DT_Elapsed timer, how to compensate for inaccuracy over long periods ?

[Darrel Taylor]

PC clocks are usually horrible time keepers.
I had the same problem a while back, thinking the PC would be accurate.

Syncronize the time on the PC with an NTP server before starting the test, and sync it again at the end of the test.
You'll be amazed how far off the PC's clock is.

Also, is your 20Mhz source a crystal, or a resonator?
Resonators are no good for time keeping.

I've tested the elapsed timer to hold within about 4 seconds a week. (with a good crystal)

[BrianS]

I'll try that. I don't have a manual way to sync the PC's clock to a time server as it is locked out and is updated by a local server. So, I don't know exactly when it's clock is updated to a time server. I try to find a better way to compare the time to.

Thanks,
Bryan

[Charles Linquis]

If you really want accurate timekeeping, you can set up an interrupt on zero-crossings of the AC power line.
Or - If you are brave, I can send you a portion of a program I wrote that contacts NTP time servers (requires a Lantronix XPort or similar) and PBPL.
Or - if you are outdoors, you can get time from a GPS module.

[BrianS]

If you really want accurate timekeeping, you can set up an interrupt on zero-crossings of the AC power line.
Or - If you are brave, I can send you a portion of a program I wrote that contacts NTP time servers (requires a Lantronix XPort or similar) and PBPL.
Or - if you are outdoors, you can get time from a GPS module.

Thanks,
Turns out it was the PC clock was updated by the time server during the period I was monitoring the timer. Found that the timer code/circuit keeps very accurate time for my needs.

Bryan