F20 Suggestion on time/date clock accuracy

Hi -

Experimenting with my F20, I have observed that the date and time keeping facilities are not especially accurate. I recognize that this is to be expected since the F20 does not include a crystal oscillator and so must rely on an internal oscillator in the F20 chip. Microcontroller internal oscillators are never as accurate as crystal or resonator oscillators.

On my particular F20, I have observed that it tends to run fast by nearly 4 minutes in a 24-hour period.

My suggestion would be to add a feature whereby the Master system could transmit a calibration value into the F20 that would scale the pace of the date and time keeping facility. Then, for any specific F20 the user could perform a timing test to determine the error rate for the F20, calculate an appropriate calibration factor, and transmit it to the F20 with a new command or as an optional parameter of the ā€œSā€ command which sets the current time and date. No doubt, this would still not result in a real time clock as accurate as a crystal-controlled clock but would probably come much closer than the current system.

The only other approach that I can see for establishing fairly accurate time/date stamps for the files stored on the SD card is to set the time/date of the F20 just prior to each file open, file write, and file close operation.

Any thoughts on this or words of wisdom that could help?


You are right as the F20 runs using an internal RC that is not accurate. Adding a feature to calibrate the clock would not be very beneficial as any change in temperature and voltage will effect the clock. If time is critical, adding an actual RTC to the design maybe the answer. We also offer ALFAT, which has a built in RTC.

@ ebjoew - I use a GPS receiver for accurate timing.