Abstract: A programmable lawn mower assembly (10) including a carriage (12) supporting a mower central processing unit (CPU) (24) for controlling the drive motors (18) to control the direction of movement of the carriage (12). The assembly (10) includes first and second locating transmitters to be disposed on posts in spaced positions about the lawn with each locating transmitter simultaneously transmitting a radio frequency signal which travels at a first velocity and an audio signal which travels at a second velocity slower than said first velocity. A carriage receiver (50, 52) is disposed on the carriage (12) for receiving the radio and audio signals from the locating transmitters and for providing signals to the CPU (24) for determining the position of the carriage (12) relative to the locating transmitters by measuring the time between said radio and audio signals from each locating transmitter.

Abstract: A vehicle central processing unit (CPU) (50) controls the power unit (16 or 18) to control the direction of movement of the carriage (12) of a lawn mower for determining the position of the lawn mower relative to locating stations (36, 38 and 40) in response to the time of movement from the counter (54) of the distance determining transmissions between the transceivers (42) at the locating stations (36, 38 and 40) and the lawn mower.