Which battery measurement to use?

  • Hi,

    I am looking into building a battery powered door sensor and I am not sure how to measure the battery.

    There seem to be two methods, one using two resistors and another one here which doesn't.

    It's less work to not use the two resistors, but I was wondering whether there are drawbacks to this method and whether I should use the one with the two resistors?

    I hope somebody can shed some light on that 🙂


  • Mod

    @kiesel the method without resistor can only be used when powering directly from battery. If you use a booster, ldo or similar to transform the voltage from the battery, the method without resistor won't work.

  • @mfalkvidd

    I am planning on using a booster, so that's very good to know, thanks!

  • @mfalkvidd

    If you don't mind me asking here: Will the booster disturb the rfm69? The page about battery driven sensors only mentions the NRF24l01+. Should I power the rfm69 straight from the battery? Or will the 0,1uF ceramic capacitor be enough? It seems like using the booster on the radio would be smart since the node will run for longer on the same set of batteries, if I am not mistaken.

  • Mod

    @kiesel the rfm radios are less sensitive to power fluctuations, so you might not need a capacitor.

    on the other hand, a booster is never 100% efficient.

    But if you get a "good" booster, the battery life will be more limited by the self-discharge of the battery than by the power usage of the node. Same goes for the non-boosted variant.

  • If you go with 2xAA or 2xAAA rechargeable batteries (2.4V) and an Arduino (ATMega328P) without a booster set the BOD level to 1.8V and run your MCU at 1 Mhz.
    With a Vcc of 2.7V and the MUC running at 8 Mhz I have experienced some problem (reset). See here for more details