Introduction to Ultrasonic Distance Meter
The project Ultrasonic Distance Meter is a very interesting and useful project for many industrial applications. In this project we have used the ultrasonic waves to measure the distance in between two points. The basic principal is based on the speed of ultrasonic waves in open air. We have used a microcontroller AT89S51 to transmit and receive ultrasonic waves through 40 KHz ultrasonic receiver and transmitters. By measuring the time required to travel the unknown distance by ultrasonic waves in air we can find out the distance between two points. The distance measured is displayed on a LCD display. The transmission & reception of ultrasonic waves is very complex in nature so it needs very sophisticated techniques to process these waves. We have used a very complex structure of amplifier and filters for this purpose. The speed of ultrasonic waves is dependent on temperature. So before using ultrasonic waves for any measurement we need to calibrate the speed of ultrasonic waves in current atmospheric temperature. For this purpose we have implemented a special algorithm to calibrate the speed of ultrasonic waves through a known distance of 100 Cm. There are numerous applications of ultrasonic waves in instrumentation and control. These applications include measurement of distance, speed, flow etc. Ultrasonic also find many application in medical instrumentation.
FUNCTIONAL BLOCK DIAGRAM
• Transducer pair (MuRata, MA40S/R).
• 12MHz Crystal.
• Low power operational amplifiers (LM741).
• Shottky Barrier Diodes (BYV10).
• Low power operational amplifiers (LM358).
• NAND Gates (4011B).
• Inverter (4069UB).
• Transistor (2SA1015, 2SA1815).
• Seven Segment Displays (common anode).
• Several resistors.
• Several capacitors.
THE TRANSMITTER PART
Here in this project we use 40 kHz transmitter. This 40 kHz frequency is generated by the microcontroller. We use one oscillation circuit + time circuit to control the sending-out time of the ultrasonic pulse. The circuit is the same as the ultrasonic range meter. The oscillation frequency is the same.
The inverter is used for the drive of the ultrasonic sensor. The two inverters are connected in parallel because of the transmission electric power increases. The phase with the voltage to apply to the positive terminal and the negative terminal of the sensor has been 180degrees shifted. Because it is cutting the direct current with the capacitor, about twice of voltage of the inverter output are applied to the sensor. The power supply voltage of this drive circuit is +9V. It is converting voltage with the transistor to make control at the operating voltage of PIC (+5V). Because C-MOS inverters are used, it is possible to do ON/OFF at high speed comparatively.
This IC is the IC of the CMOS which the six inverters are housed in. At the transmitter circuit, it is used for the drive circuit of the ultrasonic sensor.
THE RECEIVER PART
SIGNAL AMPLIFICATION CIRCUIT
The ultrasonic signal which was received with the reception sensor is amplified by 1000 times (60dB) of voltage with the operational amplifier with two stages. It is 100 times at the first stage (40dB) and 10 times (20dB) at the next stage. Generally, the positive and the negative power supply are used for the operational amplifier. The circuit this time works with the single power supply of +9 V. Therefore, for the positive input of the operational amplifiers, the half of the power supply voltage is applied as the bias voltage. Then the alternating current signal can be amplified on 4.5V central voltage. When using the operational amplifier with the negative feedback, the voltage of the positive input terminal and the voltage of the negative input terminal become equal approximately. This is called virtual grounding. So, by this bias voltage, the side of the...
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