrupt divisor, etc.
     };
     UpdateClockFlag = false;
   }
}


// equation of time code from Tom Van Baak
//http://www.leapsecond.com/tools/eot1.c
double eot(int day,int hour){
     double Pi = 4 * atan(1);

         double y = (2 * Pi / 365.0) * (day - 1 + (hour - 12) / 24.0);
         double eqtime = 229.18 *
                 ( 0.000075
                 + 0.001868 * cos(y)
                 - 0.032077 * sin(y)
                 - 0.014615 * cos(2*y)
                 - 0.040849 * sin(2*y)
                 );
         return(eqtime);
}
void processSyncMessage() {
   // if time sync available from serial port, update time and return true
   while(Serial.available() >=  TIME_MSG_LEN ){  // time message 
consists of header & 10 ASCII digits
     char c = Serial.read() ;
     Serial.print(c);
     if( c == TIME_HEADER ) {
       time_t pctime = 0;
       for(int i=0; i < TIME_MSG_LEN -1; i++){
         c = Serial.read();
         if( c >= '0' && c <= '9'){
           pctime = (10 * pctime) + (c - '0') ; // convert digits to a 
number
         }
       }
       setTime(pctime);   // Sync Arduino clock to the time received on 
the serial port
     }
   }
}

void digitalClockDisplay(){
   // digital clock display of the time
   Serial.print(hour());
   printDigits(minute());
   printDigits(second());
   Serial.print(" ");
   Serial.print(day());
   Serial.print(" ");
   Serial.print(month());
   Serial.print(" ");
   Serial.print(year());
   Serial.println();
}
void printDigits(int digits){
   // utility function for digital clock display: prints preceding colon 
and leading 0
   Serial.print(":");
   if(digits < 10)
     Serial.print('0');
   Serial.print(digits);
}

int  DayWeekNumber(unsigned int y, unsigned int m, unsigned int d, 
unsigned int w){
   int days[]={0,31,59,90,120,151,181,212,243,273,304,334};    // Number 
of days at the beginning of the month in a not leap year.
//Start to calculate the number of day
  int DOY;
   if (m==1 || m==2){
     DOY = days[(m-1)]+d;                     //for any type of year, it 
calculate the number of days for January or february
   }                        // Now, try to calculate for the other months
   else if ((y % 4 == 0 && y % 100 != 0) ||  y % 400 == 0){  //those are 
the conditions to have a leap year
     DOY = days[(m-1)]+d+1;     // if leap year, calculate in the same 
way but increasing one day
   }
   else {                                //if not a leap year, calculate 
in the normal way, such as January or February
     DOY = days[(m-1)]+d;
   }
   return DOY;
// Now start to calculate Week number
//  if (w==0){
  //   WN = (DOY-7+10)/7;             //if it is sunday (time library 
returns 0)
  // }
//  else{
//    WN = (DOY-w+10)/7;        // for the other days of week
//  }
}




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