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If an IoT object records data (accelerometer, gyroscope, ...) in memory, what would be the smartest way to retrieve these data after, let's say, 2-3 days?

  • Store in JSON format on an SD Card?
  • Store in Memory then wire: USB?
  • Wireless: with BLE? XBee?

The idea is to retrieve the JSON data very easily from a computer without yet another hub, bridge, etc...

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    \$\begingroup\$ My answer is based on the fact that you are very vague and do not say what your IoT device interacting with the sensors actually has, in terms of capability, existing interfaces, or if you are willing to buy/interface with other modules to do this data retrieving \$\endgroup\$
    – KyranF
    Oct 12, 2014 at 10:32

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If your IoT device can interface with an SD card, then sure, store the data as ASCII bytes, comma seperated, and you can do a very quick import into Micrsoft Excel or any other spreadsheet program. CSV (Comma seperated values) files are very easy to read with a Java program too, perhaps you need a quick custom Java program to convert them to be JSON compatible.

If your IoT device supports USB, you can make it store the data in Flash memory or similar non volatile (or volatile, your choice! if batteries will be good enough for that long) however you must look at the sample rate and data size and expected run time to see if your device actually has enough onboard storage. A very quick custom serial routine can be written to make it dump all the data over serial/USB after request, and you can write a very simple custom C, C++, Java, or C# program to receive and store as a local CSV or JSON format file (whatever you want, really).

If you always have something nearby you can indeed set up an Xbee serial link for remote data storage, or BLE based serial bridge to a nearby "base station" that can do the storage and monitoring.

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  • \$\begingroup\$ Thanks ! The idea is close to Notion or Sen.se cookies that records events. But I don't want to send data on cloud. So the 2 important keys are: size (vs microSD card) and upload of data to a Windows PC (Windows dislike BLE but wireless is a way to handle N objects) I like the sdcard idea because its simple \$\endgroup\$ Oct 12, 2014 at 10:49
  • \$\begingroup\$ Yes, SD card is easy to go and retrieve each sensor's recorded data and it can record for a VERY long time. You can then easily put into a laptop or PC's external SD card reader, and with a custom and very small program you can pull the data off and analyse it \$\endgroup\$
    – KyranF
    Oct 12, 2014 at 10:56
  • \$\begingroup\$ Thanks, and I assume devices should write raw data ? It's not a good idea to try to do smart log ? \$\endgroup\$ Oct 12, 2014 at 11:03
  • \$\begingroup\$ For an SD card, you can afford to write in full JSON format strings. If you were trying to do Xbee transmissions or store in Flash memory to read back later, saving as bytes is far better. \$\endgroup\$
    – KyranF
    Oct 12, 2014 at 11:04

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