3.3v Pro Mini, Radio, Moisture Sensor and StepUp regulator - AA battery power

  • Hello,

    The current draw from 2 AA batteries (in series) when running this configuration is 2ma when in sleep mode. In my view is way to high. At 2200 mah, I calculate only getting about 45 days of battery life (2200mah / 2ma / 24 hrs/day).

    Are my calculations correct?

    While sleeping, removing the radio does not change the load on the batteries (it remains at 2ma).

    Removing the Power LED on the PRO Mini will only reduce the current draw to about 1ma, giving 90 days of battery life.

    I have tried the gw.sleep mode and my own sleep mode and get the same results.

    Not sure how people are getting current draws below 1ma...


  • Mod

    Yes, your calculations are correct.

    Without the power led the Pro Mini should consume about 0.54mA (source). How accurate is the ammeter you are using?
    Removing the voltage regulator will lower the power consumption an additional 0.5mA, ending up at approximately 45uA.

    What else (besides the radio) is connected to the Pro Mini? How much current does the moisture sensor consume?

    Most cheap step-ups consume quite a lot of power, it could be the step-up that is consuming all that power. Try comparing measurements taken before and after the step-up. You might need to remove the step-up to get good battery life.

  • @y4CdW42Ol8
    How is the moisture sensor fed from? Directly from the stepup regulator?

    I have some sensors that require 5VDC as in input. I power them from a separate DO-line. This makes the sensor consume hardly any power while the pro-mini (euuuuuhm Atmel 326) is asleep. (approx. 17 uA if I'm correct)

    works very well for me.


  • I will try all your suggestions.
    Thanks much.

  • @mfalkvidd

    I hesitate to remove the regulator. I rendered one Pro Mini useless trying to cut the trace to the Power LED.

    I will try removing the StepUP. But not sure what will happen to the Pro Mini when the voltage dropes below 3.3v...

    I was hoping that the Pro Mini will continue to run when the voltage to it drops below 2 volts.

  • Mod

    @y4CdW42Ol8 yes removing the components can be a bit tricky. I killed 3-4 Arduinos before I got the hang of it.

    The Pro Mini will work down to 2.8V with the default BOD settings. If you turn off BOD (see instructions in the link I posted above) it can work down to 2.34V at 8MHz according to specs (and lower if you are lucky). At 1MHz the Pro Mini can work down to 1.9V which is the lower limit for the nrf24l01.

  • @mfalkvidd

    How do you drop the frequency to 1Mhz? Change the crystal? Is there a software way to do that?

    I have since removed the Pro Mini power LED and the current dropped to 102 micro amps (with the moisture sensor removed). With the moisture sensor board IN and its LED removed, the draw is 1.4 ma - not so good (regulator still in).

    I found that I can read the analog voltage (A0) using only the moisture probe (and not the board). It varies from 1.11v (dry) to 1.66v (fully wet) - but then no interrupts. I will try a 12hr wake up timer (as mentioned)...


  • Mod

    You might want to use the method described in my thread about plant monitoring. The sketch is available at github: https://github.com/mfalkvidd/arduino-plantmoisture

    I don't use the moisture board either. Power to the sensor is cut completely off when the Arduino is sleeping. See the end of the thread for battery measurements.

    The frequency can be dropped to 1MHz by changing fuses. No need to change crystal. Settings for fuses can be found here: http://eleccelerator.com/fusecalc/fusecalc.php?chip=atmega328p&LOW=46&HIGH=C6&EXTENDED=07&LOCKBIT=FF
    How to set fuses using another Arduino is described here: https://www.arduino.cc/en/Tutorial/ArduinoISP
    I haven't bothered changing clock though, since my sensors seem to get many years of battery life at 8MHz.

  • Wow, I could never come up this sketch! I get the gist of it, but it will take me some time to figure out exactly how it works. I'm still learning the code syntax.

    I don't understand: MySensor gw; and your other gw library calls like:

    MyMessage msg(CHILD_ID, etc..)
    MyMessage voltage,etc... and
    gw.present(CHILD_ID ...)

    Are these explained somewhere?

    I was not going to use this library, but rather just another Pro Mini to "receive" the data from the sensor, using the RF24.h library. I have that working.

    Can I use the gw library just using another Pro Mini? Do you have the "receive" sketch?


  • Mod

    @y4CdW42Ol8 those calls are to the MySensors library . You are in the MySensors forum 😄
    Starting at https://www.mysensors.org/about/ is the best way to learn about MySensors.

    The receive sketch is called a gateway. Read the links I posted for you in https://forum.mysensors.org/topic/4093/what-does-a-gateway-do/1 to learn about gateways.