Abstract: In an agricultural tractor having an engine for driving a PTO assembly through a PTO clutch, an interlock circuit includes a microprocessor, a relay and a PTO control switch. The PTO switch controls energization of the engine starter and PTO clutch actuator. The arrangement is such that the engine can be started only when the switch is off and the PTO clutch actuator can be energized only when the switch is on. The microprocessor senses the position of the switch and the speed of the engine and initially energizes the relay to connect battery voltage for energizing the clutch actuator to the switch only when the switch is off and the engine speed is within a predetermined range. When the relay is energized, the clutch actuator may be energized by turning the switch on. If the switch is turned off, the engine speed must be brought back within the predetermined range before the clutch actuator may again be energized.

Abstract: The fuel tank of a mobile vehicle is provided with a level sensor for sensing the level of fuel in the tank as it is being filled. The output signal from the level sensor is applied to a microprocessor which in turn provides output signals to drive an audible alarm and a visual display. The microprocessor determines the level of fuel in the tank from the signal produced by the level sensor and drives the audible alarm to provide a first sound pattern, such short beeps or tones when the tank is at least 3/4 full but less than 7/8 full and a second sound pattern such as a continuous tone when the tank is at least 7/8 full. The microprocessor also drives a visual display to display text messages indicating the level of fuel in the tank. A vehicle operator may initiate filling of the tank and attend to other service on the vehicle, leaving the fill operation unattended. The first sound pattern warns the operator that he must soon give his full attention to the fill operation.