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                          AMBULANCE SIREN CIRCUIT

Introduction:

This circuit sounds a siren like an ambulance siren.This circuit is different from an ambulance siren circuit. This circuit uses transistors instead of  555 timer IC which allows economical and easy to tailor a network. 

Circuit Diagram:

 Components Used:

1. Six npn transistors : Q1, Q2, Q3, Q4, Q5 and Q6
2. Resistors : R1 = 18k, R2 = 1.2M, R3 = 1.2M, R4 = 10k, R5 = 1.2M, R6 = 10k, R7 = 18k,         R8 = 12k, R9 = 100k, R10 = 10k and R11 = 11k.
3. Capacitors : C1= 10uf, C2= 1uf, C3= 1uf, C4= 1uf, C5= 0.04uf and C6= 0.04uf.
4. A battery for supply voltage of 9Volt.
5. A speaker

Working : 

The circuit can be divided into three main parts. They are the low frequency production, production of high frequency and the amplifier.  The low frequency production part includes Q1, Q2, R2, R3,C2, C3. This will produce low frequency out and to extend the Q3. Before we sent with high frequency of origin from Q4, Q5, R8, R9, C5, C6 signal is included, then the output will come out to the leg E of the Q5 and then be expanded with Q6 to drive the speakers.The resistor R11 will help to prtevent the speaker damage.
 

               CANARY CHIRP GENERATOR

Introduction:

This is an electronic alarm circuit that imitates the chirping of a canary. This circuit will generate a sound like bird's chirp. The transformer used here is a small audio transformer. The primary is center tapped with an impedance of 1Kohms at 1Khz. The secondary has an impedance of 8 ohm.

Circuit Diagram: 

Components Used:

1. Resistors:  R1= 4.7k , R2 = 47k 
2. Capacitors: C1 = 100uf , C2 = 100uf , C3 = 10nf , C4 = 22nf 
3. A npn transistor. 
4. A center tapped transformer. 
5. A speaker of 8 ohm. 
6. A battery for supply voltage of 9Volt. 
7. A push button switch.

 Working:

The inculsion of R1 and C1 give the oscillator its characteristic “chirp”. As the 100uf capacitor charges through the 4.7k resistor, R1 the bias for the transistor is cut off. This cause the oscilloscope to stop  and the capacitor discharges through the base emitter circuit of the transistor  and the oscilloscope start again. Altering these components alters the frequency of the chirp. The chirp is also voltage dependent. When the push button switch is operated the 100uf capacitor is charged. when its released the oscillation decays and the chirp becomes faster. 

      CONTACTLESS TELEPHONE RINGER CIRCUIT

Introduction: 

The contact less telephone ringer circuit can produce a ring as well as a visual indication when a call comes. The main advantage of this is that since there is no direct contact  between the phone line and the circuit there is no chance for a loading or disturbance in the telephone line.

 Circuit Diagram:

  Components Used:

1. Resistors: R1= 500k , R2 = 12k , R3 = 2.2k , R4 = 2.2k 
2. Capacitors: C1 = 1uf , C2 = 0.1uf 
3. An Inductor L1. 
4. Q1, Q3, Q4 are the npn transistors, Q2 is the pnp transistor. 
5. A piezo buzzer 
6. Battery for supply voltage of 9Volt. 
7. A SPST switch.

Working:

When the telephone ring 60Hz AC signal is generated which produces a proportional magnetic field around the telephone lines. These magnetic field will be picked up by the coil L1 due to electromagnetic induction. A proportional voltage is developed across L1 and it will bias transistor Q1 to ON. This results in the conduction of transistors Q2, Q3 and Q4. The buzzer will ring and the LED will glow. The switch S1 acts as an ON/OFF switch.

                  DING DONG SOUND GENERATOR

Introduction:

The ding dong sound generator circuit mainly consists of two 555 timer ICs. The first timer IC is operated in astable mode and the frequency of the second is modulated by the first timer. For that, output pin of the first IC is connected to the 5th pin i.e., the control pin of the second IC. The first timer IC is operated at a frequency of 1Hz. Astable mode is a free running mode of the 555 timer IC can be operated at required frequency by tuning the RC circuit. In astable mode no external triggering is required. This has no stable state.

