Standalone Biometric Idle Power Consumption

Discussion in 'The Projects Forum' started by OWVCMark, Jul 14, 2016.

  1. OWVCMark

    Thread Starter New Member

    Jul 14, 2016
    Hey, guys! I've lurked this forum for some time, but I've finally come across an issue I haven't been able to find a definitive answer for.

    I'm working on a project involving a portable unit that is unlocked via a fingerprint scanner.

    Where I'm running into trouble is powering the entire circuit with a portable power source (AA batteries).

    I've researched commercially available portable biometric locking systems (portable pistol safe, locks for doors in your home), and they mostly seem to take 4 AA batteries. So, these solutions are 6V circuits with very little, if any, standby power draw.

    I've found a fingerprint module which seems to suit my purpose, the R302 fingerprint reader. I can purchase this paired with a specialized K202 board that handles all of the communication with the R302. So, the R302 reads a fingerprint, the K202 board sets an output high. That's exactly what I need.

    My issue is that the K202 board requires 12V. Furthermore, the K202 board seems to have a standby power draw of 130mA. This would drain even an 8-cell AA battery bank (required to reach the 12V) in a very short amount of time.

    So, this leaves me with several questions. How are these commercially available products providing fingerprint access powered by 4 AA batteries? I'm assuming all components are 6V, but the only components I can find are 12V. (R302 reader is 6V, by the way. K202 board is the limiting 12V factor as of now.)

    Also, how are they achieving such a low standby power draw? Again, I'm assuming here, but I imagine you "wake" the system up when the fingerprint reader is touched. But, this isn't something I've seen on the DIY side.

    I guess I've just become really frustrated with trying to find a standalone 6V fingerprint reading system with a very low standby power draw. Are these commercial products just using proprietary circuitry? I went into this hoping that it wouldn't be this difficult to track down and/or DIY.

    I'd appreciate if anyone could point me in the right direction on any of the questions I've raised! Or any advice on the project in general.

  2. crutschow


    Mar 14, 2008
    I don't know how the others do it, but you could have the circuit go into a power-down "sleep" mode after a certain length of inactivity with a low power touch-sensitive "wakeup" circuit connected to (or next to) the finger-print reader to turn the power back on.

    You could efficiently generate 12V from the 6V batteries by using a boost switching regulator.
    Note that the battery current drawn by the regulator will be a little more than double the 12V current.
    OWVCMark likes this.
  3. Sensacell


    Jun 19, 2012
    Mount the sensor on a mechanically compliant mount- with a small 'tactile' switch under it.

    Press gently on sensor- switch triggers.
  4. OWVCMark

    Thread Starter New Member

    Jul 14, 2016
    Thanks for the input, guys!

    I considered boosting the 6V, and I think that a "sleep" function likely is the key.

    However, I don't believe the K202 board has this ability.

    My problem lies in that I want to find a standalone fingerprint reader that will activate an output when the correct fingerprint is read. The K202 is this, but draws a constant 130mA.

    I could of course make my own with an Arduino or something similar, but I'd really like it to be "plug and play", as I may implement this in other things.
  5. OWVCMark

    Thread Starter New Member

    Jul 14, 2016
    Creating my own modules with Arduinos would prove very costly, if and when I decide to scale the project to other uses.