A backlight module includes a plurality of point light source generators, a diffusing plate installed on the plurality of point light source generators for scattering the light generated by the plurality of point light source generators, and a diffusing sheet installed above the diffusing plate for diffusing the light emitted from the diffusing plate. kn sensor units configured to output a plurality of signals whose period is one pitch and whose phases with respect to the pitch are different are arranged along the magnetic scale in a one-pitch segment. The symbols are mapped in the start position. The split spring of the invention may be used in MEMS devices for optical switches in order to provide independent voltages to the movable part in those devices.