Everyone knows how to calculate the resistance of a current limiting resistor for a LED but is it possible to go the other way? (aka determine the supply voltage from the resistor's value)
I ask this because I am working on re-purposing ink jet printer parts for low cost 3D printers to be built in developing countries. Ink jet printers used to use stepper motors but recently have started using DC motors with optical quadrature encoders. In order to use the e-waste one must find the voltage at which the quadrature encoders are supposed to operate at. While the forward voltage of the LED isn't known, is it possible to determine a ballpark idea of what voltage should be used to power the LED in the quadrature encoder?