Abstract: A counter for seeds in a duct includes a first point source transmitter on a first mounting on one side of the duct spaced outwardly from the duct so as to project light through a front wall and a set of phototransistors in a transverse row carried on a second mounting on a rear wall. The side walls of the duct lie on a triangle with an apex at the light source. The phototransistors are connected in series so that the output current is determined by that phototransistor on which the majority of the shadow from the seed falls. In this way the momentary reduction in current output has a larger amplitude to better distinguish from dust in the duct. The duct is formed by a housing attached to the peripheral wall of the metering device with a seed transport tube attached to the bottom of the housing.

Abstract: A counter for seeds in a duct includes a first point source transmitter on a first mounting on one side of the duct spaced outwardly from the duct so as to project light through a front wall and a set of phototransistors in a transverse row carried on a second mounting on a rear wall. The side walls of the duct lie on a triangle with an apex at the light source. The phototransistors are connected in series so that the output current is determined by that phototransistor on which the majority of the shadow from the seed falls. In this way the momentary reduction in current output has a larger amplitude to better distinguish from dust in the duct. The duct is formed by a housing attached to the peripheral wall of the metering device with a seed transport tube attached to the bottom of the housing.