No abstract

To solve the problem of automobile rear end collision, an early warning system is designed, which is based on DSP chip control. Ultrasonic ranging is selected in the system. By providing pulse trigger signals, internal modules will send out eight periodic levels with forty kHz, and detect echoes at the same time. Once the echo signal is detected, the reverberation signal will be output. Then the reverberation signal can be changed into actual distance in real time by interrupt mode. The result stands for the distance between the car and the obstacles, then corresponding braking measures and early warning will be decided according to the minimum safety distance. When it is dangerous, the car status can be controlled according to the setting logic state.

After investigating the residual current protection and its major deficiencies, it is found out that the touch/Leakage current could be separated from the total residual current by the current separation technology , which is based on the phase relationship between normal residual current and touch/leakage current. A novel leakage current protection principle without protection dead-zone is proposed .The proposed method, which is put into practice on DSP , proves to be accurate and feasible in digital simulations. Compared to the existing techniques based on the residual current amplitude or its variation,the proposed method can eliminate protection dead-zone effectively and improve the reliability of protection devices drastically.