Trying to lower power consumption on R-503 fingerprint scanner

I’m working on a fingerprint safe. I’m using a moteino-usb and an R-503 scanner. I haven’t hooked up any lock mechanism yet as I’m not sure what I’ll go with.

My current code puts the moteino to sleep (consuming less than 1ma, lowest I can measure) and uses the WAKE wire on the R-503 as an interrupt. The wire is LOW when a finger is touching the sensor.

The problem lies with the standby power of the scanner. While the moteino is asleep, the scanner is still trying to read prints, consuming about 16ma (rated 20ma in the manual).

Is there a way to either stop the scanner from looking for prints or to efficiently cut power to it altogether?

Was thinking about just using 2 fets or 2 relays. One to power the scanner once the moteino wakes back up, and the other for the lock. Ideally I could just tell the scanner to stop scanning but I have been unsuccessful so far.

Thanks for any ideas!

You left out a very important part. What will wake up your scanner if you manage to put it to sleep or turn it's power off? Isn't that scanner what makes the rest of your system wake up? If it is asleep, there is NO wake up call!

Links to the hardware please.

Scanner manual

The Moteino works very similarly to an Uno (select uno in ide) only with a focus on low power consumption.

There is a separate power supply for the touch sensor, which is rated 2ua. Essentially an entirely separate system acting like a button. (My bad. Left that out of original.)

In the case of actually removing power I could remove the scanner power supply (pin1 in the manual) leaving the power for the touch sensor (pin 6).

Ideally I wouldn’t need a separate relay for this although I suppose it would work. It seems to me there should be a way to tell the scanner to just stop scanning until further notice. Just a command to stop taking pictures.

Thanks for the help

reconsidering... It might not be such a bad idea to directly wire the touch sensor to the relay. The Arduino and sensor would turn off when the finger is lifted but that only means you'd have to keep the finger there until the safe is unlocked. Of course, this means I pretty much limit myself to a solenoid for a lock.

A power supply rated at 2 microamperes? Please explain. I've never seen one of those before. Please post a wiring diagram or schematic.

Here is the scanner manual as linked earlier.

Sorry for lack of clarity. When I say power supply I refer to the seperate power supply pin on the scanner, supplying power to the touch sensor part of the scanner which consumes 2ua. (not an actual power supply) Meanig I can remove the power for the actual scanner and be left with only the touch sensor powered.

Bit difficult to explain. Take a look at the pinout of the scanner.

Any suggestions for an extremely low power switch (mosfet or relay I guess) that will draw very little power when at rest and switch on on a LOW input? Don’t really care about consumption when switched on as it won’t be for long and not very often.

Well that makes some sense. It must be easier to detect a presence or absence of object than to complete a scan. From the scanner manual, I get the feeling that power management might be automatic. Have you measured the actual current that is being passed?

Well lowest I can measure is 1ma so I’m just trusting it on the 2ua. When everything is powered (all 6 pins plugged in) the scanner pulls about 16ma with no finger. It pulls 22 when scanning and 27 with leds on. When I unplug the scanner power I get 0 which means its less than 1ma.

Now I’m interested in powering the touch sensor directly from battery and somehow having the sensor directly wired to a mosfet to power everything else. Not sure how to accomplish this though. It must switch on when LOW and off when HIGH. Could do this with a relay but that pulls power when off.

So.... I think... I could use a P-type mosfet (switching the about +6v from the battery). If i could find one that will drive off at the about 3.9v the touch sensor puts out when not being touched. that mosfet could them power the arduino, scanner, and relay board, triggered on by the low when the sensor is touched.

But, how long did you wait? If it goes into a power down state automatically, it might take a few seconds or minutes to do that.

It's a very long manual, I read as long as I could without it being my project. I suggest looking there again, front to back. People here don't have time for that, though...

I often use this thought, "what do other users do? I can't be alone". A real commercial scanner wouldn't offer a low power mode unless there is some sane way to use it (i.e. without MOSFET switching etc.) in fact, it's likely to have internal MOSFET switching if it has a power down mode.