Circuit Diagram:

 Components Used:

1. Two 555 timer ICs 
2. Resistors: R1 = 2.2k  , R3 = 2.2k 
3. Variable Resistors: R2 = 47k , R4 = 100k 
4. Capacitors: C1 = 47uf , C2 = 0.01uf , C3 = 0.1uf , C4 = 1uf/15V 
5. A speaker of 8 ohm 
6. Ground

Working:

When the power is ON, the circuit is operated in astable mode. As the voltage is applied to the timer the capacitor statrs charging through the resistors R1 and R3.When it reaches 2/3 of Vcc, it is detected by the sixth pin and the seventh pin is connected to the ground. The capacitor starts discharging through the R2 resistor. When voltage of 1/3 of Vcc is detected it again starts charging thus this process continuously produces the pulse of frequency 1Hz. This is applied to the second timer through its control pin. Thus the frequency of the second timer is modulated and is applied to the speaker through a capacitor. The external RC circuit decides the time delay with which the waveform should be produced. Hence one can hear the ding dong sound produced.

 Applications:

1. The circuit can be used as door bell by connecting the supply to a switch. 
2. With some modifications it can be used to produce different sounds.

                    POLICE SIREN USING 555 TIMER

Introduction:

This circuit produces a sound similar to the police siren. The two 555 timer acts as an atable multivibrator. The 555 timer IC is an integrated circuit used in a variety of timer, pule generation and ocillator applications. The 555 timer can be used to provide time delays as an oscillator and a a flip flop element. In the beginning 555 is coupled like a low frequency oscillator so to command the voltage at the second 555 IC at pin 5 which is a control pin. The shifting of the voltage on pin 5 is the root of the second oscillator frequency to get up and down.

Circuit Diagram: 

Components Used:

1. Two 555 timer ICs 
2. Resistors: R1 = 68k, R2 = 68k, R3 = 8.2k, R4 = 8.2k and R5 = 10k 
3. Capacitors: C1 = 10uf, C2 = 10uf, C3 = 100nf, C4 = 1uf 
4. A diode 
5. A supply voltage of 5Volt 
6. A speaker

 Working :

The police siren circuit explained here worked on NE555 timer IC. The circuit is build with the help of two NE555 IC which is the basic block of this circuit. Both the timer IC in this circuit is connected like a astable multivibrator. Although both the IC in the circuit work at two dissimilar frequencies. IC1 is astable multivibrator of slow frequency, works on frequency of 20Hz and having 50% of duty cycle while IC2 is a fast astable multivibrator works on frequency of 600Hz. IC1 output is then serve to IC2 at the control pins. With the help of this arrangement IC2 output frequency will be modulated with the IC1 output frequency. The circuit works on the DC supply between a range of 6V to 15V.

               PWM LAMP DIMMER USING 555 TIMER

Introduction:

In this circuit PWM is used to dim the intensity of the LED light. Here, the DC source is connected to NE555 timer IC. The PWM signal always depends on the duty cycle, so we can vary the duty cycle through NE555 timer IC. If we vary the duty cycle we can generate the pulse with various width. So we use timer to generate the PWM to dimmer the lamp or to increase the brightness of the lamp.

Circuit Diagram: 

Components Used:

1. A 555 timer IC 
2. Two npn transistors 
3. Resistors: R1= 1k, R2 = 1k, R3 = 50k, R4 = 1k 
4. Capacitors: C1 = 0.01uf, C2 = 0.01uf 
5. A diode 
6. A lamp 
7. Supply voltage of 12Volt 
8. Ground

Working :

NE555 timer IC which is wired as an astable multivibrator operating at 2.8kHz is the main part of this circuit. Resistors R1, R2, potentiometer R3 and capacitor C1 are the timing components. Duty cycle of the IC's output can be adjusted using the potentiometer R3. Higher the duty cycle means higher the lamp brightness and lower the duty cycle means lower the lamp brightness. Diode D1 by-passes the lower half of the potentiometer R3 during the charging cycle of the astable multivibrator. This is done in order to keep the output frequency constant irrespective of the duty cycle. The two npn transistors forms a darlington driver stage for the 12V lamp. Resistor R4 limits the base current of transistor Q1.
 

    REFRIGERATOR DOOR DETECTOR ALARM

Introduction:

Not properly closing the door of the refrigerator will consume more electricity. The refrigerator door detector alarm circuit detects the light of the lamp in the fridge and alert with a buzzer. The buzzer will beep whenever the door of the refrigerator is opened for an extended period of time.

