This device calculates the distance based on the speed of sound at 25o C ambient temperature and shows it on a 7-segment display. Using it, you can measure distance up to 2.5 meter. For this particular application, the required components are AT89C2051 Microcontroller, two 40KHZ ultrasonic transducers (one each for transmitter and receiver), current buffer ULN2003, operational amplifier LM324, inverter CD4049, four 7-segment displays, five transistors and some discreet components.
In this project, you excite the ultrasonic transmitter unit with a 40KHZ pulse burst and expect as echo from the object whose distance you want to measure. Fig. 1.2. shows the transmitted burst, which lasts for a period of approximately 0.5 ms. It travels to the object in the air and the echo signal is picked up by another ultrasonic transducer unit (receiver), also a 40 KHZ pre-tuned unit. The received signal, which is very weak, is amplified several times in the receiver circuit and appears somewhat as shows in Fig.1.2 when seen on a CRO.Weak echoes also occur due to the signals being directly received through the side lobes. These are ignored as the real echo receive alone would give the correct distance
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