Design of Mortar Anti-reloading System Based on Single Chip Microcomputer Control

    During the live-fire shooting of mortars, it is common for mortar shells to misfire. If a mortar shell does not fire, it is strictly forbidden to reload the shell. If it is reloaded, it is easy to cause a chamber explosion, resulting in serious casualties. How to determine whether a mortar shell does not fire and prevent reloading? At present, the gunner usually relies on observing the muzzle or listening to the firing sound to determine whether the shell has been fired. This method of observation and judgment is unreliable. During live-fire shooting, the gunner is highly nervous, which often leads to inaccurate observation results. For this reason, this system is designed to prevent reloading and avoid major accidents.

1 System Features
    At present, the mortar anti-reloading devices developed at home and abroad are mainly mechanical and electronic. This system is a combination of electromechanical. The system will only start the mechanical device when it detects that the loaded shell is stranded, making the process of reloading the shell impossible. The purely mechanical device will start the mechanical device through gravity during the loading process, which will have a certain impact on the loading operation. In the firing process, the shell will reset the mechanical device. If the mechanical device is not designed well, it will also have a certain impact on the trajectory of the shell, resulting in a decrease in shooting accuracy. The purely electronic device can only detect the retention of the shell and alarm, but cannot prevent the shell from being loaded again.
    This system uses infrared sensors as a means of detecting the shell entering and leaving the chamber. A certain space is extended outward along the diameter direction of the muzzle (try to avoid high temperature), and two infrared transmitting and receiving devices are installed at a certain distance above and below. Compared with the acceleration reset sensor or self -inductive variable resistance sensor used in other anti-reloading devices, the detection device has a simple structure, convenient installation, and high cost performance. In order to improve reliability and prevent mutual interference between the two channels, the infrared transmitting and receiving tubes are covered with tube sleeves to reduce scattering. At the same time, in order to avoid the reflection of infrared by the shells, the transmitting tube and the receiving tube are installed on the same side, as shown in Figure 1.

    This system uses a single-chip microcomputer as the core control circuit. Compared with the anti-reloading device composed of general circuits, the circuit is simpler, the debugging is faster, and the software programming-based function is more powerful and easier to expand. This system can judge the half-filled state of the shell, so when the firing is suspended and the shell is taken out again, there will be no false alarm. In addition, this system will start the sound and light alarm circuit only when the shell is not detected to be fired out of the barrel after 2.5 s after the shell is loaded. Most anti-reloading devices will alarm as long as the shell is loaded, and the alarm will be lifted after the shell is fired out of the barrel. The alarm will continue if the shell is not fired out of the barrel. Such a function setting will also have an alarm signal during normal operation, which artificially deepens the fatigue of the gunner. When the alarm continues when the shell does not fire, the gunner's sensitivity and vigilance will be weakened.

    2 Hardware Structure

    Figure 2 shows the hardware structure of the circuit control part of this system. According to the functional requirements, AT89C2051 launched by Atmel is selected as the control core. It is currently the most mainstream single-chip microcomputer chip with a total of 20 pins, including 15 I/O ports. Selecting this single-chip microcomputer can reduce the size of the device and simplify the circuit.

    To improve reliability, the signal emitted by the infrared transmitting tube is a 38 kHz modulation signal. The modulation circuit also uses AT89C2051 to generate a 38 kHz infrared modulation signal through software programming. The signal is increased in driving force through multiple parallel gate circuits and then loaded on the infrared transmitting tube (the modulation circuit of the transmitting signal is not shown in Figure 2). This not only makes the circuit simple, but also makes the signal frequency relatively stable. The
    infrared receiver uses an integrated receiving head HS0038, which integrates infrared receiving, amplification, demodulation, shaping and other circuits. When a 38 kHz infrared pulse train is received, a low level is output, otherwise a high level is output. The polarity of the output signal is opposite to that of the transmitted signal. In Figure 2, after using a triode to reverse and amplify it, the signals output by the two infrared receiving tubes are connected to the P3.2 ( ) and P3.2 ( ) pins of AT89C2051 respectively.
    The infrared sensor is a means of detecting the loading and firing of artillery shells, so the normal operation of its transmitter and receiver is a prerequisite for the reliability of the system. For this reason, a function of powering on to detect it is set.
    The single-chip microcomputer, as the control core, can determine the state of the mortar firing process according to the high, low and jump of the P3.2 and P3.3 input signals: waiting to be loaded, half loaded, completed loading, normal firing and misfire. When it is determined that the firing process is in the misfire state, P3.0 controls the start of the mechanical device to jam the muzzle to prevent the completion of the reloading action. At the same time, P3.1 starts the light flashing alarm and P3.4 starts the music KD9561 alarm. In order to increase the alarm sound, LM386 is used as an audio amplifier. When it is detected that a normal firing state is completed, the number of shells fired is calculated and displayed through the digital tube. The system sets a two-digit digital tube. The segment selection code is controlled by the P1 port of the single-chip microcomputer, and the bit selection code is controlled by P3.5 and P3.7. The maximum count value is 99.

    3 Software Design
    This system introduces the output signal of the infrared receiving tube into the P3.2 ( ) and P3.3 ( ) pins, the state of the mortar firing process can be judged by software programming in a clever and concise manner, because these two pins are both general I/O pins and external interrupt input pins. In this way, the state of the firing process can be judged by the high and low levels of the two pins and whether there is an interrupt and the order in which the interrupts are generated. When infrared light is received, P3.2=0 and P3.3=0, so when it is detected through query that P3.2=0 and P3.3=0, the firing process is in the
waiting state; when it is detected that P3.2=1 and P3.3=1, the firing process is in the half-filling state; with the half-filling state as the judgment premise, if the shell is taken out again, P3.3 will first change from high to low, and then P3.2 will change from high to low, that is, when the interrupts are generated successively, it means that the shell has been taken out and returned to the waiting state; on the contrary, when the interrupts are generated successively, it means that the shell has completely slid into the barrel and entered the filling completion state. At this time, the timer is started, 2.5 If no interruption is detected after s , it means that the shell has not been fired and has entered a misfire state; on the contrary, if the interruption is detected within 2.5 s , it means that a normal firing has been completed.

    Therefore, the software system consists of a main program, a display driver subroutine, two external interrupt service programs and a timing interrupt service program. The two external interrupt service programs complete the setting of the order variables indicating the order in which the two interrupts are generated and the setting of the discharge mark. The timing interrupt service program completes the 2.5 s time timing and determines whether the shells are normally discharged from the barrel. Otherwise, an alarm is issued and the mechanical device is driven to work. The main program is first initialized, and then the state of the launch process is determined according to the high and low levels of P3.2 and P3.3 and the mark variables formed in the interrupt program. The program flows are shown in Figures 3 to 5.

        4 Conclusion

    This system uses a 20-pin single-chip microcomputer as the main control circuit and realizes system functions through software, making the entire system simple in structure, reliable in function, and easy to expand in function; using infrared sensors as the detection method overcomes the problems of similar devices affecting the mortar shooting accuracy, inconvenient installation and use, and the possibility of false alarms. It solves the problem of being unable to judge whether the mortar shells are fired out of the barrel after loading due to human factors during the firing process, avoiding the occurrence of potential major accidents.

    The control circuit and mechanical device are integrated into one, the appearance is designed to be arc-shaped, and the device is installed on the muzzle with a clamp. Through the test of live ammunition shooting, this system does not affect the loading and firing of shells, and the operation is reliable. When simulating a shell reloading accident, it can reliably and promptly alarm.