#Arduino delay 30 seconds serial#

They're more accurate than the Arduino's ceramic resonator, though. Many GPS modules have the ability to output a 1-second pulse which is synchronised to the GPS clock.Īn RTC module would improve accuracy somewhat as well - again most of those have a 1Hz square wave output that can be used to synchronise things - however, even those aren't 100% accurate and rely on the accuracy of the attached crystal. If you require an exact 1-second pulse with near zero drift you will have to use an external clock source. The problem is, since what you are measuring the drift against is itself drifting, your measurements are completely meaningless. While it may appear to be accurate, in that it would give you round numbers '1000, 2000, 3000, 4000' etc, compare that to an external clock and you would find it's actually drifting just as bad (if not worse) than your existing methods. That is - it triggers on the rollover between 1000 millisecond blocks where 1 millisecond is whatever the Arduino's millis() function thinks 1 millisecond is. However, all that gives you is a precise 'Arduino 1000 millisecond' delay. Would give you a precise 1000 millisecond 'delay'. You can't rely on that giving you a precise time - otherwise, something as simple as: uint32_t secs = 0 You have no reliable time-base to measure time against. Your biggest problem is that you don't know what a second is. OK in test code, don't do this in production code. TIMSK1 = _BV(OCIE1A) // interrupt on output compare A TCCR1B = _BV(WGM12) // CTC mode, TOP = OCR1A TCCR1A = 0 // undo the Arduino's timer configuration Here is a modified version of your program illustrating the points In this case, you would have it repeatedly count from 0 to 62,499 Match) and let it reset itself when it reaches a value of your choosing. Instead, set it to CTC mode (clear timer on compare The right thing to do is to never reset a timer if you want it to have That would certainly reduce the risk, but It has been suggested to you to move this lineīefore the Serial.println(). Interrupt fires but before you have time to execute the line above, then If the timer happens to increment after the Time depends on whether there is already an interrupt handler (or otherĬritical section) running. Dispatching an interrupt takes time, and this Thus, you should think of millis()Īs being good to within ☒ ms. Every now a then it is updated by 2 ms at once in True millisecond resolution: it is a counter that is updated everyġ024 µs. Program like yours, I would advise you against doing it in production However, while it can be OK to do that in a small test To be safe, because at this rate you are never going to fill the outputīuffer anyway. Interrupts, using it with interrupts disabled can lock your program if

#Arduino delay 30 seconds serial#

This should normally avoided: since Serial relies on In other words, you can get something that is really close to a However, get a delay which is pretty close to the CPU's idea of one Typical drift is of the order ofġ,000 ppm, and is affected by temperature and aging.

Majenko is perfectly right: you cannot expect much accuracy from anĪrduino clocked by a ceramic resonator.