The system under consideration is a DC motor drive system consisting of a separately excited DC machine supplied from a DC-chopper and controlled through a microprocessor trainer. In this part of the study, the suitable control loops and their digital controllers are designed. The study is continued in a second part (Part II) of this article where the complete structures of the hardware and the software are discussed. It is desirable to optimize the efficiency of the overall system and at the same time to obtain a satisfactory transient response of the speed. In the method used, the ratio of the armature current and the field current (Ia/If) that gives the maximum efficiency of the DC motor is analytically derived and the error term of the current ratio is controlled to be zero at steady state speed of the motor. However at the transient state, the efficiency of the proposed method is not optimal, but the satisfactory transient response is expected in compensation for the non-optimal transient efficiency. This characteristics is desirable. because the instantaneous value of speed is important. On the other hand, the integral value of efficiency is more important than its instantaneous value.