The heading and attitude signal simulator is designed to provide a signal source that can be manually adjusted and controlled for the instrument equipment to be tested or laboratory research. It can generate various frequencies of heading and attitude signals and arbitrary waveforms defined by users, so as to test the aircraft performance. The traditional development of the heading and attitude signal simulation system is based on VXI, PCI and other bus, mostly using hardware circuit design and implementation, through the PC for analysis and processing, the function is relatively perfect, but the structure of the circuit is more complex, the volume is too large, it is not suitable for use in the outfield, and the traditional simulator is limited in the scope of use, resulting in the cost side So it is necessary to develop a new programmable universal simulator. In this paper, a portable attitude signal simulator is designed, which is not only small and easy to carry, but also uses DSP with high-speed data computing ability. It can preprocess, transmit, display and store the shaft angle signal of resolver. The system can be widely used in aviation, aerospace, radar, artillery control and other military equipment, but also can be used in CNC machine tools, robots and other civil equipment, and has a broad application prospect.

  Power supply design

DSP chip uses two different voltages, core 1.8V voltage and IO port 3.3V voltage, so it generally adopts dual power supply when supplying power to DSP system. In this design, tps767d301, a power supply chip specially provided by TI company for DSP, is used to provide power supply. This chip is a linear DC / DC converter chip, which can produce 3.3V power supply meeting F2812 by providing 5V DC power supply to tps767d301 In addition, the maximum output current of the power chip can reach 1 A, which can supply power to the DSP chip and a small number of peripheral circuits at the same time.

  Clock and reset circuit

The clock of DSP2812 chip has two pin connection modes. One is to connect a crystal between its X1 / XCLKIN and X2 pins by using its internal crystal oscillator circuit to start the internal oscillator; the other is to directly input the external clock source to the X1 / XCLKIN pin, and the X2 pin is suspended. The first method is adopted in this design, as shown in Figure 3.

  Circuit design of DSP heading and attitude signal simulator

DSP2812 chip has PLL clock module, which can input clock for frequency doubling, so it uses 30 MHz external crystal oscillator, after PLL frequency doubling, it can achieve 150 MHz requirements of the system. Because the power module tps767d301 chip can generate reset signal, and the reset signal can be directly used by DSP chip, so there is no special reset chip in this design.

  Working principle of converter chip and design of its interface with DSP

The 12sxz conversion chip consists of five parts: reference transformer, quadrant selection switch, sine cosine multiplier, power amplifier and output transformer. After sine and cosine multipliers, digital total angle and reference signal input are converted into sine and cosine signals representing angles. After amplified by power amplifier, it has a load capacity of 1.3va. After isolation and boost by output transformer, it becomes three wire and four wire analog signal output in the form of synchro / resolver.

Where the left side of the equation is the output voltage, θ is the input digital angle, K is the scale factor, and urh-rl is the reference voltage. The working principle block diagram of the converter is shown in Figure 4.

  Circuit design of DSP heading and attitude signal simulator

The core of the simulator is DSP 2812, which can generate the required heading and attitude signals through software control, and the system has self-test function. In the system design, DSP controls I / O port to directly operate 12sxz to generate analog signals. As we know above, DSP has two kinds of voltage. The voltage of I / O port is 3.3 V, and the conversion chip we use is 5 V of TTL level. Considering the driving ability of DSP to generate signals, we need level conversion first to convert the 3.3 V level of DSP port output to 5 v. The adopted level conversion chip is sn74alvc164245, which is a 16 channel bidirectional level conversion chip, and its conversion direction is controlled by pin dir. The conversion chip SXZ is a 12 bit converter, which is connected with the 12 channels of the level conversion chip through the data ports d0-d11 of DSP. The converted 12 bit level is connected with the 12 bit word input terminal of SXZ. The interface circuit between DSP and 12sxz converter is shown in Figure 5.

  Circuit design of DSP heading and attitude signal simulator

This paper introduces the hardware design circuit of the heading and attitude signal simulator based on DSP technology. This method overcomes the shortcomings of the traditional simulation technology, such as complex structure, low precision and poor reliability. The heading and attitude signal can be realized by software programming. Through the development, debugging and application of the simulator, the simulator has the advantages of low power consumption, small volume, etc., which is convenient for on-site debugging, and can be used in a variety of environments. It can greatly improve the troubleshooting, maintenance of aircraft safety and improvement of flight quality.

The core control chip is TMS320F2812, but the basic peripheral circuit must be provided to play the role of the core control circuit. A typical minimum system of DSP should include DSP chip, power supply circuit for DSP chip, reset circuit for triggering DSP initialization, clock circuit and JTAG interface circuit for online simulation and download. In addition, considering the need to communicate with the host computer to complete the transmission of data and control signals, a serial communication circuit is added. The basic system block diagram of DSP is shown in Figure 2. The external RAM is used to store a large amount of signal data, and the external flash is used to store the control program.

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