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A simple air data computer UAV Design


F10 again like the process of implementation according to the formula (7) I open compute cycles interrupt and resume site map 3F / D interrupt service routine flow chart of the software has two tasks: first, the internal registers through FDC9201 access and correct operation,[link widoczny dla zalogowanych], the control FDC9201 complete high-frequency, low-frequency synchronization of the counter and get synchronization time of high and low count; the second is based on the resulting high and low counts measured by the formula periodic low frequency signal or frequency. 3.2 Data Solution Module pressure altitude and airspeed are the atmospheric air pressure, static pressure and large single-valued function, but its functional relationship is more complex, more difficult to calculate single chip, coupled with the unmanned aircraft air data system real-time requirements (that is to be completed within tens of milliseconds of data sampling, conversion, processing and output), therefore, the accuracy of the system requirements, AT89C52 microcontroller's memory capacity and the purpose of computing the actual situation, we have chosen equidistant line linear interpolation method to calculate the pressure altitude h. And IAS. The specific method is, F / D conversion cycle, the value obtained through the transformation of quantities, are atmospheric static pressure, it is a three-byte number stored in the RAM-30H ~ 32H; by calculating, h the sub-point interval to 50m, so, 0 ~ 100001TI height range can be divided into 200 intervals, and the various sub-points P, p, P a, P. . And the corresponding pressure altitude h coefficient k in accordance with the law constitutes a form must be stored in the microcontroller's internal ROM; formula calculated from the look-up table h. Calculated the same way according to equation (5) to calculate the true airspeed. In order to validate the performance indicators of air data computer, specifically designed for data display modules. The module is used as MAXIM's MAX7219 chip display driver circuit. MAX7219 has a serial interface chip is an 8-bit LED display drivers, because it is way serial microcontroller interface, and can be cascaded, so use it to design the display driver circuit, the circuit is simple, easy software programming, power consumption, only takes a few I / O lines, to meet system design requirements. Because the UAV air data system, the need to display five pressure altitude data, four 4-bit instruction data and the true airspeed airspeed data, therefore, a total of 13 digits to be displayed. The MAX7219 drives up to an 8-bit LED digital tube, so the display module 7219 using two cascaded way to drive. 4 Summary results of air data computer system the scope of work: a high degree of 0 ~ 10000m, space velocity of 50 ~ 40km / h. By the experimental conditions, the use of analog sensor input method in a certain height and airspeed within the experiment. Because height and airspeed use linear interpolation look-up table, according to the required accuracy has been calculated, the interval between points is set to a high degree of 50nl, airspeed set the interval point 5km / h. Randomized trial nearly 1,000 times, each interval of 4 to 5 times interval experiment. Derived from the atmospheric data to the table with real atmospheric data calculated by the system, air data parameters measured were compared with experimental results is good. A high degree of error is ± 51TI, altitude display resolution is 0.11TI; airspeed error of ± 0.5km / h, showed resolution is 0.1km / h. Errors mainly come from the F / D conversion precision and linear interpolation look-up table interpolation point selection interval,[link widoczny dla zalogowanych], and the interference within the system Suozhi. 5 Conclusion discussed above that, simple UAV air data computer is characterized by small size, simple structure, compact design and reasonable. Calculated by linear interpolation look-up table UAV air data parameters,[link widoczny dla zalogowanych], a very good real-time, to meet the UAV altitude and airspeed and output real-time solver, it is suitable for use in small UAVs. References F1] Yang are. Aviation Test System [M]. Beijing: National Defence Industry Press, 1984. [2] Xiao Jiande. Air data computer system FM]. Beijing: National Defence Industry Press, 1992. [3] Wang Qi, et al. FDC9201 low-frequency signals in the airborne high-precision measurement [J]. Optics & Control,[link widoczny dla zalogowanych], 2002, (2): 63 ~ 65. [4] Zhao Jianqiang, et al. V / F Conversion Technology in Tracking Control [J]. Machinery Industry Automation,[link widoczny dla zalogowanych], 1998, (6): 48 ~ 50. [5] Han Xiaodong, et al. V / F conversion in the SCM system [J]. Application of Electronic Technique, 2000, (2): 7 ~ 9. [6] Fujui Wang. Single-chip microprocessor control system design Daquan FM]. Beijing: Beijing Aerospace University Press, 1999.

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