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Listening Bug

Listening Bug

How great, if you are able to listen the people sitting in the adjoining room. This project provides an effective way to this imagination.

This is a very simple and inexpensive circuit uses an operational amplifier IC 741 (IC1) and push-pull amplifier using transistors for amplification of a signal.

 

Refer PDF for more information:


Liquid Level Indicator

Liquid Level Indicator

The name of the project itself suggests its application. It can be used for level control in hydroculture project. Also for kitchen purpose like detecting the level of water in washing machine. The main feature of this circuit is that it shows each level in meaningful English letters. It displays letter ‘E’ for Empty, ’L’ for Low, ’H’ for Half, ’A’ for Above Average and ‘F’ for Full Tank. The sensors for each level are immersed in tank. Their other ends get interconnected through four NOR gates, which uses IC1. The output is then given to IC2, which is BCD to seven- segment display driver IC. The level of fluid is indicated on 7- segment display.

Refer PDF for more information:


Two Way Intercom

Two Way Intercom

This inexpensive two way intercom provides a simple way by which we can communicate in two ways i.e. send a signal as well as receive a signal. The circuit is build around timer IC555 (IC1) and low power audio amplifier IC386 (IC2). The circuit is designed in two parts. Here the circuit diagram of one part is shown in figure. The output of one unit is given to the input of other unit. The two parts are connected by three way wire connection points. These points are denoted by 'S' for supply, 'O' for output and 'G' for ground.

 

About the Circuit:

 

When switch 'S1' is pressed, IC1 gets triggered. Hence IC1, which is connected in astable mode, acts as a tone generator or oscillator. These oscillations generated at output pin3 are given to bypass input pin7 of IC2. The sound signals generated due to communication are received by condenser mic connected at audio input pin3 of IC2. These signals are amplified by audio amplifier IC2 and the amplified output generated at pin5 is given to Loudspeaker through coupling capacitor C1. We can mute the unit by pressing switch S2. The components mentioned in the part list are only for one side. The other side of the unit uses the same components. Hence twice the components mentioned in the part list should be used except power supply. Three Core shielded wire of about 4-10 meters can be used for connections between two units.

 

Note on IC386:

 

As stated earlier, IC386 is a low power audio amplifier IC, which is very inexpensive and widely used. Some of the important features of this IC are:

 

  • Minimum external parts
  • Low distortion
  • Wide supply voltage range

 

Power supply:

 

The circuit requires a regulated DC power supply of 9V. For this, the power supply design is shown in figure. The assembled module of power supply is to be kept inside one intercom hand set.


Infrared Remote Switch

Infrared Remote Switch

The circuit described here can be used for any simple on/off function such as controlling a lamp or fan. The major advantage is that this circuit is absolutely free from ambient light interference and provides controlled range of about 10 mt without the use of any focusing lens. Transmitter and receiver circuits are described below:

Transmitter section consists of a power supply, an oscillator and an output stage. The circuit diagram for transmitter is shown in fig. IC1 is wired as an astable multivibrator with a center frequency of about 26KHz. When switch S1 is pressed, the circuit gets energized, output of IC1 is a square wave. The infrared LED connected at it’s output transmit IR beams modulated at the same frequency. The oscillator frequency can be shifted slightly by adjusting preset VR1.

 

Receiver Circuit:

 

Receiver section comprises power supply an infrared detector module, time delay circuit with noise filter, bistable flip-flop and an output section.The IR signal from the transmitter is sensed by the sensor and output at pin 2 goes low. This in turn switches on transistor T1. Consequently, capacitor C8 starts charging through resistor R5. When voltage across capacitor C8 reaches about 3.5V, IC2 receives a clock pulse at pin 14 and its output at pin2 goes high. As a result T2 becomes on, whish energizes relay RL1. The output of IC2 is also used for lighting the LED D5 indicating the presence of a signal.

