I don't know, I can't count that high.
3 years, good gravy. What are you counting and what kind of production line has survived 3 years without counting?
There are so many counting devices out there that are reliable that this eeprom business is an unnecessary limitation. Think about those pedometers. Lasts forever, counts high, tracks time, etc.
Explain why you want to power down at all, also. Just curious.
INTP 3 years is a long time. The machine is not built yet. I'm just now finishing up designing and manufacturing the parts. It's somewhat complex with several servos, steppers, and even a small robotic arm to help unload finished parts. I'm starting the assembly soon. I have another custom machine that has a mechanical counter on it. I wanted to take this new machine to the next level with a digital counter on an LCD and keep track of the overall total parts made, not just what was done in a day. As far as the powering down, this machine will be in the garage and not used everyday. Some of guys brought up an issue i did not think about and that is power failure if the machine is powered up. dave-in-nj talked about a battery backup that would supply power long enough to save the count. Lots of things to think over. Thanks all the great ideas.
jndipworm:
I have another custom machine that has a mechanical counter on it. I wanted to take this new machine to the next level with a digital counter on an LCD and keep track of the overall total parts made, not just what was done in a day.
Why not a mechanical counter?
sniff!
What am I, Chopped Liver? (sorry dave)
In post #5, I suggested using a cap as part of the voltage sensing circuit...
Why add a battery? It needs to be maintained.
I think a mechanical display would be nearly bombproof. You can still use optical/digital/fancy methods to count, just use that input and an Arduino to actuate a mechanical counter display.
revised :
While I agree 100% that a mechanical counter would be the most straightforward and easiest to implement, and the last thing to fail....
If you used a power failure circuit like Mr. 'Chopped-Liver' offered using a Super capacitor and it just went on to power the micro, and the power fail part of the sketch wrote to the eeprom for that day, you would have a record of the last count when power was lost.
if you data-log, you will be able to know how many parts you made per day.
with an electronic counter you can see trending of how fast parts are being made and what happens at certain times a day.
it would show when you are more efficient and when your machines are breaking down
and how many hours (parts) you lost due to a failure, things like that.
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unintelegable speech to text below
I agree I'm a cannibal counter[ mechanical counter ] would be the most straightforward easiest in flovent [ implement ] and Lasting [ last thing ]to fail however if you day the log [ datalog] you'll be able to know how many parts you need per day with electronic counter you can see trending of how fast part 2 being made what happens certain times a day when you're more efficient when your machines breaking down how many hours you lost things like that
Text from speech on my cell phone on my ride home sorry for any spelling mistakes
I made fewer mistakes the other 79000 hours today
dave-in-nj:
I agree I'm a cannibal counter[ mechanical counter ] would be the most straightforward easiest in flovent [ implement ] and Lasting [ last thing ]to fail however if you day the log [ datalog] you'll be able to know how many parts you need per day with electronic counter you can see trending of how fast part 2 being made what happens certain times a day when you're more efficient when your machines breaking down how many hours you lost things like thatText from speech on my cell phone on my ride home sorry for any spelling mistakes
I made fewer mistakes the other 79000 hours today
Even with the corrections you made, much of what you wrote dictated is still unintelligible.
That text to speech. Must be the reason you've got nearly twice my posts and less karma 
If datalogging is of any interest to this project, you would do well to put it into an online database. Your power may go out, but server farms (where the cloud lives) is a few orders of magnitude more reliable and redundanter than your garage and Arduino EEPROM
ok, this has reached the peak of silliness!
I agree totally with the mechanical counter being reliable and not subject to power failures or needing to be saved when the machine is shutoff. I was just trying to get fancy. After reading all the post I decided to go with the mechanical counter after all. It is the easiest route. Thanks everyone of your input.
If you're going to use an Arduino to interface an electronic sensor system to count, you can still tack on an LCD display real easily so you can have both. The mechanical will just be there as a safeguard.