Simple Audio Power Amplifier Circuit

Simple Audio Power Amplifier Circuit

The circuit illustrated here is probably the simplest form of an audio power amplifier. Though the circuit is very crude by its specs yetis able to amplify an audio input up to a powerful 4 watts in a 8 Ohm speaker.The transistor is a 2N3055 is used as a switch for inducing voltages in response to the input signals into one half winding of the transformer. The back emf generated across the winding of the transformer is effectively dumped over the speaker generating the required amplifications. The transistor needs to be mounted on a suitable heatsink.

Temperature Control Circuit by Fan

The circuit is temperature control by fan, this circuit can control temperature and it also indicates the temperature. All the above functions are monitored and controlled by the 8 bit microcontroller AT89S52. The system will get the temperature from the IC DS1820 and it will control the speed according the values stored in the code.? The System is fully controlled by the microcontroller AT89S52.  Here is a schematic drawing:

Smoke alarm circuit

Here is a smoke alarm circuit from the Internet:



I realize it uses a speaker and not a piezo. The point to be made is that that circuit will not pass DC current to activate a DC relay. Your circuit may have a similar oscillator/piezo driver. In order to help you more, we need to know a bit more about the circuit in your smoke detector.

Circuit Solar Tracker with Servo Motor Proposal

Arduino Solar Tracker with ServoMotor

This circuit was tested and worked properly!

This solar tracker system uses the Arduino UNO board, a servomotor, 2 LDRs and 2 resistors to rotate the solar panel towards the Sun or a source of light. Here
I have a standard servo that can rotate approximately 180 degrees (90° in each direction) and is controlled using the included Arduino’s Servo Library. The code is simple too and I’ll try to explain it after this video where I made a short presentation of the project in action. Unfortunately I had no solar panel at that moment.
Here is the Sketch Code:

#include <Servo.h> 
 
Servo myservo; 
int pos = 90;   // initial position
int sens1 = A0; // LRD 1 pin
int sens2 = A1; //LDR 2 pin
int tolerance = 2;
 
void setup() 
{ 
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object 
  pinMode(sens1, INPUT);
  pinMode(sens2, INPUT);
  myservo.write(pos);
  delay(2000); // a 2 seconds delay while we position the solar panel
}  
 
void loop() 
{ 
  int val1 = analogRead(sens1); // read the value of sensor 1
  int val2 = analogRead(sens2); // read the value of sensor 2
 
  if((abs(val1 - val2) <= tolerance) || (abs(val2 - val1) <= tolerance)) {
    //do nothing if the difference between values is within the tolerance limit
  } else {    
    if(val1 > val2)
    {
      pos = --pos;
    }
    if(val1 < val2) 
    {
      pos = ++pos;
    }
  }
 
  if(pos > 180) { pos = 180; } // reset to 180 if it goes higher
  if(pos < 0) { pos = 0; } // reset to 0 if it goes lower
  
  myservo.write(pos); // write the position to servo
  delay(50);
}

Inside the code we use the “pos” variable to set the initial position of the servo to 90, the mid position. The 2 LDRs are connected to pin A0 and A1 on the board. The “tolerance” variable is used for allowing a small tolerance otherwise the solar panel would be continously adjusting its position.
In the setup() function we set the pins were the LDR are connected as INPUTs and position the servo motor at 90° then wait for a 2 seconds before the code execution inside the loop(). In the loop() we read the values received from our 2 sensors and adjust the solar panel based on these values.

Schematic of the Arduino Solar Tracker Circuit

As you can see in the schematic all that you need to make the electrical part is the board, one servo, 2 LDRs and 2 x 10K resistors. Usually the servo has a yellow wire that is used to control the rotation and it must be connected on pin 9 on the board.
The 2 LDRs (light dependent resistors) must be positioned the same way as the ones showned here at a slightly different angle. If your servo acts weird try to connect a 470µF/10V capacitor between the +5V and GND.

Traffic Light System proposal

Arduino Traffic Light System

This circuit was tested and worked properly!

 

Here is a traffic light system based on Arduino that can be use in a 3-way ond 4-way intersections. It has an additional blinking orange led that is used to signal when the pedestrians can cross the street. The code is a little bit complicated but I think you can understand how it works, right?

Check out this video below to see how the traffic lights system is working.
The code is written based on 4 situations:

1. the first traffic light (TF1) has the red signal and the pedestrians ON; the second one (TF2) has green ON.
2. TF1 has red and yellow ON; TF2 has yellow ON
3. TF1 is green now and TF2 is red and pedestrians ON
4. TF1 is yellow and TF2 is red and yellow

The schematic is too easy, all you have to do is connect the leds in series with a 470Ω resistor between the ground and the Arduino pins mentioned in the code.