Circuit Diagram:

 Components Used:

1. A photoresistor 
2. A npn transistor
3. Resistors: R1 = 5k, R2 = 1k
4. Potentiometer: VR1 = 50k
5. A buzzer
6. A battery of 9Volt

Working:

When we close the door the refrigerator the light bulb in the refrigerator gets off. The resistance of potentiometer gets very high which causes a low voltage across both R1 and VR1. This voltage is not enough to bias the transistor and makes the transistor working, thus no current flows to to the buzzer and therefore no sound is produced.
    When we open the door of the refrigerator the light bulb will glow which causes the resistance of potentiometer to reduce, voltage across R1 and VR1 rises until makes the transistor working. The current now flows to the buzzer and makes the buzzer to work and produces an alarm sound at the output.

                         RINGING PHONE LIGHT FLASHER

Introduction:

This circuit is designed to glow or to turn a alarm when the phone rings. Using this circuit nuissance of telephone ring at night can be avoided.

Circuit Diagram:

 Components Used:

1. A npn transistor 
2. An optoisolator
3. An SPDT relay
4. Resistors: R1 = 10k, R2 = 100k and R3 = 1k
5. Capacitor C1= 0.47uf
6. Diodes: D1, D2, D3 and D4 
7. A power supply of 5Volt

Working:

When the telephone rings the line voltage rises to 72Volts. At this time the LED in the opto-coupler glows and the transistor conducts. Due to this the transistor conducts. This makes the relay ON. The load connected to the relay whether bulb or bell turns ON.

              

                       SIMPLE BATTERY CHARGER

 Introduction:

Here is the circuit diagram of a simple and straight forward 12 V battery charger circuit with diagram. This circuit can be used to charge all type of 12V rechargeable batteries including car batteries.

Circuit Diagram: 

Components Used:

1. A transformer 
2. Two diodes 
3. Capacitor of 2200uf/25V 
4. Ammeter 
5. A battery of 10Volt

 Working:

The circuit is nothing but a 12V DC power supply with an ammeter for monitoring the charging current. The two diodes forms a centre tapped full wave rectifier. The capacitor filters the rectifier output to produce a clean 12V output. At initial stages of charging the ammeter will read about 1 to 3 amperes. As the battery is slowly charged the current will slowly decreases. When the battery is fully charged the ammeter reading will be zero.

                      TELEPHONE-OFF HOOK INDICATOR

Introduction:

The circuit depicted here can be used as an indicator when the telephone receiver is off-hook. The circuit can be in corporated with old telephones that does not have such an indicator.

Circuit Diagram:

 Components Used:

1. A pnp and anpn transistor. 
2. Resistors: R1 = 100ohm, R2 = 680k, R3 = 3.3M, R4 = 3.3M 
3. Capacitor C1= 0.1uf 
4. A LED 
5. A battery of 3V

Working :

The circuit uses a complementary darling to pair using Q1 and Q2  to sense whether the receiver is off hook and glows a LED to show the condition. The LED will glow when the circuit is not connected to the telephone line.

                

                 ZERO DEGREE CELCIUS ALARM CIRCUIT

Introduction:

Basically this zero degree celcius alarm circuit used a thermistor to sense the temperature. This circuit uses a buzzer that will produce an alarm whenever the temperature falls below zero degree.

 Circuit Diagram:

 Components Used :

1. Op-amp LM7215 IC 
2. A npn transistor 
3. Resistors: R1 = 720k, R2 = 1M,  R4= 1k, R5 = 1k 
4. Capacitor C1= 0.1uf 
5. Thermistor R4 = 1k 
6. A buzzer

 Working:

Basically the zero degree celcius detector used a thermistor to sense the temperature. This circuit uses a buzzer which will produce an alarm whenever the temperature falls to zero degree. The op-am here used is to compare the reference voltage and voltage from the thermistor network. Reference voltage is given to the non-inverting terminal of the op-amp and the thermistor network voltage is applied to the inverting terminal of the op-amp. When the temperature becomes less than zero degree celcius, the non-inverting input gets larger than the input at the inverting terminal and the op-amp output becomes high. This makes the transistor ON and produces an alarm.