Get a CLD(Current Limiting Diode) you can get them in various currents from 400-microAmps to 10-milliAmps. You can put in several and have a swiych to choose what current level you wish. This is a very simple current control, you can build a variable one or like a one of mine takes 3 VDC to 36 VDC at 1.5milliAmps. With this one I can use AA/C/D for the power source-like when I am out camping.