I am building a charging station for a variety of handheld devices, and one of the features I would like to add is some type of LED indicator that changes color when a device is fully charged. The charging cables need to be removable so one option I was considering was measuring the current at the power-strip outlet since the current would drop when the device is charged. I have no idea how feasible this would be since I am relatively new to Arduino.
Any guidance on how to accomplish this or ideas for other approaches would be much appreciated.
In order to not disturb the charging I suggest letting the current pass through a copper coil and using Hall device degect tve magnetic field in the coil.
Different battery chemistries have different charging characteristics, the way you determine if the battery is fully charged is different for each chemistry. To provide chemistry specific advice requires knowledge of which chemistry of battery you are proposing to charge.