The system design and evaluation of a microprocessor-controlled dispenser using a radar ground-speed sensor

This research focused on the design of a new approach to control seed dispensers and to analyze the performance characteristics of a Doppler radar ground speed sensor for a microprocessor control dispenser. The research focused on comparing the effectiveness of using a radar unit with a fifth-wheel encoder for measuring ground speed when both were connected to a microprocessor controlled seed dispenser. The system designed for this study consisted of hardware and a computer program in 6502 assembly language. The hardware for this study consisted of a monitor device, microprocessor control unit, stepper motor, fifth-wheel encoder, Doppler radar and the device for the planting of seeds. Laboratory tests were conducted to determine the accuracy of the microprocessor based speedometer, seed spacing control and the output waveforms from the Doppler radar and the fifth-wheel encoder under controlled conditions. Field tests were conducted to test the accuracy and variability of the seed spacing control under actual conditions. There was a significant difference between the mean indicated ground speeds of the Doppler radar and the fifth-wheel encoder controlled dispensing devices when an input signal was varied from 1 Hz to 574 Hz to the control box. The Doppler radar was more sensitive to frequency changes than the fifth-wheel encoder. Under the laboratory tests, without considering the slippage of the wheel, there was no significant difference between using the fifth-wheel encoder and the Doppler radar as sensors in dispensing seed at a uniform spacing. In the field tests, the Doppler radar controlled unit dispensed seeds at a more uniform spacing than the fifth-wheel encoder control unit. The Doppler radar provided a less variable output signal than the fifth-wheel encoder. During the field test, the researcher observed that one problem of using the Doppler radar unit was the slight vibration of the Doppler radar caused by the engine of the tractor. This caused some erroneous input signals to the microprocessor control unit because the monitor displayed a fractional part of a ground speed (MPH) while the tractor was stationary. (Abstract shortened with permission of author.