Newbie PCB and battery on RAW Voltage measurement



  • Re: 💬 Easy/Newbie PCB for MySensors
    I am building my first Newbie PCB sensor. I am powering with 9V battery on RAW and let the onboard pro mini regulator supply 5V. I am not using a booster.
    I would like to use the battery measurer voltage divider. I recalculated the resistor values to 5M/680K.
    Looking at the schematic of Newbie PCB I see that when the BAT and REG jumpers are NOT connected and also the REG power input is NOT connected I could use the unused booster pin 1 as input for the Voltage divider.
    I would think when jumpering the RAW pin to the not used pin 1 (Vin) of the booster connection I could measure my RAW battery voltage.
    Just looking for confirmation.
    Thanks


  • Mod

    @peerv you can use the booster pin to read the battery voltage or the proto board area. May I ask why are you going to make a battery powered 5v node? That is going to drain battery quite quickly.


  • Hardware Contributor

    @peerv

    drain battery quite quickly

    and 9V isnt a very good choice as well.

    the problem is that most Arduino boards use a linear regulator to drop that 9V to 5V. If you are drawing a mere 50mA, 0.2W is being burnt in this linear regulator with 0.25W being used by the Arduno itself. This is very inefficient!

    An alkaline 9V PP3 has a capacity of between 500 and 600mAh. This really isn’t very high – a typical alkaline AA battery will be at least 2000mAh. 6 series AA cells will provide the same voltage, but a capacity at least 4 times the size!

    From: https://cybergibbons.com/uncategorized/arduino-misconceptions-6-a-9v-battery-is-a-good-power-source/

    I have tried it myself - will never do it again. And that was with a 3.3v pro mini.

    BAT and REG jumpers are NOT connected

    These jumpers are made for different applications. Using RAW as source you should not bridge/connect any of these. The current will flow from RAW (in) to arduino RAW where it will be converted to 5v. You then need a second voltage regulator for the radio 3.3v.

    I would think when jumpering the RAW pin to the not used pin 1 (Vin)

    This would add a second application and VCC to your pcb. I would take @gohan advice.



  • @gohan I am using the sonar distance sensor to measure water level.
    The measurement is only taking once every minute.
    So the sensor is sleeping most of the time.
    To save power I power the sonar from a digital pin.
    Before going to sleep I switch off the sonar.
    In sleep mode my sensor draws only 200 micro amps!
    Thanks @gohan for the link tip.
    I will see how long the battery last in this application.


  • Mod

    200 uA is not very low, usually you should aim at 10 or less, so there has to be something that is drawing excessive standby current



  • @gohan I managed to get it down to 40 microamp in sleep mode now.
    I also read somewhere to set all unused pins to INPUT.
    I am going to try that too.


  • Hardware Contributor

    @peerv - 40uA is what I aim with a Pro Mini 3.3v, sensor, radio and EasyPCB. Should last you a long time! GOod work.!


 

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