 

When ON signal is available output of sensor goes high and T1 is switched OFF. Now capacitor C8 starts discharging through R6 and voltage across it decreases to zero. When another signal arrives after about 300miliseconds capacitor C8 again charges through R5 and IC2 gets another clock pulse. But its reset through diode D4, the output at pin2 toggles.

 

If another pulse arrives from the transmitter before a delay of about 300ms, T1 again turns ON and voltage across C8 cannot fall below 1.5V i.e. maximum input voltage required to sense a logical low by IC2. Hence, the output of IC2 does not change. This feature prevents false triggering. R5, C8 network provides immunity against IR noise. IC3 is a regulator IC that provides a regulated voltage.

 

Protect your circuit:

 

High frequency produces a lot of harmonics act as a source sustained noise. To minimize this effect, the sensor should be covered with a dark red glass plate light from other sources like fluorescent lamps. IR candescent lamps and sunlight do not have any effect on the circuit.

 

Calibration:

 

If LED D5 does not glow, adjust preset VR1 till it glows. Gradually increase the distance and fine-tune the preset for maximum range.


Ultrasonic Radar

Ultrasonic Radar

This project brings you the latest application in the field of security systems. Also it can be used as a burglar alarm for homes etc. It consists of a set of ultrasonic transmitter and receiver transducers, which operate at the same frequency. When any object moves in the area covered by the circuit, the circuit’s fine balance is disturbed and the alarm is raised. The circuit is very sensitive and can be adjusted to reset itself autometically or to stay triggered till it is reset manually after an alarm.

 

About the Circuit:

 

The circuit of Ultrasonic Radar is shown in figure. Transmitter and Receiver uses 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 build 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 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 T3, and IC1, which is 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 as 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 build around the remaining two gates in IC3 is triggered. This drives the output transistor T1, T2, which in turn gives a signal to the alarm system. The circuit works from 9-12V DC and can be used with batteries or a power supply.

 

Calibration:


Trimmer P1 is set at its middle position. Turn then P2 slowly till the LED lights when you move your fingers slightly in front of the transducers. Adjust then P1 for maximum sensitivity. Connecting together pins 7 & 8 will make the circuit to stay triggered till it manually reset after an alarm. This can be very useful if you want to know that there was an attempt to enter in the place, which are protected by the radar.


Two In One Electronic Game

Two In One Electronic Game

It incorporates electronic Roulette wheel and indoor cricket.Here is a simple circuit wired around popular timer IC as IC1 and decade counter IC2. As the name implies it incorporates two fascinate games Electronic Roulette Wheel (gambling) and indoor cricket.

 

About the Circuit:

 

When S1 in position as shown in the figure, capacitor C1 charges through R1, S2 discharges the capacitor and a signal with decaying time period is produced at the output of IC1. This is seen as a running effect of light at the output of IC2. After a few seconds only one LED glows and the running effect vanishes. If the last LED that a glow is the selected one, the player wins otherwise he losses.

 

Indoor cricket is still more interesting. Nowadays children do not get enough space to play games like cricket. To play indoor cricket, change the position of S1. One particular LED glows, indicating the status of the player. A score chart is suggested here with reference to LED numbers but it can be easily changed.In this case, IC1 produces a steady output. The values of R2 and C2 may be changed for quick effect and high frequency respectively.

 

A unique feature of this circuit is that it can be operated with any voltage between +6V and +12V. Thus a voltage regulator is not required. IC1 is wired to produce a frequency of 50Hz and IC2 is a decade/counter divider.The value of R6 should be increased if the supply voltage increased.


Temperature Switch

Temperature Switch

The circuit of temperature switch described here, autometically switches on a device when the temperature rises to about 60°C. It is a very simple circuit build around IC1, which is operated in monostable mode and temperature sensor diode D1. At temperature about 60°C, the sensor triggers IC1, which makes output of IC1 at high level and energises the relay. Also it becomes off as temperature goes below 60°C.

