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.

Thanks!

 

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.

 

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

Press gently on sensor- switch triggers.

 

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.

 

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