1467966 Automatic control of seed planters DICKEY-JOHN CORP 26 April 1974 [18 June 1973] 18381/74 Heading AID [Also in Division G3] In order to keep constant the number of seeds per unit area sown by a planter comprising a seed dispenser 13 fed from a hopper 11, the number of seeds planted is counted by a sensor 14 and the ground speed of the planter is measured by a sensor 23, corresponding signals being fed to an electronic circuit which adjusts the speed of motor 32 driving the seed dispenser if the seed density' is not equal to the value set on a selector 25. As shown the two sensors are a photoelectric sensor and a wheel and produce pulse trains which are fed to respective inputs of an up-down counter 22, the distance pulses being fed via a divider 26 which is set by switches 25 to the desired planting density. The output of the counter 22 is converted to an analogue signal and used to control a servo valve 29 in circuit with the motor 32. The latter is a hydraulic motor supplied from a pump driven by tractor 10. When the tractor is stopped, a circuit 27 detects the absence of distance pulses and opens a bypass valve 31 to prevent creeping of the dispenser motor. If the distance pulse rate exceeds the planting pulse rate sufficiently to return the counter 22 to zero, a "clear" pulse is derived from the counter via an inverter (64, Fig. 3 not shown) and clears the counter to prevent the next down pulse producing a full count and closing the valve 29.