 

About the Circuit:

The circuit of Temperature Switch is shown in figure. Sensor Diode D1 in reverse bias is connected to trigger pin2 of IC1. At temperature below 60°C, the reverse resistance of D1 is very high, which keeps trigger pin2 of IC1 at a voltage greater than 1/3Vcc. Hence IC1 doesn’t get trigger, which gives low pulse at output pin3. As a result transistor T1 is in cut off state and relay remains off.

 

As soon as the temperature reaches to about 60°C, the reverse resistance of D1 drops to a very low value normally less than 1KW. In this case it is considered as forward bias. As a result voltage at pin2 goes below 1/3Vcc. Now IC1 gets triggered and output at pin3 goes to high level, which causes T1 to conduct. Relay connected to collector of T1 now becomes on. Also LED D4 glows which gives visual indication.

 

The sensitivity of the circuit is adjusted with the aid of P1. The circuit requires a DC power supply of 9V to 12V. Diode D3 is used as a rectifier diode whereas capacitor C4 is used for filtering.


Modern Traffic Light Signal

Modern Traffic Light Signal

The use of few ics makes it possible to control the big traffic in modern way in your city. The schematic arrangement for traffic light is shown in figure. It includes four set of poles having red, yellow, green and side-green lights at each pole. At a time, green signal for opposite poles p1-p3 and red signal for other two opposite poles p2-p4 on. When the green signal goes off, side-green signal glows for side way traffic. As the side-green signal of p1-p3 goes off, green signal of p2-p4 and red signal of p1-p3 becomes on.the circuit is designed using two-shift register ic3 and ic4, which consists of each eight outputs. It controls hold on time for each signal. Ic5, ic6 and ic7 are used as a buffer to isolate the output. Ic1 is used as a astable multivibrator to provide clock input to ic3 and ic4. Ic2 which is a or gate ic used to give data-in signal to ic3.

About the Circuit:

As stated in introduction ic3 which is a shift register has eight outputs. As we require 16 outputs for controlling the four set of poles two ics are used. Ic1 is used to give clock signal to ic3 and ic4 at pin 1 and 9 respectively as shown in circuit diagram. At every clock pulse generated by ic1 output goes on shifting. When power is on, ic2 provides data-in signal to ic3 at pin7. Ic3 starts shifting the output. The first three outputs are used for green signal, the fourth output for yellow signal. The next three output for side-green signal and the last output for side-yellow signal. As this is arrange for opposite two poles p1-p3, at the same time all the eight outputs are used as a red signal for other two opposite poles p2-p4. At the last output of ic3, ic4 receives data-in signal by connecting pin2 of ic3 to pin7 of ic4. Now ic4 starts shifting the output. Ninth to sixteenth outputs generated from ic4 are used same as above, but for other set of pole

 

The clock pulses generated by ic1 are indicated by led d49, whose frequency is set by preset p1. Whereas when ic2 gives the data-in signal to ic3, led d52 glows.

 

Calibration:

It should be noted that the clock signal and data-in signal are adjusted in proper way. When power is on at first clock pulse, ic3 gets the data-in signal, which is indicated by glowing of led d52. But the output starts at second clock pulse. When second clock pulse goes of led d52 must also be goes off, otherwise the circuit does not work properly. This is adjusted by preset p2.

 

Leds colour specification for four set of poles are as follows:


  • Pole-1: d37-red, d34-yellow, d35-green, d36-green right
  • Pole-2: d33-red, d38-yellow, d39-green, d40-green right
  • Pole-3: d45-red, d42-yellow, d43-green, d44-green right
  • Pole-4: d41-red, d46-yellow, d47-green, d48-green right

 

Power Supply:

 

The circuit requires a dc power supply of 12v. The 12v ac output from 12-0-12v transformer gets rectified by diodes d53/d54. Capacitor c10 filters the rectified signal. This rectified output is given to input of ic8, which is a 12v regulator ic. The final regulated output is applied to the circuit.

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