Embedded UAV Control System Hardware Circuit—Chip Diagram Reads Everyday (146)
In the UAV flight control system, the flight controller is its core component, which is responsible for the acquisition of the flight control system signals, the calculation of the control law, the attitude and speed of the aircraft, and the communication with the ground equipment. With the increasing application of drones, the tasks it performs are becoming more and more complex, and the mobility requirements of drones are becoming higher and higher, which requires the control core of drones to be highly integrated. And the direction of miniaturization. This paper designs a flight controller for a certain type of UAV with the 586-Engine embedded chip as the core. The AMD Elan SC520 processor-based micro-control module features high reliability, compact structure and low power consumption. It also has powerful debugging software. The main parameters of the 586-Engine are as follows:
(1) The CPU is a 32-bit AMD Elan SC520 with a frequency of 133MHz. (2) It has a high-performance floating-point arithmetic unit that supports complex operations such as sine, tangent, and logarithm. It is ideal for applications that require complex operations. (3) Configure 512KB SRAM, 512KB Flash, 114 bytes internal RAM; (4) Support 15 external interrupts. There are 7 timers, including a programmable internal timer that provides three 16-bit internal timers and three 16-bit GP timers, plus a software timer. These timers support the timing and counting of external events. The software timer provides a microsecond hardware time base. (5) Provide 32 programmable I/Os and 2 UARTs. There are 19 12-bit A/D inputs, including 11 ADC serial inputs and 8 parallel ADCs. The conversion frequency is 300kHz; 6 D/A outputs. It includes 2 serial output DACs and 4 output parallel 12-bit DACs with a conversion frequency of 200kHz. (6) The working temperature is -40 ° C ~ 80 ° C, the size is 91.4 mm & TImes; 58.4 mm & TImes; 7.6 mm.
Flight controller hardware design
This type of drone is a medium-sized wheeled drone that provides communication relay for the naval field forces. Its flight controller is a small boxed small airborne electronic device, which is composed of DC/DC DC power conversion board and computer. The main board, the analog channel board, the switch channel board and the servo control board are all connected, and all the templates are connected by the bus on the motherboard to reduce the size and improve the integration.
The flight controller needs to communicate with GPS, magnetic heading meter and radio altimeter, and requires a total of 5 serial ports. The 586-Engine motherboard only provides two serial ports for ground detection and measurement and control stations, so serial port expansion is required. The serial port expansion circuit is shown in Figure 3.
The serial port expansion circuit uses TL16C754 four-channel UART parallel-serial conversion device to convert 8-bit parallel data into 4 serial outputs, plus MAX202 and MAX489 level conversion chips, and expands 2 RS232 serial ports and 2 RS422 serial ports. Meet the hardware requirements of the flight controller.
D/A conversion hardware circuit design
This type of UAV uses an analog servo, which requires a total of 6 D/A channels to generate a PWM signal to drive the servo. The 586-Engine mainboard provides a total of 8 D/A, of which 4 12-bit parallel D/A (DA7625) control the elevator, left and right aileron servos and rudder, 2 12-bit serial D/A (LTC1446) Control the front wheel servo and throttle servo. Since the output voltage range of the DA7625 is 0~2.5V, the LTC1446 output voltage range is 0~4.096V, and the servo operating voltage is -10~10V, so the signal needs to be amplified and level shifted. The D/A level shifting circuit is shown in the figure.
As can be seen from the figure, the D/A level shifting principle uses an adding circuit at the input end of the op amp to add the input signal to the reference level to obtain a voltage range suitable for sampling. Regarding A/D acquisition, the 19-channel 12-bit A/D interface on the 586-Engine main board fully meets the requirements of the flight control system channel number and conversion accuracy. These A/D interfaces respectively collect the data of the barometric altimeter, Man-machine load voltage, engine speed and temperature, throttle opening, etc. These signals are sent to the ground measurement and control computer, which provides the basis for the operator to monitor the working status of the drone. For I/O control, the 586- Engine motherboard provides 32 16-bit programmable digital I/O ports for collecting engine start signals, umbrella cabin open signals, etc., and outputting switch signals to control other devices to control the unmanned Machine take-off and recycling process.
Power module hardware circuit design
The power module circuit of the flight controller provides a clean and stable supply voltage to the flight controller to ensure that the flight controller is working properly. The design of the power module circuit directly affects the stability and reliability of the flight controller operation. Because of the certain size requirements and the reliability and cost, this type of drone is designed with a mature standard module power supply and can be operated with a small number of external devices. The flight controller power supply module circuit is shown in Figure 5.
Among them, 24T05D12 module power supply is used as the main chip of the power supply circuit, the power is 30W, the input voltage range is 18V~36V, and there are three power supply outputs: +5V and ±12V to supply power to the onboard sensor and servo. The use of the embedded chip reduces the size and weight of the flight controller, and achieves the design goal of miniaturization and high integration of the flight controller; the self-designed serial port expansion circuit and the servo control board reduce the development cost and meet the requirements. The requirements of the project demand side. It is foreseeable that the unique features of the 586-Engine and the high cost performance will be widely used in the field of UAV flight control.
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