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.

    0_1457722773499_upload-28fac2fe-7b37-46d3-85e9-67e27e07c459

    The objective was to explore how long it can operate with a small i.e. CR1620 (3V, 75mAh, until 2V) battery.
    0_1457722630748_upload-35c9f36d-b595-4192-bc6b-8c34957360b2

    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!
    0_1457723198918_upload-4e7ac4b3-037e-4405-9a61-4e40922d33d9

    Dropping to ~0.5uA for a supply voltage of ~2.2V
    0_1457723546818_upload-ca10f390-906f-4842-aa9b-d48946a3a4dd

    The current during wake is ~13mA during ~4ms. This is for reading two magnetic door contacts and the battery voltage.
    0_1457723897902_upload-17ad5c32-d3a6-4005-b56e-308f75dbad0c

    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
    0_1457727155284_upload-80d3071e-35f8-40fe-98a1-c3780037e562

    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 :
    https://www.dmcinfo.com/Portals/0/Blog Files/High pulse drain impact on CR2032 coin cell battery capacity.pdf
    http://www.ti.com/lit/wp/swra349/swra349.pdf
    http://www.embedded.com/electronics-blogs/break-points/4429960/How-much-energy-can-you-really-get-from-a-coin-cell-
    I use this link for battery calc : http://oregonembedded.com/batterycalc.htm


  • 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.

    0_1457896553845_upload-49f13d13-d4ed-46aa-8576-a47e5f271d2e

    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.

    0_1457897897541_upload-dae13a0d-52ee-46c3-b470-425dd5a225a0
    0_1457898169100_upload-60cbec3f-4bb1-480a-a7a8-d5077d6b3f92

    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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