Realization of electronic delay detonator based on AVR

　　Electronic detonators are generally divided into three types: (1) electrically initiated programmable electronic detonators, where the delay time is set at the blasting site according to the blaster's requirements, and the detonation sequence of the entire blasting system is programmed on site; (2) electrically initiated non-programmed electronic detonators, where a fixed delay time is pre-set in the factory; (3) non-electrically initiated non-programmed electronic detonators, where the electronic delay body can be triggered by non-electric initiating equipment such as detonating cords or low-energy detonating cords, and then detonated with a fixed delay time pre-set in the factory [1-2]. The ability to easily form a simple and advanced detonation network is a major advantage of electronic delay detonators. This scheme provides a design method for an online programmable electronic delay detonator.

　　1 Electronic Delay Detonator

　　Electronic delay detonator is a new type of electric detonator that can arbitrarily set and accurately achieve delayed ignition time. Its essence is to use a microelectronic chip to replace the chemical delay medicine and electric ignition element in ordinary electric detonators, which not only greatly improves the delay accuracy, but also controls the power supply to the ignition head, thereby minimizing the delay error caused by the energy demand of the ignition head.

　　The structure of the online programmable electronic delay detonator designed in this scheme is shown in Figure 1.

　　2 Control Circuit Hardware Design

　　Electronic delay detonators use a control circuit board to replace the chemical delay agent in ordinary electric detonators. This not only greatly improves the delay accuracy and reduces the damage caused by blasting vibration[1], but also improves the anti-interference ability of the detonator through the control circuit.

　　The block diagram of the control circuit board designed in this scheme is shown in Figure 2.

　　The control circuit chip is mainly composed of an intelligent control unit composed of an AVR single-chip microcomputer, a rectifier circuit, a charging control and charging circuit, a safe discharge circuit, a detection conversion circuit, an ignition control circuit, a communication interface circuit, a power management circuit, etc. Information can be exchanged with the detonator through the communication network. If the ID of the electronic detonator sent by the receiving detonator is the same as the ID stored in the storage unit itself, it starts to receive the charging command, detection command, delay time setting, ignition command, etc. sent by the detonator and responds accordingly according to the command word.

　　2.1 Features of AVR MCU

    　In this design, the intelligent control unit is required to work safely and reliably, and to respond quickly and correctly after receiving the control command. At the same time, it is required to have rich internal resources (such as the requirement to integrate multiple frequency RC oscillators, power-on automatic reset, serial communication interface, watchdog, ADC conversion and other functions). In this way, the peripheral circuit can be relatively simple, and the system will be more stable and reliable during design [3-4]. Under the premise of meeting the above conditions, the price of the microcontroller is required to be low, and the price of the electronic detonator can be controlled [3]. Only in this way can the electronic detonator be truly put into large-scale production and widely used.

The AVR microcontroller selected in this design can meet the above requirements. It adopts Harvard structure, streamlined instruction set, fast execution speed, integrated with the functional circuits required by this design, rich internal resources, with E2PROM, PWM, RTC, SPI, UART, TWI, ISP, AD, Analog Comparator and WDT, etc., with high cost performance [4-5].

　　2.2 Control circuit function realization

　　The realization of the functions of each functional module of the control circuit is that after receiving the control command, the intelligent control unit responds accordingly by detecting the current state. For example, to charge the energy storage device: after the intelligent unit receives the charging control command, it outputs a control signal at the corresponding pin, so that the electronic switch in the charging control circuit is in a closed state, and the charging circuit charges the energy storage device outside the control circuit chip. When the charging time is up, the intelligent control unit sends a control signal to open the electronic switch in the charging control circuit. After charging is completed, the charging status is converted into corresponding data through the 10-bit AD conversion circuit of the AVR's A port through the detection conversion circuit, and then sent back to the control management layer through the communication interface to make correct decisions. [page]

　　3 Software Process Design

　　The software communication flow chart of the electronic delay detonator designed in this scheme is shown in Figure 3.

　　4 Security Analysis

　　The online programmable electronic delay detonator design proposed in this proposal uses a variety of security technologies, such as password technology, ID comparison, system detection, anti-interference technology used in the control circuit board, and the setting of a safe discharge circuit [6-8]. Therefore, it has high safety performance.

　　4.1 Security technologies used in the software

　　The detonator first sends the ID code of the electronic detonator to be selected, and compares it with the ID code fixed in each electronic detonator. Only when they match can various control commands be sent to the electronic detonator. Such software settings enhance the security of the system[6]. The controller can detect the current working status of each electronic delay detonator in the detonation network online, such as charging, delay time setting, etc., which should be sent back to the detonator in time for online monitoring. If the detection fails, the fault needs to be eliminated. The security technology adopted by these software improves the safety and reliability of the system.

　　4.2 Safety technology used in control circuits

　　The control circuit of the online programmable electronic delay detonator uses good anti-interference technology. A safety discharge circuit is designed in the control circuit of the electronic detonator. When the detonator receives the firing control command and does not fire after the delay time designed by the system, the AVR microcontroller detects the signal and sends a control signal to the safety discharge control circuit after a certain delay, so that the energy stored in the energy storage device after charging is consumed through the safety discharge circuit. The danger of subsequent processing work after the lost gun is eliminated. The control circuit board adopts an isolation circuit, so that the interference such as static electricity and stray current common in the engineering blasting network system cannot directly act on the ignition element of the detonator, which improves the inherent safety of the electronic detonator [2, 8].

　　The test results show that the programmable delay range of the electronic delay detonator designed in this scheme reaches 0 ms to 15 000 ms, the programming increment is 1 ms interval, the detonator delay time is long and the error is small. It is safe and reliable, with high delay accuracy, easy operation and use, and high cost performance. In short, the digital detonator represents a direction for the development of engineering blasting towards digitalization, and has application and promotion value in engineering blasting under complex environments such as strict vibration control requirements, precise time difference requirements between detonation sections, and long detonation time.

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