Code of the Arduino Traffic Lights Sketch

// Source: http://www.electroschematics.com/10178/arduino-traffic-light-system/
int trafficLights1[] = {2,3,4,5};	// red, yellow, green, pedestrians led pins
int trafficLights2[] = {6,7,8,9};	// red, yellow, green, pedestrians led pins
int situations = 4;
int duration[] = {8000,3000,10000,3000}; // duration of each situation
long previousCars = 0;
long previousPeds = 0;
long interval = 300;	//blink interval for pedestrians
int ledState = LOW;
int state;
int i = 0;

void setup()
{
  for(int i = 0; i < 4; i++) {
	  pinMode(trafficLights1[i], OUTPUT);
	  pinMode(trafficLights2[i], OUTPUT);
  }
	Serial.begin(9600);
}

void loop()
{	
	unsigned long currentMillis = millis();		
	if(currentMillis - previousCars < duration[i]) {			
		situation(i);		
	} else { 
		previousCars = currentMillis; 
		if(i >= situations) {
			i = 0;
			} else {
			i++;
		}		
	}
}

void activateTrafficLight1(String lights, int pedestrians) 
{	
	for(int x = 0; x < 3; x++) 
	{
		if(lights[x] == '0') state = LOW;
		if(lights[x] == '1') state = HIGH;
		digitalWrite(trafficLights1[x], state);	
	}
	if(pedestrians == 1) {
		blinkPed(trafficLights1[3]);
	} else {
		digitalWrite(trafficLights1[3], LOW);
	}
}

void activateTrafficLight2(String lights, int pedestrians)
{	
	for(int x = 0; x < 3; x++)
	{
		if(lights[x] == '0') state = LOW;
		if(lights[x] == '1') state = HIGH;
		digitalWrite(trafficLights2[x], state);
	}
	if(pedestrians == 1) {
		blinkPed(trafficLights2[3]);
	} else {
		digitalWrite(trafficLights2[3], LOW);
	}
}

void situation(int i)
{
	switch(i){
		case 0: 
			activateTrafficLight1("100",1); // 100 means red ON, yellow OFF, green OFF
			activateTrafficLight2("001",0); // the second parameter is for pedestrians
			break;							// 1 is ON and 0 is OFF
		case 1: 
			activateTrafficLight1("110",0); // 110: red ON, yellow ON, green OFF
			activateTrafficLight2("010",0);
			break;	
		case 2: 
			activateTrafficLight1("001",0);
			activateTrafficLight2("100",1);
			break;
		case 3:	
			activateTrafficLight1("010",0);
			activateTrafficLight2("110",0);
			break;	
	}
}

void blinkPed(int ped) {
	unsigned long currentMillis = millis();
	if(currentMillis - previousPeds > interval) {		
		previousPeds = currentMillis;		
		if (ledState == LOW)
		ledState = HIGH;
		else
		ledState = LOW;
		digitalWrite(ped, ledState);
	}	
}

AM receiver circuit

AM receiver circuit

Description.

Here is a low cost AM receiver circuit that can be tuned from around 550 to 1100 KHz. Three transistors are used in this project. The transistors Q1 and Q2 are wired as a compound transistor pair in which Q1 is an emitter follower and Q2 is a common emitter amplifier. The emitter follower prevents the loading of tank circuit, while the common emitter amplifier necessary voltage gain. The L1 and C2 forms the tank circuit.The L1 also does the job of antenna.The series combination of R6 and R7 gives a regenerative feedback between output of the Q2 and tank circuit. The transistor Q3 performs the demodulation of the carrier signal. It also provides amplification the demodulated signal. The audio output is coupled out from the collector of Q3 via the capacitor C3.Capacitor C6 provides some noise filtering.

Circuit diagram.


Notes.

• The circuit can be assembled on a general purpose PCB.
• Use a 9V PP3 battery for powering the circuit.
• R7 can be used to adjust the sensitivity and selectivity of the circuit.
• A high impedance head phone can be used for listening the radio.
• For L1 make 60 turns of 26 SWG enameled copper wire on a 3/8 inch diameter, 3inch long ferrite rod.
• The moving plates of C2 must be connected to the base of Q1 and fixed plates must be connected to the junction of C3 and R6.Reversing the connection may decrease the stability.

Simple Automatic Emergency Lamp Circuit

Simple Automatic Emergency Lamp Circuit



This simple emergency lamp circuit uses very components and yet is able to provide some useful service. The shown device is able to switch ON automatically when mains power fails, illuminating all the connected LEDs.As soon as power is restored, the LEDs shut off automatically and the connected starts charging through the built in power supply. The circuit employs a transformerless power supply for initiating the explained automatic actions and also for trickle charging the connected battery.

