Ultrasonic Range-Finding System Based On HT46F49E

Ultrasonic is unacted on the light, color, electromagnetic radiation and so on, and can adapt to the severe environment. So nondestructive testing (NDT) technologies based on ultrasonic are more and more popular, the ultrasonic ranging technology is one of them. Various kinds of rangefinders appear in the market, but the ultrasonic one has its unique advantages to occupy a place in the market.In recent years, with the rapid development of electronic products, the circuit of ultrasonic rangefinder controlled by SCM (single chip microcontroller) becomes more simple and the signal processing turns more convenient. The paper designs a high precision ultrasonic rangefinder, selecting a SCM as the controller. The SCM chooses the production-HT46F49E of Taiwan Holtek Semiconductor Inc, which has high reliability, low cost, low failure rate, etc. The chip has a built-in A/D converter, which can reduce the number of the peripheral devices.Ultrasonic ranging technology bases on the principle that ultrasonic wave can reflect when it meets obstacles. According to testing the transmission time, the ultrasonic rangefinder may acquire the distance. Ultrasonic attenuation in the air is severe, the measurement signal is unstable and measurement error is big for long distance; while measuring short distance, the echo signal is influenced by sending signal, which will produce larger measurement blind area.The paper analyzes related factors that influence ultrasonic rangefinder range and measuring precision. The launch of the ultrasonic rangefinder increases the sending signal power to compensate for ultrasonic attenuation in the air. The receiver circuits magnify the echo by two stage amplifier firstly, then using two-order active low pass filter filters high frequency signal. Through the voltage doubling shaping circuit and comparing circuit, the echo becomes better to trigger the SCM. In addition, the rangefinder also increases the temperature measurement circuit to compensate the measurement measuring errors for temperature. The results show that the measurement range of the rangefinder is moderate, who has higher precision and reliability. The measurement range is 4cm～300cm. The measurement error is less than lcm for short distance while it is over 1 cm for long distance. This paper which is based on the measuring results analyses other factors that cause measurement errors, and put forward improving methods finally.