I am building a timing system for amateur racing. The idea is to have two arduinos some distance apart communicating wirelessly (one at the start, one at the finish).
For timing to be accurate, the arduinos must be in sync. Desired accuracy is 5ms.
if the race is to last 6 hours, (21,600,000 milliseconds) then desired precision would be 0.25ppm (a lot!)
Lets say the system could be re-calibrated every 2 hours - then the minimum precision should be 0.75ppm (still very precise!)
I have initially planned on using Real Time Clocks. I have never worked with one, but it seems they dont provide milliseconds - no good.
Then I came across this. Using an accurate PWM to make a clock:
I ran the test with two arduino NANOs and I have lost 1.27seconds in 1 hour
Although the drift was relativery precise and after correction it was reduced to 28ms - but still too much in just 1 hour.
There are similar systems - but how do they stay in sync?!:
Wireless drag timing system
Any ideas what approach I could take to sync the arduinos accurately?