[SOLVED] Poor battery life on door sensor

  • I’m running a door sensor on an Arduino Pro Mini 3.3v using a 3.2v 1,800 mAh LiFePo4 battery. I’ve removed the LED and voltage regulator and am using an interrupt driven sketch so that the sensor is asleep most of the time. I added some code to also report battery percentage using the Vcc library which uses the 1.1v internal reference of the MCU.

    Everything works great except that the battery life is Very poor. Each time the sensor is triggered I can see the battery percentage falling until the sensor stops responding after about 10 days, at which time the battery is fully discharged.

    Does anyone have any suggestions as to why the sensor is draining the battery so quickly?

  • Mod

    Welcome to the MySensors community @martinb !

    Do you have a multimeter? If so, use it to measure how much current the node is using when it is in sleep mode.

    A debug log from the node can be useful as well, to verify that the node is actually sleeping.

    If you share your sketch, we could see if there is something strange in it.

  • @martinb If the Node is indeed sleeping, perhaps check the reed circuit for leakage?
    The reeds I've used are fed from the junction of two resistors from Vcc to Int, with the reed closing to ground with a cap across.

  • @mfalkvidd

    The power usage is showing as around 6.5 mA all the time.

    This is the sketch I am using:

    // Enable debug prints to serial monitor
    #define MY_DEBUG 
    // Enable and select radio type attached
    #define MY_RADIO_NRF24
    //#define MY_RADIO_RFM69
    #include <SPI.h>
    #include <MySensors.h>
    #include <Vcc.h>
    #define SKETCH_NAME "Binary Sensor"
    #define SKETCH_MAJOR_VER "1"
    #define SKETCH_MINOR_VER "0"
    #define PRIMARY_CHILD_ID 3
    #define PRIMARY_BUTTON_PIN 3   // Arduino Digital I/O pin for button/reed switch
    const float VccMin   = 2.5;           // Minimum expected Vcc level, in Volts.
    const float VccMax   = 3.5;           // Maximum expected Vcc level, in Volts.
    const float VccCorrection = 1.0/1.0;  // Measured Vcc by multimeter divided by reported Vcc
    Vcc vcc(VccCorrection);
    // Change to V_LIGHT if you use S_LIGHT in presentation below
    void setup()  
      // Setup the buttons
    void presentation() {
      // Send the sketch version information to the gateway and Controller
      // Register binary input sensor to sensor_node (they will be created as child devices)
      // You can use S_DOOR, S_MOTION or S_LIGHT here depending on your usage. 
      // If S_LIGHT is used, remember to update variable type you send in. See "msg" above.
      present(PRIMARY_CHILD_ID, S_DOOR);  
    // Loop will iterate on changes on the BUTTON_PINs
    void loop() 
      uint8_t value;
      static uint8_t sentValue=2;
      // Short delay to allow buttons to properly settle
      value = digitalRead(PRIMARY_BUTTON_PIN);
      if (value != sentValue) {
         // Value has changed from last transmission, send the updated value
         send(msg.set(value==HIGH ? 1 : 0));
         sentValue = value;
      float p = vcc.Read_Perc(VccMin, VccMax);
      // Sleep until something happens with the sensor
      sleep(PRIMARY_BUTTON_PIN - 2, CHANGE, 0);

  • Mod

    @martinb Did you build according to https://www.mysensors.org/build/binary ?
    Is the sensor normally-open, or normally-closed; does the door sensor conduct when the door is closed?

  • @yveaux
    I did follow the build instructions in your link, with the reed switch on D3. When the door is closed, the reed switch is closed (conducting).

  • @zboblamont
    The current draw is the same, whether the door is open or closed.

  • @mfalkvidd
    It looks as if the node is going to sleep OK, as I get this from the nodes debug log:

    7116 MCO:SLP:MS=0,SMS=0,I1=1,M1=1,I2=255,M2=255
    "Sleep node, duration 0 ms, SmartSleep=0, Int1=1, Mode1=1, Int2=255, Mode2=255"

    7122 TSF:TDI:TSL
    "Set transport to sleep"

  • Mod

    @martinb after those lines, there is no debug activity until you open/close the door?

  • @mfalkvidd
    That's correct, no further log activity until the next change in state of the door

  • Mod

    @martinb sorry for asking, but what pin is D3 on a promini?

    Edit: is it the one opposite A2?

  • Mod

    @martinb is the current draw the same if you disconnect the reed switch?

    The sketch looks good btw.

  • @mfalkvidd
    It may be my terminology! It's using digital pin 3 (just marked "3" on the Arduino)

  • @mfalkvidd
    The current draw is the same whether the reed switch is open or closed. There is a momentary increase after a change (which I assume is the radio drawing additional power to transmit?)

  • @mfalkvidd
    Yes, I'm using pin 3 which is opposite A2

  • I'm beginning to wonder if it's the NRF24L01 that's the problem. I found this post which might explain my continuous power draw.

  • @martinb
    I replaced the NRF24L01 and now the power consumption has dramatically reduced. Thanks for all the help, as I’m new to MySensors it helped to eliminate other potential issues.

  • Mod

    @martinb nice work! Thanks for reporting back.

  • @mfalkvidd Interesting discussion!

    I've got the same issue with a lux sensor based upon BH1750; battery life is limited to 7-10 days (3V, 9900mAh)
    I gather that it's not possible to use the interrupt method in this case?

    Do you have any suggestions how I can improve battery life?

  • @martinb Did you replace the NRF24L01 with another NRF24L01? iow was it a bad device?

  • @frankvk
    Yes, I did a straight swap and now, after over a week, the battery level hasn’t dropped at all.

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