EEprom endurance

[markedwards]

I need to totalize approximately 1500 hours equipment operating time before
turning on a service indicator. The equipment does not have battery backup so I initially thought about timing and saving minutes/hours in EEprom but was concerned about wearing out the EEprom (write endurance). The only strategy I could think of was to use 16 to 32 bytes of EEprom to save my minute counter(s). Any suggestions how keep track of which EEprom location to increment? Or is there a another timekeeping method?

[Melanie]

Well, couple of suggestions...

The first is to oversize the PICs PSU and have about a two-second reserve... when it detects Power-OFF, it dumps the relative information to EEPROM in the reserve time. Saves saving to EEPROM every minute.

Another is just to keep track of hours. I made a decision on a piece of equipment that is ON for it's entire life only to save hours. If there's a power-outage, yes I'd lose some minutes, but since the timekeeping was for an elapsed Service Timer, plus or minus a couple of days (or even weeks) at the end of a year or two is neither here or there in the great scheme of things.

Another is to use any of Microchips micropower PICs (even a PIC10F series would do this) with an on-board battery just for storing the timekeeping. Don't want to use a Battery? ...then any handy piece of fruit or vegetable with dissimilar metals would do.

A fourth, (did I say a couple of suggestions?)... is to use an external RTC like a DS1307... it has a few bytes of internal RAM (accessible via I2C bus) which is backed-up from the Battery. Use that to store your elapsed time as it doesn't suffer from the WRITE endurance problem.

A fifth... use external memory that doesn't have the problems of serial EEPROM - eg Ramtron's FRAM...

A sixth... etc etc...

Melanie

[markedwards]

Melanie,

Thanks for your suggestions.

If I save every 5 minutes would take over 9.5 years to reach a million writes, 10 minutes would take over 19 years and is probably a good choice.

Mark