Very narrow and minimal switch node - low power consumption experiment

  • Hero Member

    The minimalistic Very narrow and minimal switch node lends itself for some battery experiments. A how low can you go study with a standard MySensors node.


    The objective was to explore how long it can operate with a small i.e. CR1620 (3V, 75mAh, until 2V) battery.

    The node is attached to a 'reed contact' magnetic sensor.
    0_1457722693924_upload-25b14c9d-2d32-4500-9d3c-9fa1af20a253 This one is connected between arduino pin D2 (connector) and GND.

    The node is programmed with the bootloader as described by @m26872 for the My slim battery node.

    The findings:
    ❗ Summary: minimum of 4 years operation ⭐

    Basic setup.. a uCurrent current to voltage converter. This one is set to 1mV per nA ! (0.001uA) The photo below shows the sleep current at ~3.00V supply voltage (nominal battery voltage (ignore the minus sign on the voltmeter. ;-))). Supply current during sleep ~0.9 uA!

    Dropping to ~0.5uA for a supply voltage of ~2.2V

    The current during wake is ~13mA during ~4ms. This is for reading two magnetic door contacts and the battery voltage.

    A simple and conservative calculation (using the Android Electrodroid battery calculator):
    Sleep: < 1uA
    Wake: 13mA during 4ms and awake once every hour
    Average consumption: 1.014uA,
    Battery: 75mAh
    ---> expected lifetime: ~74000 hours = ~8.4 years !
    For a wake-up around every minute this would still be over 4.5 years.

    A CR1620 (dimension 16mm x 2.0mm) with a (75 mAh) capacity would fit perfectly with the Very narrow node in a 16x16mm housing. I am off to build some MySensors keyfobs (remote controls) 😉

  • Admin

    Cool! What the self discharge of the CR1620s?

  • Hero Member

    @hek for an A quality Energizer type: 1%/ year

    these will probable be different but at Euro 0.16 a piece ....

  • Hardware Contributor

    @AWI : nice report 😉

    imho I am not sure it could last so long time (4.5years with a 75mah !). Unfortunately, because of the rated capacity vs effective capacity, coincell brand/vendor, ...
    or maybe for a very basic keyfob..I know it's an estimation lol 🙂
    for a keyfob (depends on application type), we would need signing which would take more than 4ms for the process (and coincell don't like pulse drain > 5mA). But for simple application/sleep mode, I have reported same as you for coincell. And I had not the same sleep current for coincell vs aa/aaa
    If you are interested in coincell resources, maybe you already know it ;), always good to know : Files/High pulse drain impact on CR2032 coin cell battery capacity.pdf
    I use this link for battery calc :

  • Hero Member

    -- revisited ---

    I changed the bootloader to a 8mHz version. As the processor runs 8 times as fast the active period pulse width is now < 0.5 ms (earlier 3.8 ms) The sleep and active consumption have not changed. This would reduce the 'pulse' burden on the coin cell as attentively mentioned by @scalz.


    Something comparable to 'internal resistance' increases as the charge reduces. This will impact the available voltage for the node. I used a conservative figure for battery capacity (50mAh) and a load current of 0.8uA which will be less if battery voltage goes down.


    Have three nodes ready for real life test with constant battery measurement. I hope to report just within five years from now 💤

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