Are my documents safe in the root cellar at ~80% humidity?


luckyresistor has been working on his Data Logger project:

There is a large cellar where I could store unused items and documents, but the catch is the humidity there. It is a root cellar near a small brook and the humidity varies between 75% up to 90%.
Archived material should never be exposed to humidity greater than 65%, therefore I have to isolate all documents in boxes from the air of the cellar. But are this boxes safe? Do they keep the humidity away from the documents – even for years?
To have a look into the box environment, I need a data logger. It would be simple to buy one, but much more fun to build one. So a new project is born: I call it the “Data Logger” project.

More details at luckyresistor’s blog.

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  1. Pretty posh (see the total cost in the linked article, heh) and FRAM for logging memory. Whoa. But then I’m a dinosaur. SPI flash would be cheaper with more capacity…

    1. You are absolutely right. Therefore see my minimal version, which is using the internal EEPROM for logging values. And you can simple replace the FRAM with any other kind of persistent RAM. To further saving some cost, you can replace the power source with a simple battery.

      The choice for FRAM was primarily to save power. Writing to flash memory, like to any SD card, requires quite a high amount of power. To increase the overall run-time of the data-logger, using FRAM is expensive but lowers the power footprint of the device.

      1. Not SD cards, which I agree can be an iffy thing, but SPI flash like AT26DF081A.
        From DS: Max program current is 18mA, max page (256 byte) program time is 5msec.
        Ignore startup time (10msec) power use. Consider 1000mAh of power.
        Then in the worst case with that amount of power, we can write 9.5GB to the AT26DF081A. Typical performance is 6X of that, or almost 60GB. Even if we derate the calculation, it’s more than enough to write the 1MB in the chip.
        Also, AT26DF081A is NOR flash, and in the market most manufacturers for the common 8SOIC NOR flash parts stick to 100K cycle endurance rating.

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