Ultrasonic waves are waves with frequencies above the frequency of the sound waves of more than 20 KHz. As it has been mentioned that the ultrasonic sensor consists of an ultrasonic transmitter circuit called ultrasonic transmitter and receiver circuit called a receiver. Ultrasonic signals generated will be emitted from the ultrasonic transmitter. When the signal on an obstacle, then the signal is reflected and received by the ultrasonic receiver. Signal received by the receiver circuit to be sent to the microcontroller circuit further processed to calculate the distance to objects in front of it (the field of reflection).
The working principle of ultrasonic sensors can be shown in the image below:
Working Principle Ultrasonic Sensor
The working principle of ultrasonic sensors is as follows:
- Ultrasonic signal emitted by the transmitter. The signal frequency above 20kHz, which is usually used to measure the distance of objects is 40kHz. The signal is raised by the circuit in ultrasonic transmitter.
- The transmitted signal will then propagate the signal / noise sound wave with a speed that ranges from 340 m / s. The signal will then be reflected and received by the receiver Ultrasonic parts.
- After the signal reached the ultrasonic receiver, then the signal is processed to calculate the distance. Distances are calculated based on the formula:
S = 340.t / 2
where S is the distance between the ultrasonic sensor with reflective fields, and t is the time difference between transmitting ultrasonic waves to be accepted back by the ultrasonic receiver section.
a. The ultrasonic transmitter (Transmitter)
The ultrasonic transmitter that emits a series of sinusoidal signal frequency above 20 KHz using an ultrasonic transmitter transducer
- The transmitter circuit Ultrasonic Wave
The working principle of the ultrasonic wave transmitter circuit adlah as follows:
- 40 kHz signal generated by the microcontroller.
- The signal is passed to a resistor of 3kOhm to safety when the signal is refracted forward a series of diodes and transistors.
- Then the signal is fed to a current amplifier circuit which is a combination of 2 pieces 2 pieces of transistors and diodes.
- When the signal from the input logic high (+5 V) then the current will pass through the diode D1 (D1 on), then the current will bias transistor T1, so the current will flow in large kolektotr T1 will fit on the strengthening of the transistor.
- When the signal from the input logic high (0V) then the current will pass through the diode D2 (D2 on), then the current will bias the transistor T2, so the current will flow in large kolektotr T2 will fit on the strengthening of the transistor.
- Resistors R4 and R6 serve to divide tengangan to 2.5 V. Ultrasonic transmitter so it will accept the voltage back – back with Vpeak-peak is 5V (+2.5 V up to -2.5 V).
b. Ultrasonic receiver (Receiver)
Ultrasonic receiver will receive the signal emitted by the ultrasonic transmitter ultrasonic frequencies corresponding to the characteristic. The received signal will go through frequency filtering process by using a series of band pass filter (bandpass filter), with a frequency value that is passed has been determined. Then the output signal will be amplified and passed to a comparator circuit (comparator) with a reference voltage amplifier output voltage is determined by the distance between the sensor when the mini vehicles with bulkhead / barrier wall to reach the minimum distance to the turn direction. Comparator output can be considered under these conditions is high (logic ‘1 ‘) while the longer distance is low (logic ‘0’). Binary logics are then forwarded to the controlling circuit (microcontroller).
Receiver circuit Ultrasonic Wave
The working principle of ultrasonic wave transmitter circuit are as follows:
- First – all the received signal will be amplified by the first amplifier circuit transistor Q2.
- The signal will then be filtered using High pass filter at frequencies> 40kHz by a series of transistor Q1.
- After the signal is amplified and filtered, then the signal will be rectified by the diodes D1 and D2 series.
- Then the signal through a low pass filter circuit filter at a frequency of <40kHz through a series of filters C4 and R4.
- After that the signal will go through the Op-Amp comparator U3.
- So when there is an ultrasonic signal into the circuit, then the comparator will issue a logic low (0V) which will then be processed by the microcontroller to calculate the distance.