MOSQUITO REPELLENT

This circuit is based on the popular timer IC 555. This is a unique circuit that sends the mosquitoes flying away from your room. In this circuit, the IC 555 works as an oscillator that outputs a frequency range of minimum 200Hz to a maximum frequency range of 62 KHz. The output frequency can be adjusted by the preset R-2 connected in the circuit. A high quality speaker should be used with this circuit.

PARTS LIST::::
1/ IC 555
2/ Resistance : 220E, 1ME, Control- 5K
3/ Capacitor :0.005, 0.1, 100MF/10V, Loud speaker.

CHIRIPING SOUND (BIRD
SOUND) PRODUCING CIRCUIT
Many circuits can be designed to produce the sound of chiriping birds. Such circuits are used in the door bells and many toys. This circuit provides very interesting sound.

Two timer IC 555 are used in the circuit given here. Both the IC s are used here, in the astable mode. Here, the output is not taken from the output pin no.3 of the IC but triangular waveform is received from the junction of the pin no. 2 & 6of the IC. This triangular waveform is given to the control voltage pin no.5 of the IC2 through a resistance R3. Output received from the pin no.3 of the IC2 is given to the speaker through the capacitor C4. The circuit is operated at 6V DC supply.

Automatic time indicator for the Telephone

As, you already know, the telephone calls are charged on the basis of the time duration for which the call has been made. If the call is continued after the standard time is over, then your calling time will be extended and the charges will be added up accordingly. It is very difficult to keep an eye on the time elapsed while you are busy in talking on the phone. This novel circuit does just this for you while you are talking on the phone. The circuit gives out a warning signal after 2.5 minutes of starting the call.
The On/Off touch plates are made from the conducting silver paper strips and fixed in a suitable position on the cabinet.

Automobile Flasher
Electromechanical methods are still used switching the blinkers in the automobiles. Electronic automobile flashers are made by using transistors. In the circuit given here an IC has been used for the same purpose. The circuit is built around the popular timer IC 555 which is used in the as table mode. This is a free running multi vibrator. Here, the output pin no 3 of the IC 555 is connected with the base of the transistor T1( AD149 ). This transistor works as an electronic switch. The panel Leds connected on the dashboard indicate the working of the flasher bulbs. Rate of the flashing of the bulbs is kept at 95/min. This rate can be changed by changing the value of the capacitor C1. When the value of this capacitor is increased then the rate of flashing becomes faster. Transistor T1 ( AD149 ) is a power transistor and it is necessary to mount it on a heat sink. The LED indicates should be mounted at a convenient position on the dash board.

Automatic street light controller
This street light controller circuit is designed around a single IC timer 555. This IC has been used in it’s bi-stable mode in the circuit. Two LDRs are also used in this circuit to differentiate between the day light and the darkness of the light. During the day time this bi-stable circuit remains reset by the LDR-2 while in the night time this bi-stable is set by the LDR-1. The output from the timer IC is given to the base of transistor T-2 which drives the relay in turn. Street light connections are given from the N/O contacts of the relay as shown in the figure. The number of lights which can be connected in parallel to this circuit depends directly upon the load rating of the relay contacts.

Relay on/off Time Adjuster Circuit

This circuit is built around the popular timer IC 555. This circuit is designed to adjust both the on off times of the relay.

Here, the IC 555 has been used as an astable multivibrator. Diode D1 and D2 and two preset controls VR1 and VR2 have been used to get separate On and Off timings for the relay. By using this controls VR1 and VR2 the On and off timings of the relay can be adjusted independently.
Time period of the On and Off time to relay can be adjusted from 1 second to about 90 seconds by using the given values of VR1, VR2 and the capacitor C1. Take care to use a new IC for this circuit because a used IC may not perfom perfectly. Similarly, the Capacitor C1 should also be from a good and reputed manufacturer such as Keltron, Uptron or Phillips.

Simple Siren
There can be many siren circuits based on the IC 555. These circuits can be operated from 5V to 17V supply.

The circuit given here gives out the tone of a common siren. IC 555 is used in the circuit as an astable mutivibrator. The siren tone can be adjusted by preset VR1(10K). The capacitor used at pin no.3 of the IC, determines the shape of the outform waveform. Sound is received by giving the output to the speaker. If this output signal is amplified by a high power amplifier then a very loud sound can be received from this circuit.

Parts list::::::

Resistance :1K, PRESET 10KCapacitor : 10KPfx2, 10MF, 10V, 100MF, 10V, Loue speaker 8E.