Speaker to Microphone Convertor
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Battery Charger Circuit
Description :
A simple battery charger based on SCR is shown here.Here the SCR rectifies the AC mains voltage to charge the battery.When the battery connected to the charger gets discharged the battery voltage gets dropped.This inhibits the forward biasing voltage from reaching the base of the transistor Q1 through R4 and D2.This switches off the transistor.When the transistor is turned OFF,the gate of SCR (H1) gets the triggering voltage via R1 & D3.This makes the SCR to conduct and it starts to rectify the AC input voltage.The rectified voltage is given to the battery through the resistor R6(5W).This starts charging of the battery.
When the battery is completely charged the base of Q1 gets the forward bias signal through the voltage divider circuit made of R3,R4,R5 and D2.This turns the transistor ON.When the Q1 is turned ON the trigger voltage at the gate of SCR is cut off and the SCR is turned OFF.In this condition a very small amount of charge reaches the battery via R2 and D4 for trickle charging.Since the charging voltage is only half wave rectified ,this type of charger is suitable only for slow charging.For fast charging full wave rectified charging voltage is needed.
When the battery is completely charged the base of Q1 gets the forward bias signal through the voltage divider circuit made of R3,R4,R5 and D2.This turns the transistor ON.When the Q1 is turned ON the trigger voltage at the gate of SCR is cut off and the SCR is turned OFF.In this condition a very small amount of charge reaches the battery via R2 and D4 for trickle charging.Since the charging voltage is only half wave rectified ,this type of charger is suitable only for slow charging.For fast charging full wave rectified charging voltage is needed.
Circuit diagram with Parts list :
Notes :
- Assemble the circuit on a good quality PCB or common board.
- The transformer T1 can be 230V primary, 18V /3A secondary step down transformer.
- The voltage of the battery at which the charging should stop can be set by the POT R4.
- The battery can be connected to the charger circuit by using crocodile clips.
Speaker to Microphone Convertor
Description :
This circuit is a simple approach for converting a loud speaker into a microphone. When the sound waves fall on the diaphragm of a speaker, there will be fluctuations in the coil and there will be a small proportional induced voltage. Usually this induced voltage is very low in magnitude and useless. Here in the circuit the low voltage is amplified using transistors to produce a reasonable output. The transistor Q1 is wired in common base mode and produces the required voltage gain. The transistor Q2 is wired as an emitter follower to produce enough current gain. The voice quality of this circuit will not be as much as a conventional microphone but quite reasonable quality can be obtained. To set up the circuit, keep the preset R2 at around 10 Ohms and connect the battery. Now adjust R2 to obtain the optimum sound quality.
Circuit diagram with Parts list :
Notes :
- Assemble the circuit on a general purpose PCB.
- Power the circuit from a 9 V PP3 battery.
- A 3 inch speaker can be used as K1.
- All capacitors must be rated at least 15V.
- An 8 Ohm speaker or head phone can be connected at the output to hear the picked sound.
Electronic Eye
Description :
Electronic eye has much use in this electronic age. Also Known as magic eye. It can be used as an automatic guest indicator at the door, If fitted on the bottom of the door entrance. Once it is installed at the door there is no need to install a call bell. It can also be used at homes or in banks as a burglar alarm.
Fix the LDR to the wooden door or a locker to be protected in such a manner that when anybody tries to open it, a shadow falls on the LDR and the circuit gets activated and produce a pleasant sound through the buzzer.
This electronic eye circuit uses NOT gate from CMOS I.C CD 4049. CD 4049 contains 6 independent NOT gate in one package; we have used here (a) one only. NOT gate output goes high(1) when the input pin 3 is at lower then 1/3rd level of the supply voltage. Conversely the output goes low (0) when it is above 1/3rd level. So small change in the voltage of pin-2 is enough to change the level of output (pin-3) from 1 to 0 and 0 to 1. The output has only two states high and low and can not remain in any intermediate stage. It is powered by a 9V battery for portable use. The circuit is economic in power consumption. Pin 1 is connected to the positive supply and pin 8 is grounded.
To detect the present of an object we have used LDR and a source of light. LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has resistance of about 1 mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum.
We have made a potential divider circuit with LDR and 220 KΩ resistance connected in series. We know that voltage is directly proportional to conductance so more voltage we will get from this divider when LDR is getting light and low voltage in darkness. This divided voltage is given to input of NOT gate.
As soon as LDR gets dark the voltage of input not gate drops 1/3rd of the supply voltage and pin 2 gets high and LED or buzzer which is connected to the output gets activated.
Advantage of using Logic gate is that data can be easily send to other digital interface device ie one can easily fed data to computer using parallel port or for further processing .
Circuit Diagram :
Clap Switch
Description :
Here is a Hobby Circuit for electronics hobbyists that can switch on & off a light, Fan, Radio etc. by the sound of clap. The sound of clap is received by a small microphone that is shown biased by resistor R1 in the circuit. The microphone changes sound wave in to electrical wave which is further amplified by Q1. Transistor Q1 is used as common emitter circuit to amplify weak signals received by the microphone. Amplified output from the collector of transistor Q1 is then feed to the Bistable Multivibrator circuit also known as flip-flop circuit.
Flip flop circuit is made by using 2 Transistor, in our circuit Q2&Q3. In a flip-flop circuit, at a time only one transistor conduct and other cut off and when it gets a trigger pulse from outside source then first transistor is cutoff and 2nd transistor conducts. Thus output of transistor is either logic-0 or logic-1 and it remains in one state 0 or 1 until it gets trigger pulse from outer source.
