A combine harvester vehicle having threshing, separating and cleaning stages for cut crop material and a tailings return elevator for conveying tailings to one of the stages for recycling, is provided with a tailings monitor including a photodiode for transmitting a radiant energy beam across the path of tailings being conveyed in the elevator, an electrical circuit including a photodetector for deriving digital signals indicative of whether the beam is impinging on the photodetector or is being interrupted by the tailings, and an RC circuit which charges a capacitor through a resistance when the digital signal is present indicating that the beam is interrupted and discharges it when the opposite digital signal is present to thereby develop an average voltage across the capacitor which is an analog of the percentage of time that the beam is interrupted by the tailings being conveyed in the elevator and can be visually displayed on a voltmeter to the combine operator as a measure of tailings volume. In an alternative embodiment the digital signals are coupled to a microprocessor for processing of the signals and display to the operator.