AVR-Chat

> The simplest method I have run into is to use FRAM. The write speed 
of 
> SRAM, the non-volatile nature of EE and an endurance of something 
like 1e9 
> cycles.  Ramtron now makes serial FRAMs in up to 256Kb (thats bits).
> 

I have read a little on the Ramtron chips.  they also have a real 
time clock AND FRAM on a chip so that starts to use less parts as 
well as make it easier to write the data.

It seems that for some EEPROM chips, one needs to write a whole page 
and others, one can address individual bits.  At this point, it seems 
to write a page would be simplier as far as keeping track of 
addresses.

But, your comment about the possibility of putting the variables on a 
Memory card seems like a much easier way.  that would make only one 
connection to the PC, and it would also allow each student to carry 
their own timings.

When looking at chips, the low memory count is the thing that limits 
the total duration of a data logger.  By using a memory card, the 
huge storage allows a 'just read every point all the time' method and 
then one can pick out the data when it is back in the spreadsheet.

I have been looking at a brighness device to log how bright the sun 
is over daylight hours.  This would be a once a minute log.  with 
things like soil moisture changing hourly, it seems like a waste of 
memory to store 10 points each minute for a week or two.

If my math is correct, 10 points per minute is 600 points per hour or 
14,400 per day and 100,800 per week.  If 7 points are hourly, that 
drops to around 30,000 points per week.  If each point is a byte, 
then there would be 800,000 bits or 240,000 bits.   That starts to 
get important with a EEPROM or FRAM chip, but not important with a 
memory card.

This is a good discussion for my level of interest although it is 
somewhat over my head for programming.

Dave