Working principle and application of infrared photoelectric detector in electrostatic target spray

Agriculture is the foundation of the national economy. Advanced plant protection technology is the guarantee of agricultural production and harvest. Modern plant disease and insect pest control is still dominated by chemical agents. my country's conventional pesticide application methods and pesticide application equipment are backward, and a large amount of pesticides are lost to water, soil and atmosphere. The utilization rate of pesticides is low, the cost of prevention and control is high, and it causes serious environmental pollution. The control effect on some pests is poor. The research and development of advanced pesticide application methods and pesticide application equipment plays an important role in the sustainable development of my country's agriculture, reducing production costs, and especially protecting the environment. Target spraying is a newly developed new technology for high-efficiency and low-pollution pesticide application. The "Tree-sense" smart sprayer developed by AGTECH uses the three-dimensional image sensor used in "Desert Storm" to detect enemy tanks. It can effectively spray according to the distance and shape of crops; DURAND WAYLAND's "Smart Spray" sprayer and "Tree-see" sprayer use advanced sonar systems to accurately locate the target. These devices are highly accurate but expensive. According to my country's national conditions, we designed an infrared photoelectric detector to detect targets, and combined with high-voltage static electricity to charge the droplets. The charged droplets fly toward the plants in a directional motion and finally adsorb on the plants, which significantly improves the hit rate. This infrared detector has low development cost, high sensitivity, and small size. When combined with static electricity, it can achieve basically the same effect as the above system.

Design Ideas
　　This article mainly describes the development of infrared photoelectric detectors. Infrared is an invisible light. The use of dedicated infrared transmitting and receiving tubes can effectively prevent interference from surrounding visible light, conduct contactless detection, and not damage the object being measured. The detector is installed on an electric trolley. Infrared target spray is mainly used in the seedling and growth period of cotton. When cotton is in the seedling stage, the cotton seedlings are scattered and easy to target. When in the growth period, the stems of cotton have a certain height. At this time, infrared rays are used to irradiate the stems and determine the target through reflection. Considering that cotton farmers pay great attention to field management and there are few weeds in cotton fields, the interference to infrared photoelectric detectors is very small and can be ignored.

　　Figure 1 Schematic diagram of infrared detector frame

　　Figure 2 Detection distance

　　Figure 3 555 state diagram

　　Figure 4 Directivity of infrared transmitting and receiving components

 

The design of infrared photoelectric detector 
　　is shown in Figure 1. The LM567 integrated phase-locked loop decoder and its peripheral components form a phase-locked circuit. The transistor V1, infrared emitting tube H1 and resistors R1 and R9 form an infrared emitting circuit. The oscillation signal of the phase-locked circuit is output from the 5th pin of the LM567 and sent to V1 for amplification, driving the infrared emitting tube to emit a square wave signal. The integrated circuit mA741, infrared receiving tube H2 and its peripheral components form an infrared receiving circuit. The infrared receiving tube H2 converts the received infrared signal into a change in its own resistance value, which is coupled to the 2nd pin of mA741 through resistor R3 and capacitor C3, and amplified by mA741. The 555 circuit, transistor V2 and its peripheral related devices form a delayed output circuit to control the opening time of the solenoid valve. When cotton is detected, the green LED lights up, the relay is energized, the normally open contact is closed, and spraying begins.
The infrared photoelectric detector detects cotton by infrared reflection. Within the set effective detection range, if there is no cotton, the infrared receiving tube cannot receive the reflected infrared light signal, the ⑧ pin of LM567 outputs a high level, the ③ pin of 555 outputs a low level, the transistor V2 is cut off, and the solenoid valve is closed and does not spray; when cotton is detected, the infrared receiving tube receives the infrared signal reflected by the cotton, which is converted by the conversion circuit and sent to the amplifier circuit μA741 for amplification. The amplified signal is sent to the ③ pin of LM567 to compare with its own oscillation signal. When it has the same frequency as its own oscillation signal, the ⑧ pin of LM567 outputs a low level, the ③ pin of 555 outputs a high level, the transistor V2 is turned on, the relay is energized, and the solenoid valve opens to start spraying.
　　In order to prevent false operation caused by interlaced detection, the effective detection distance L (L2) can be adjusted to ensure the opening time of the nozzle. The monostable delay circuit composed of 555, R7, and C9 is shown in Figure 1. The output pulse width of V2 is Tp0 = R7·C9·ln3≈1.1R7·C9. If there is an interference trigger pulse during the duration of the circuit's temporary steady state, the pulse will not work, as shown in Figure 3, which ensures the opening time of the solenoid valve. The output pulse width Tp0 can be adjusted by R7.
　　In infrared transmission and reception, it should be taken into account that both the transmitting element and the receiving element have directionality. Therefore, there is a position where the sensor can obtain the maximum sensitivity. In addition, there is a range in which the sensor can work normally, as shown in Figure 4.
　　Using the pulse signal of LM567 ⑤ foot to drive the infrared light-emitting tube, in addition to using the phase-locked loop decoder LM567 to improve the detection sensitivity and eliminate the interference of background light such as sunlight, it can also double the transmission power of the infrared light-emitting tube compared with the DC drive method when the average input power remains unchanged. Adding an infrared filter at the front end of the infrared detector can remove visible light and allow infrared light to pass, further improving the anti-interference ability.

Conclusion 
　　The biggest feature of this circuit is that it realizes the synchronous automatic tracking of the infrared emission and receiving working frequencies, that is, the infrared emission part does not have a special pulse generation circuit, but directly introduces pulses from the detection circuit of the receiving part (actually the phase-locked center frequency signal of LM567), which not only simplifies the circuit and debugging work, but also prevents the inconsistent receiving and transmitting frequencies caused by changes in the surrounding environment and component parameters, greatly enhancing the circuit stability and anti-interference ability. The detector achieved good results in the experiment, greatly improving the hit rate of the spray compared with non-target spray.