I'm currently working on a project that will (hopefully) incentive people to stop using disposable batteries. To do that I'm thinking on creating a dummy battery that will allow you to plug a powerbank with the right voltage and, therefore, powering the device.
I want it to be as dummy proof as possible (no pun intended)
The problem lies on the correct power supply versus the number of batteries in a circuit.
For example, a 4x AA device requires 6V.
I'm trying to find a way of limiting people from plugging a 9V power supply on that case... Or even getting the battery to correct the voltage automatically in a easy way. Is there a simple circuit that would allow me to "sense", in a more or less passive way, how many batteries there are in the circuit?
Do you have any idea on how I could acomplish that?
To clarify, Imagine the picture below. I want the smart battery to "sense" how many dummies are attached to it. This is a 4xAA example but it could be a 2x or even 6x batteries. (Diodes are just an attempt to prevent reverse polarity)