Hello,
I am using the common optical fingerprint sensor. I'd like to depower the device when waiting so that I can run it on batteries. The problem I have is that after the first time it is used the green led stays lit and the current draw is fairly strong.
I'm hoping there is some standby low power node for this that one could use software to enter and leave. But a look at the Adafruit libraries as well as scanning the available manuals doesn't indicate a command for this.
Does anyone know how to get these to go to into some low power state and then wake them as needed?
I am on the verge of creating an ugly solution of using a transistor to shut off the Vcc to it to get it to go to low power mode. (even this is problematic because the it can draw current from Tx/Rx and seems to keep the LED lit when Vcc is unplugged). I'm also not quite sure the best ways to do this from a 3.3v arduino since one would have a 0.7 transistor base drop in an emitter follower configuration, but with a 5v arduino this might be fine.
However, I still think a software solution might be possible because of the following observation. When I start the device from the off position, the arduino can send certain commands to the device such as verifyPassword() and the green LED remians off. It's not until one tries to sense the first fingerprint does the Green LED light up. Thus clearly the LED does not need to be lit just because the device is powered on. Therefore I speculate there must be someway to send a reset that would put the device back into this iniital power-on state where the LED is off. However I cannot find such a command.