introduction This article refers to the address: http:// Birds play an important role in the ecological balance of human living environment. Humans take various measures and formulate regulations to protect them, but the rapidly increasing number of animals poses serious harm to agricultural production, resulting in a decline in the output and quality of agricultural products. . According to incomplete statistics, more than 98% of the orchards in the country have suffered from bird damage, and the direct economic losses caused each year are as high as 700 million yuan. In recent years, in response to the problem of bird damage, some methods of driving birds have been studied at home and abroad, mainly the sound drive and image drive. Among them, the principle of bionics is used, and a series of biologically meaningful sounds, such as the sound of a raptor, a bird's death or an alarm call, is used as a means of control. In this paper, the digital voice bird repeller array is used to realize the sound field focusing by the beamforming method, and the sound field of the drive sound chain is controlled in the desired area to achieve good bird repellent effect. Sound field focusing principle At present, the sound field focusing is mainly realized by two methods: time delay (TD) and maximum control gain (MCG). The TD method adjusts the phase of the transmitted signal of each unit according to the delay difference introduced by the difference of the distance between each speaker unit and the target point, so that all the received signals at the target point are superimposed in phase to obtain the maximum sound pressure intensity, as shown in FIG. Show. The MCG method not only considers the delay difference of all received signals, but also considers the amplitude fading difference, and adjusts the amplitude and phase of the transmitted signal of the array element to achieve the sound field focusing at the target point. Design of Digital Voice Bird Repellent Array System In order to effectively drive the birds in the orchard, a 6-way bird repeller array system was designed. The system performs weighting on the phase adjustment of the voice digital signal. After digital-to-analog conversion, the multi-channel speaker output is driven by a power amplifier. 2 is a block diagram of a digital voice bird repeller array system. After the on-site central controller acquires the position information of the invading bird, the weight value of the sound chain is calculated according to the position information of the bird repeller array speaker, and the weight value information is transmitted to the microcontroller through the serial bus, and the microcontroller gives The driving strategy of driving the sound chain is adjusted, and the phase of the array signal is adjusted. By controlling the address generator and the power amplifier switch, the pre-stored digital sound chain is converted by the DAC and played to achieve the purpose of sound field focusing. Sound chain phase adjustment algorithm Assume that the digital sound chain signal can be expressed as: Where w is the frequency, A is the amplitude, and j is the phase offset. Weight, weighted digital sound chain signal is: The amplitude and phase adjustment of the signal is implemented according to the method of quadrature modulation. Known weights: IQ double-channel amplitude and phase modulation for the sequence x[n] can be obtained: among them Bird repeller array distribution design The position of the speaker should be able to make any position in the sound field coverage area. The reasonable speaker position design can effectively control the sound field distribution of the speaker and the sound pressure level requirement of the projection distance, and also help to form the sound focus area to achieve better. Bird repellent effect. According to the maximum sounding distance L and the pointing angle a of the speaker, the effective coverage area of ​​a single player is determined: Considering that the total cost of the device is minimized and the cost of a single bird repeller is fixed, the minimum number of speakers needs to be determined. This value is closely related to the total area of ​​the control area, the effective area of ​​a single speaker, and the spatial distribution of the player, thus establishing an objective function relationship: Conclusion In order to improve the effect of the voice bird repeller driving the bird, this paper gives the design of the digital voice bird repeller array system and the sound chain focus field realization method, and explains the realization of the hardware circuit in detail. The sound field focusing is achieved by adjusting the phase of the sound source array of the digital sound chain, and the indoor experiment has achieved good results. Due to the complex situation around the orchard site, there is still a lot of work to be done in the next field. Here N is the number of speakers; S is the total area of ​​the control area; s is the effective area of ​​a single speaker; xi, yi is the coordinate distribution of the i-th speaker in the control area. Solving the objective function to obtain the theoretical position distribution provides a basic reference for the actual arrangement of the bird repeller array. Bird repeller array system hardware implementation The digital voice bird repeller array system consists of a microcontroller, an address generator, a memory, a DAC, a power amplifier, and a speaker. The microcontroller completes the delay difference calculation, phase weight adjustment, playback and synchronization control of each module of the voice sound chain. The address generator consists of two 12-bit calculators that are used to generate the address signals of the speech memory chip. The count clock of the address generator is provided by the microcontroller. A digital voice signal for driving the bird is pre-stored in the memory. The DAC converter converts the digital voice signal into an analog signal that is amplified by the power amplifier to drive the speaker array. The microcontroller uses Microchip's PIC18F6527, which is rich in interface modules to meet the system's functional requirements. The voice memory is AMD's AM29F032B, which has a capacity of 32Mbit and is stored and processed to drive out sound digital signals. The DAC uses an 8-bit AD557 for digital-to-analog conversion. The post-stage power amplifier is National Semiconductor's LM4950, which can drive 7.5W speakers. Because the whole hardware system adopts low power consumption, modular design, and sleep function, the system is easy to use and easy to maintain. Currently, the system has completed laboratory debugging. DELL Latitude Series,DELL Latitude,dell latitude 3420,dell latitude 3520 S-yuan Electronic Technology Limited , https://www.syuanelectronic.com
. The weighted digital signal can be calculated by: 
