It is very important for the stability of the fixed star and satellite to accurately detect the turntable position and speed in the servo control system of the telescope turntable. The conventional incremental encoder is difficult to meet the requirement of tracking accuracy. In view of this,a kind of high precision steel ring reflective grating encoder( RESM20USA413) is adopted,which has a simple interface circuit with the ARM processor. Then the output signal of the encoder is optical subdivision and filt...