Apparatus for automatic guidance of a trackless vehicle

In order to permit digital processing of the alternating signals induced in a pair of perpendicular detecting coils mounted on a trackless vehicle which is guided over a buried guide cable carrying alternating current, one of the induced signals is phase shifted and applied to one input of a comparator whose other input receives the other signal. At the same time, the other signal is also fed to a comparator which produces a rectangular output signal in phase with the original signal. The outputs of the two comparators are fed to a microprocessor which generates an error signal related to the time interval between the occurrence of periodic features of the two input signals. The error signal is used to engage the steering gear of the vehicle to return it to its path over the guide cable. In further embodiments, the frequency of the input signals is lowered to facilitate digital processing and a separate counter is used to uncouple the microprocessor from the detection apparatus, permitting it to process the data at a lower frequency of operation.