I have several I2C RTC/NVRAM combo shields, designed for a custom sensor network.
After finishing the project, I decided to offer a modified version for sale to the general public.
But in the meantime, I have several original boards, which I am willing to part with for cost + postage.
What you get for $20 US …
Real Time Clock (year month day hour minute second), with 48 hour backup capacitor.
32K of High Speed Non Volatile Memory
Two 16 bit counters (3.3 volt inputs, 10 Mhz max pulse rate)
5 volt to 3.3 volt I2C level translator (use it to talk to those 3.3 volt devices with your 5 volt Arduino)
Library with simple functions for date, time, counters and storage, and a high speed option which uses a 4x I2C clock rate.
The storage consists of Ferro-Electric RAM. This memory provides non-volatile storage like EEPROM or FLASH, but unlike them it has virtually unlimited write cycle endurance, and no wait states on writing. This shield with the provided library supports a sustained write rate of 33 Kbytes per second… which is about as fast as an Atmega can transfer data over the I2C bus (in 4x mode).
The shields are also designed to handle up to 3 extra 128K NVRAM chips (RAMTRON FM24V10).
You can populate the pads yourself, if you are comfortable soldering surface mount components.
Or order the shield pre-populated, $14 per chip. A fully loaded shield, with RTC and 416K, will cost $60.
The shield is stackable, but has no reset button, as it was designed to stack under an Ethernet shield.
The counter inputs are brought out to a 3 pin female header (cntr 1, grnd, cntr2).
Likewise the level translator is brought out to a female header (clock, grnd, data).
If you are interested, PM me with any questions you may have.