US Patent 7583561 Feed detecting system

A feed detecting system includes a sending element, a receiving element, a filtering-amplifying circuit, a peak-holding circuit, an A/D converter and a processing unit. The receiving element receives an ultrasonic signal sent by the sending element, and then outputs an electric signal, the filtering-amplifying circuit receives, filters and amplifies the electric signal, the A/D converter converts the electric signal to a digital signal, the processing unit reads the digital signal and compares the digital signal with a standard value stored in the processing unit. In this present invention, the A/D converter can be a low frequency A/D converter, so the cost of the feed detecting system is reduced.