I'm starting a project that evolve some kind of multiple small physical IoT objects that can be plugged dynamically to a wood board and trigger some leds. My question is so simple that I'm afraid of posting it :D How I can store, inside each of those small objects, a regular ID as 12345 ?

  • I want to be able to read that dynamically, as the object can be plugged/unplugged on demand on the board.
  • I want those objects to be passive (without battery) with just Non-volatile memory

I run everything with a RaspberryPi and an arduino (ESP8266).

I've looked into EEPROM, NFC tags, etc... In fact, I would like exactly what an NFC tags is able to do but without the antenna and the reader...

Do you have ideas and/or examples of projects that could help me ?

  • I'm not really sure this is actually an IoT question, but anyway... how many different unique ids do you need?
    – hardillb
    Mar 22, 2019 at 19:43
  • might be able to use a color sensor and colored stickers. Or magnets of different strength/polarity and a hall-effect sensor. or perhaps just two contacts with a fixed resistor in there, which you measure via the MCU.
    – dandavis
    Mar 22, 2019 at 21:17
  • Just asking to clarify: would a usb flash stick work? I know they are quite but they don’t need battery and just a usb port Mar 22, 2019 at 22:17
  • what do you mean by plugged dynamically to a wood board? ..... is there electronic circuitry inside the wooden board?
    – jsotola
    Mar 23, 2019 at 2:37
  • 1
    I think this is more of a general electronics problem than IoT. A one-wire flash device might do ( the DS18b20 temp sensor is where I've used this). Mar 26, 2019 at 17:47

1 Answer 1


Given the low number (20) of devices then you might be able to get away with just set of different resistors. If you use more than 1 path then this could be a combination of resistors (e.g. path 1 10 ohms, path 2 100 ohms). This would reduce the number of different resistances you would need while still easily creating ways of representing many more than 20 unique ids.

If that doesn't suite then using something like a i2c eprom to hold the id value. Both Pi's and Arduino's can read from i2c buses and the act of plugging the device in could trigger a rescan of the bus and then read the value from a known bus address.

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