Connect with us

Using this magnetic sensor as a wakeup sensor

Discussion in 'Sensors and Actuators' started by kellogs, Oct 28, 2018.

  1. kellogs

    kellogs

    23
    0
    Jan 7, 2014
    for the rest of the circuit. Here is the sensor's datasheet

    However, looking at the diagram of interest makes me think this is going to drain the batteries quite fast due to that LMV324N comparator and its voltage divider on the positive terminal.

    Is there any way to tweak this design for better battery conservation ?

    Thanks

    HMC_1022_as_wakeup_sensor.png
     
  2. Alec_t

    Alec_t

    2,487
    642
    Jul 7, 2015
    There's no way you can reduce the IC's10mA per bridge current requirement significantly. Can't you use a different IC? It doesn't look suitable as a wake-up sensor, unless you are really forced to sense very low magnetic field strengths.
     
    kellogs likes this.
  3. kellogs

    kellogs

    23
    0
    Jan 7, 2014
    I have overlooked that aspect...

    Yes, I need to sense a couple of uT; there are alternatives but only in minute packages with no leads. Extremely hard to hard to hand solder.

    One thing I do not understand, the 4 resisors of that Wheatstone bridge are 1.1k each. Should the drain not be more around 5 mA at 5 V Vdd ? If you look further down in that table there is another parameter given for I_bridge = 5 mA. The parameter is

    Sensitivity Tempco TA= -40 to 125°C, Vb=5V
    TA= -40 to 125°C, Ibridge=5mA

    Or is it that the resistance varies with drawn current, and at 10 mA it is 100 Ohm ? Which still I can not grasp :|
    Thank you
     
  4. Alec_t

    Alec_t

    2,487
    642
    Jul 7, 2015
    Typically, but only for the 1021/1022. Which IC do you have?
    Probably. Then the 10mA figure would relate to a supply voltage closer to the maximum.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    24,860
    2,571
    Jan 21, 2010
    Depending on the rate of change of the magnetic field, you might turn the sensor on intermittently.

    If you can operate it for 100ms every second, the average current drain will be 10% of what it is now.
     
    kellogs likes this.
  6. kellogs

    kellogs

    23
    0
    Jan 7, 2014
    @Alec_t it is the 1022.

    Good idea @(*steve*) however, thinking more about it I don't think I should be using it anyway since it needs to operate around 10 seconds per minute. But out of curiosity, how would I make it work 100ms / sec ? With some combo of a 555 and a transistor maybe ?
     
  7. Alec_t

    Alec_t

    2,487
    642
    Jul 7, 2015
    I think R19/20 could each be at least 10k without any adverse effect.
    If you use the LMV324S, it has a shut-down feature which would conserve a bit of energy.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    24,860
    2,571
    Jan 21, 2010
    I was thinking a microcontroller. You may have to deal with unusual outputs as the device is powered up or down and while it is powered off.
     
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.