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INTRODUCTION
This is a very interesting project with many practical applications in security and alarm systems for homes, shops and cars. It consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered by the circuit the circuit’s fine balance is disturbed and the alarm is triggered. The circuit is very sensitive and can be adjusted to reset itself automatically or to stay triggered till it is reset manually after an alarm.
Technical Specifications – Characteristics
Working voltage: 12V DC
Current: 30 mA
WORKING PRINCIPLE
As it has already been stated the circuit consists of an ultrasonic transmitter and a receiver both of which work at the same frequency. They use ultrasonic piezoelectric transducers as output and input devices respectively and their frequency of operation is determined by the particular devices in use.
The transmitter is built around two NAND gates of the four found in IC3 which are used here wired as inverters and in the particular circuit they form a multivibrator the output of which drives the transducer. The trimmer P2 adjusts the output frequency of the transmitter and for greater efficiency it should be made the same as the frequency of resonance of the transducers in use. The receiver similarly uses a transducer to receive the signals that are reflected back to it the output of which is amplified by the transistor TR3, and IC1 which is a 741 op-amp. The output of IC1 is taken to the non inverting input of IC2 the amplification factor of which is adjusted by means of P1. The circuit is adjusted in such a way as to stay in balance as long the same as the output frequency of the transmitter. If there is some movement in the area covered by the ultrasonic emission the signal
that is reflected back to the receiver becomes distorted and the circuit is thrown out of balance. The output of IC2 changes abruptly and the Schmitt trigger circuit which is built around the remaining two gates in IC3 is triggered. This drives the output transistors TR1,2 which in turn give a signal to the alarm system or if there is a relay connected to the circuit, in series with the collector of TR1, it becomes activated. The circuit works from 9-12 VDC and can be used with batteries or a power supply.
CIRCUIT DIAGRAM CONSTRUCTION
First of all let us consider a few basics in building electronic circuits on a printed circuit board. The board is made of a thin insulating material clad with a thin layer of conductive copper that is shaped in such a way as to form the necessary conductors between the various components of the circuit. The use of a properly designed printed circuit board is very desirable as it speeds construction up considerably and reduces the possibility of making errors. Smart Kit boards also come pre-drilled and with the outline of the components and their identification printed on the component side to make construction easier. Soldering the components to the board is the only way to build our circuit and from the way we do it depends greatly your success or failure. This work is not very difficult and if we stick to a few rules we should have no problems. The soldering iron that we use must be light and its power should not exceed the 25 Watts. The tip should be fine and must be kept clean at all times. For this purpose come very handy specially made sponges that are kept wet and from time to time we can wipe the hot tip on them to remove all the residues that tend to accumulate on it. There are many different types of solder in the market and we should choose a good quality one that contains the necessary flux in its core, to assure a perfect joint every time. We DO NOT use soldering flux apart from that which is already included in our solder.
Ultrasonic Circuits
INTRODUCTION
This is a very interesting project with many practical applications in security and alarm systems for homes, shops and cars. It consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered by the circuit the circuit’s fine balance is disturbed and the alarm is triggered. The circuit is very sensitive and can be adjusted to reset itself automatically or to stay triggered till it is reset manually after an alarm.
Technical Specifications – Characteristics
Working voltage: 12V DC
Current: 30 mA
WORKING PRINCIPLE
As it has already been stated the circuit consists of an ultrasonic transmitter and a receiver both of which work at the same frequency. They use ultrasonic piezoelectric transducers as output and input devices respectively and their frequency of operation is determined by the particular devices in use.
The transmitter is built around two NAND gates of the four found in IC3 which are used here wired as inverters and in the particular circuit they form a multivibrator the output of which drives the transducer. The trimmer P2 adjusts the output frequency of the transmitter and for greater efficiency it should be made the same as the frequency of resonance of the transducers in use. The receiver similarly uses a transducer to receive the signals that are reflected back to it the output of which is amplified by the transistor TR3, and IC1 which is a 741 op-amp. The output of IC1 is taken to the non inverting input of IC2 the amplification factor of which is adjusted by means of P1. The circuit is adjusted in such a way as to stay in balance as long the same as the output frequency of the transmitter. If there is some movement in the area covered by the ultrasonic emission the signal
that is reflected back to the receiver becomes distorted and the circuit is thrown out of balance. The output of IC2 changes abruptly and the Schmitt trigger circuit which is built around the remaining two gates in IC3 is triggered. This drives the output transistors TR1,2 which in turn give a signal to the alarm system or if there is a relay connected to the circuit, in series with the collector of TR1, it becomes activated. The circuit works from 9-12 VDC and can be used with batteries or a power supply.
CIRCUIT DIAGRAM CONSTRUCTION
First of all let us consider a few basics in building electronic circuits on a printed circuit board. The board is made of a thin insulating material clad with a thin layer of conductive copper that is shaped in such a way as to form the necessary conductors between the various components of the circuit. The use of a properly designed printed circuit board is very desirable as it speeds construction up considerably and reduces the possibility of making errors. Smart Kit boards also come pre-drilled and with the outline of the components and their identification printed on the component side to make construction easier. Soldering the components to the board is the only way to build our circuit and from the way we do it depends greatly your success or failure. This work is not very difficult and if we stick to a few rules we should have no problems. The soldering iron that we use must be light and its power should not exceed the 25 Watts. The tip should be fine and must be kept clean at all times. For this purpose come very handy specially made sponges that are kept wet and from time to time we can wipe the hot tip on them to remove all the residues that tend to accumulate on it. There are many different types of solder in the market and we should choose a good quality one that contains the necessary flux in its core, to assure a perfect joint every time. We DO NOT use soldering flux apart from that which is already included in our solder.
