The reversing anti-collision alarm system designed by this scheme adopts the combination of software and hardware, and has the characteristics of modularization and multi-use. The development and basic principles of ultrasonic testing are introduced in the design, and the principle and characteristics of ultrasonic sensors are described. Some main parameters of the system are discussed, and based on the introduction of the function of the ultrasonic ranging system, the overall composition of the system design is proposed. The proposed scheme will generate active collision avoidance and even automatic driving for the driver, and provide the driver with a Reverse operation instructions.
As we all know, to detect whether there is any obstacle between the two ends, the general practice is to send a signal at one end, and judge whether there is a signal received at the receiving place. If there is a signal received, it means there is no obstacle in the middle; if it is not received, it means There are obstacles. However, in the design of the car reversing anti-collision alarm system, since the car is a moving object, it is impossible to install the receiving or transmitting device at a specific position, which determines that the transmitting and receiving devices of the system must be installed together. Therefore, how to design an object detection device that mounts the transmitting and receiving devices is our research direction.
2. Introduction of ultrasonic ranging system
Ultrasonic ranging can be divided into two types: resonance type and pulse reflection type. Due to the application requirements, pulse reflection is used here, that is, the reflection characteristics of the ultrasonic waves are utilized.
The principle of ultrasonic ranging is to transmit ultrasonic waves in a certain direction through an ultrasonic transmitting sensor, and start timing at the same time as the transmitting time. The ultrasonic waves propagate in the air, and immediately return to the obstacle when the obstacle is encountered on the way, and the ultrasonic receiver stops counting when receiving the reflected wave. . The propagation speed of ultrasonic waves in air at normal temperature is C=340m/s. According to the time t recorded by the timer, the distance (S) of the emission point from the obstacle can be calculated, namely:
It can be seen that the main parts are: (1) a pulse generator (transmitting circuit) that supplies electrical energy; (2) a switch portion that isolates the receiving and transmitting; (3) converts electrical energy into acoustic energy, and transmits acoustic energy to the medium. a transmitting sensor; (4) a receiving sensor that receives reflected sound energy (echo) and converts the sound energy into an electrical signal; (5) a receiving amplifier that amplifies the weak echo to a certain amplitude and causes the echo to excite the recording device; (6) A recording/control device that typically controls the power delivered to the sensor and controls the time at which the echo is recorded, stores the required data, and converts the time interval into a distance.
3. Overall system design
The system mainly uses electromagnetic output and input oscillation circuit. The input signal is amplified and sent directly to the AT89C2051 for processing. It can be automatically controlled by programming. The specific principle block diagram of the system is shown in Figure 3.1:
The system is mainly composed of the following three functional blocks: ultrasonic sensor T/R40-16, ultrasonic transmitting and receiving transceiver system; central control processor AT89C2051 host system; control alarm output system.
The main system circuits are: power circuit, ultrasonic transmitting circuit, ultrasonic receiving circuit, signal amplifying circuit, DC control circuit, display circuit, detection distance selection circuit, alarm circuit, and single-chip control circuit.
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