The pulse of clap which is a trigger for flip-flop which makes changes to the output which is complementary (reverse). Output of flip-flop which is in the low current form is unable to drive relay directly so we have used a current amplifier circuit by using Q4 which is a common emitter circuit. Output of Q4 is connected to a Relay (Electromagnetic switch) which works like a mechanical switch and it becomes easy for connecting other electrical appliance.
The relay contact is connected to the power line and hence turns on/off any electrical appliance connected all the way through relay.
Circuit Diagram :
Circuit Elements :
Resistors
R1=15KΩ, R5,R6=1.5KΩ
R2,R11,R12=2.2MΩ, R13=2.2KΩ
R3=270KΩ, R4=3.3KΩ
R7,R8=10KΩ, R9,R10=27KΩ
Capacitors
C1=1000µf/16v
C2=.01µf,C3,C4=.047µf
Semi Conductors
Q1,Q2,Q3= BC548
D2,D3,D4= IN 4148
D1,D5=IN 4007, Q4=BC368
Misc
T1=12v/500mA Transformer
Mic= Condenser Microphone
K1= 12V Relay, B1= Bulb or Load
Mic= Condenser Microphone
K1= 12V Relay, B1= Bulb or Load
Touch Switch
Description :
THEAFS ARE ATTRACTED TO EXPENSIVE THINGS WHEN THEY COME IN OUR HOUSES. WE CAN PROTECT OUR PRODUCT OR THING BY MAKING THEM TOUCH PROOF OR WE CAN STOP ANY UNIDENTIFIED PERSONS ENTRY IN OUR HOUSE BY MAKING DOOR AND WINDOW TOUCH PROOF.THIS CIRCUIT ALERT US WHEN ANY THEAF COME TO STOLE PRODUCTS FROM OUR HOUSE OR TOUCH ANY METALLIC THING AT DOOR / WINDOW OR IN SIDE . WE CAN USE THIS CERCUIT TO PROTECT OUR CAR OR BIKE BY MAKING THEM TOUCH PROOF.
AS WE HAVE DISCRIBE ABOVE THIS PRODUCT GIVE ALARM WHEN ANY HUMAN BODY TOUCH ANY OF THE METTALIC THING WHICH ARE PROTECTED BY THIS CIRCUIT. THIS PROJECT IS WORKING ON TWO TRANSISTORS
WHICH MAKE COMPLIMENTORY PAIR DIRECT COUPLED AMPLIFIER. THIS CIRCUIT BASICALLY A AUDIO OSILATOR FOR OSILATION WE USE COLLECTOR OF TRANSISTOR BC558 WHICH IS CONNECTED TO THE BASE OF TRANSISTOR BC 548 VIA RESISTANCE 18 K .01 or .02 MFD CAPACITOR . TRANSISTOR BC-548 IS WORKING AS A PREAMPLIFIER.
WHEN ANY HUMAN BODY TOUCH THE TOUCH SENSOR WHICH IS CONNECTED TO BASE OF TRANSISTOR BC-548. THIS TRANSISTOR CONDUCT WITH HUMAN SKIN CONDUCTANCE . WHEN TRANSISTOR BC-548 START CONDUCTING IT’S FORCED TO TRANSISTOR BC558 TO START CONDUCTING . SO WE GET ALARM SOUND FROM SPEAKER. WHEN WE TAKE BACK OUR HAND THEN DOES NOT CONNECTED TO BASE OF TRANSISTOR BC-548 . SO IT’S DOES NOT CONDUCT WE DO NOT GET THE ALARM SOUND.
THEAFS ARE ATTRACTED TO EXPENSIVE THINGS WHEN THEY COME IN OUR HOUSES. WE CAN PROTECT OUR PRODUCT OR THING BY MAKING THEM TOUCH PROOF OR WE CAN STOP ANY UNIDENTIFIED PERSONS ENTRY IN OUR HOUSE BY MAKING DOOR AND WINDOW TOUCH PROOF.THIS CIRCUIT ALERT US WHEN ANY THEAF COME TO STOLE PRODUCTS FROM OUR HOUSE OR TOUCH ANY METALLIC THING AT DOOR / WINDOW OR IN SIDE . WE CAN USE THIS CERCUIT TO PROTECT OUR CAR OR BIKE BY MAKING THEM TOUCH PROOF.
AS WE HAVE DISCRIBE ABOVE THIS PRODUCT GIVE ALARM WHEN ANY HUMAN BODY TOUCH ANY OF THE METTALIC THING WHICH ARE PROTECTED BY THIS CIRCUIT. THIS PROJECT IS WORKING ON TWO TRANSISTORS
WHICH MAKE COMPLIMENTORY PAIR DIRECT COUPLED AMPLIFIER. THIS CIRCUIT BASICALLY A AUDIO OSILATOR FOR OSILATION WE USE COLLECTOR OF TRANSISTOR BC558 WHICH IS CONNECTED TO THE BASE OF TRANSISTOR BC 548 VIA RESISTANCE 18 K .01 or .02 MFD CAPACITOR . TRANSISTOR BC-548 IS WORKING AS A PREAMPLIFIER.
WHEN ANY HUMAN BODY TOUCH THE TOUCH SENSOR WHICH IS CONNECTED TO BASE OF TRANSISTOR BC-548. THIS TRANSISTOR CONDUCT WITH HUMAN SKIN CONDUCTANCE . WHEN TRANSISTOR BC-548 START CONDUCTING IT’S FORCED TO TRANSISTOR BC558 TO START CONDUCTING . SO WE GET ALARM SOUND FROM SPEAKER. WHEN WE TAKE BACK OUR HAND THEN DOES NOT CONNECTED TO BASE OF TRANSISTOR BC-548 . SO IT’S DOES NOT CONDUCT WE DO NOT GET THE ALARM SOUND.
Circuit Diagram :
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