2.2. Control unit
The control unit of the PDU encompasses the modules and functionality that allow for intelligent control of the optics unit, targeted spraying and external communications with the PDU.
2.2.1. Microcontroller
To perform successful discrimination and targeted spraying in real-time at adequate farming vehicle speeds, all requisite data acquisition and calculations must be completed within a fixed time frame. Failure to do so would mean that the system could inadvertently spray crops and not detected weeds.
For a collimated beam diameter of 4 mm, the processing time was constrained by the fact that on performing a measurement, the microcontroller must complete all calculations before the platform moves forward by 4 mm to the next measurement position. Fig. 9 shows the constrained processing time versus vehicle speed, for a 4 mm collimated beam diameter. It is clear from Fig. 9 that, for an initial target vehicle speed of 10 km/h, a processing time of 1.440 ms per discrimination cycle is required.
The microcontroller chosen to meet the processing time requirement was the Microchip dsPIC33F, which is a 16-bit, 40 MIPS digital signal controller with a modified Harvard architecture and direct support for both integer and Q15/Q30 fractional arithmetic. Theoretically, the microcontroller was capable of executing 57,600 instructions in 1.440 ms, which proved adequate for the low overhead discrimination algorithm, written in the C programming language
2.2. Control unitThe control unit of the PDU encompasses the modules and functionality that allow for intelligent control of the optics unit, targeted spraying and external communications with the PDU.2.2.1. MicrocontrollerTo perform successful discrimination and targeted spraying in real-time at adequate farming vehicle speeds, all requisite data acquisition and calculations must be completed within a fixed time frame. Failure to do so would mean that the system could inadvertently spray crops and not detected weeds.For a collimated beam diameter of 4 mm, the processing time was constrained by the fact that on performing a measurement, the microcontroller must complete all calculations before the platform moves forward by 4 mm to the next measurement position. Fig. 9 shows the constrained processing time versus vehicle speed, for a 4 mm collimated beam diameter. It is clear from Fig. 9 that, for an initial target vehicle speed of 10 km/h, a processing time of 1.440 ms per discrimination cycle is required.The microcontroller chosen to meet the processing time requirement was the Microchip dsPIC33F, which is a 16-bit, 40 MIPS digital signal controller with a modified Harvard architecture and direct support for both integer and Q15/Q30 fractional arithmetic. Theoretically, the microcontroller was capable of executing 57,600 instructions in 1.440 ms, which proved adequate for the low overhead discrimination algorithm, written in the C programming language
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