Okay, I updated the code as follows:
unsigned long currentmillis = 0;
unsigned long previousmillis = 0;
unsigned long interval = 10;
unsigned long elapsedmillis = 0;
byte latchpin = 2; // connect to pin 12 on the 74HC595
byte clockpin = 3; // connect to pin 11 on the 74HC595
byte datapin = 4; // connect to pin 14 on the 74HC595
byte testpin5 = 5;
byte ones_seconds = 0;
byte tens_seconds = 0;
byte ones_minutes = 0;
byte tens_minutes = 0;
byte tenths = 0;
byte hundredths= 0;
int segdisp[10] = {
63,6,91,79,102,109,125,7,127,111 }; //segment references using 74HC595 Shift Registers
//The above numbers light up different segments of a digit
byte time_update = 0;// added new flag
void setup()
{
pinMode(latchpin, OUTPUT);
pinMode(clockpin, OUTPUT);
pinMode(datapin, OUTPUT);
pinMode(testpin5, OUTPUT);
Serial.begin(57600);
}
void loop()
{
currentmillis = millis(); // read the time.
elapsedmillis = currentmillis - previousmillis;
if (elapsedmillis >= interval) // 10 milliseconds have gone by
{
previousmillis = previousmillis + elapsedmillis; // save the time for the next comparison
time_update = 1;
// if (elapsedmillis>10){ // commented this out to display time below
// Serial.println (ones_seconds,DEC);
// Serial.println (elapsedmillis,DEC);
// }
// digitalWrite (testpin5, LOW); // used to see how long the nex section took
}
// else {digitalWrite (testpin5, HIGH);} // set flag to upate & shift out
if (time_update == 1){ // no updating if not at 10ms interval, skip this whole section
// increment the counters, roll as needed, shift the digits out
time_update = 0; // reset for next pass thru
hundredths = hundredths +1;
if (hundredths == 10){
hundredths = 0;
tenths = tenths +1;
}
if (tenths == 10){
tenths = 0;
ones_seconds = ones_seconds +1;
Serial.print ( tens_minutes,DEC); // sending minutes/seconds to the screen
Serial.print (ones_minutes,DEC);
Serial.print (tens_seconds,DEC);
Serial.println(ones_seconds,DEC);
}
if (ones_seconds == 10){
ones_seconds = 0;
tens_seconds = tens_seconds +1;
}
if (tens_seconds == 6){
tens_seconds = 0;
ones_minutes = ones_minutes +1;
}
if (ones_minutes == 10){
ones_minutes = 0;
tens_minutes = tens_minutes +1;
}
if (tens_minutes == 6){
tens_minutes = 0;
}
// digitalWrite (testpin5, HIGH); // used to see how long the if's were taking
// counters are all updated now, just do the shiftout one time here:
digitalWrite(latchpin, LOW); // send the digits down to the shift registers!
shiftOut(datapin, clockpin, MSBFIRST, segdisp[hundredths]); // print the % first "hundredths" digit
shiftOut(datapin, clockpin, MSBFIRST, segdisp[tenths]); // print the tens of hundredths digit
shiftOut(datapin, clockpin, MSBFIRST, segdisp[ones_seconds]); // print the % first "seconds" digit
shiftOut(datapin, clockpin, MSBFIRST, segdisp[tens_seconds]); // print the tens of seconds digit
shiftOut(datapin, clockpin, MSBFIRST, segdisp[ones_minutes]); // print the % first "minute" digit
shiftOut(datapin, clockpin, MSBFIRST, segdisp[tens_minutes]); // print the tens of minutes digit
digitalWrite(latchpin, HIGH);
} // end if time to be updated
} // end void loop
am seeing that elapsedmillis = 11 four times a second consistently.
Have it running now, comparing time to my laptop clock, see if they stay in sync together.
Hmm, PC clock not good enough - I get the impression that it drifts a little also, as the two of them don't seem to update once a second together, the display lag between them drifts.