Parts List for the above CIRCUIT DIAGRAM

R1 = 220K,
R2 = 10K,
D1, D2, D3 = 1N4007,
Z1 = 15V 1watt, zener diode,
C1 = 105/400V
C2 = 100uF/25V
T1 = 2N2907, or 8550, or BD 140
Z1 = 12V, 1 watt
LEDs = white, high bright type.

Automatic Day Night Light Switch Circuit



This simple transistor circuit can be used for monitoring the dawn and dusk conditions and for switching lights in response to the varying conditions. Thus the circuit can be used for switching ON the connected lights when night sets in and switch it OFF during day break. The threshold tripping point may be set by adjusting the 10K preset.
The capacitors are 100uF/25V, the transistors are ordinaryBC547, and the diodes are 1N4007.

Electronic Candle Circuit




This is a simple hobby project and exhibits all the properties of a conventional wax type candle. Here the LED is used in place of the candle flame, which illuminates as soon as the mains power fails and shuts off automatically when the power is restored. So it also performs the function of an emergency lamp. The connected battery is used for powering the candle”light and it is charged continuously when the unit is not being used and powered through the mains supply.

An interesting “puff off” feature is also included so tatthe “candle” light may be switched OFF whenever desired through a puff of airinto the attached mic which acts as the air vibration sensor.

Simple Emergency Flashlight Circuit

This circuit may be used as an automatic emergency lamp when there’s no power or when mains power fails during night times. As shown in the diagram, the circuit utilizes a cheap incandescent flashlight bulb for the required illumination. As long as the input supply from the mains transformer is present the transistor remains switched OFF and so does the lamp. However the moment the mains power fails, the transistor conducts and switches ON the battery power to the bulb, instantly illuminating it brightly.

The battery is trickle charged for so long as the mainspower remains connected to the circuit.

Parts List

R1 = 22 Ohms,
R2 = 1K,
D1 = 1N4007,
T1 = 8550,
Lamp = 3V flashlight bulb.
Transformer = 0-3V, 500 mA,
Battery = 3V, penlight 1.5 V cells (2nos. in series)

Music operated Dancing Light Circuit




This circuit may be used for transforming music into dancing light patterns. The operation of the circuit is very simple, the music input is fed to the bases of the shown transistor array, each of them are configured to conduct at a specific voltage level in the incrementing order from the top to the bottom transistor.

Thus the uppermost transistor conducts with the input music is at the minimum volume level and the subsequent transistor starts to conduct in sequence as per the volume or the pitch of the music. Each transistor is rigged with individual lamps which light up in response to the music levels in a “chasing” dancing light pattern.

Parts List

All the base presets are = 10K,
All the collector resistors are 470 Ohms,
All the diodes are = 1N4148,
All NPN transistors are = BC547,
The single PNP transistor is = BC557,
All the triacs are = BT136,
The input capacitor = 0.22uF/25V non polar.

Simple Clap Switch Circuit

The interesting clap switch circuit shown here can be used in stairways and passages for illuminating the premise momentarily through clap sound. The circuit is basically a sound sensor circuit with an enclosed amplifier stage. The clap sound or any similar sound is detected by the mic and converted into minute electrical pulses. These electrical pulses are suitably amplified by the subsequent transistor stage.

The Darlington stage shown at the output is the timer stage which switches in response to the above sound interaction and illuminate the connected LEDs for some period of time defined by the 220K resistor and the two39 K resistors. After the time lapses the LEDs are switched off automatically and the circuit returns to its original state until the next clap sound is detected.

The parts list is given in the circuit diagram itself.

A Simple ELCB Circuit



The circuit shown here can be used for detecting earth leakage conditions and for implementing the required shutting off the mains power supply. Unlike usual configurations, here the ground to the circuit and the relay is acquired from the earthing line itself. Also since the input coil is also referenced to the common earthing ground, the entire functioning becomes compatible and accurate.

On sensing a possible current leakage at the input, the transistors come into action and switch the relays appropriately. The two relay have their individual specific roles to play. One relay detects and switches OFF when there’s current leakage through an appliances body, while the other relay is wired up to sense the presence of a the earthing line and switches OFF the mains as soon a wrong or weak earthing line is detected.

Parts List
R1 = 33K,
R2 = 4K7,
R3 = 10K,
R4 = 220 Ohms,
R5 = 1K,
R6 = 1M,
C1 = 0.22uF,
C2, C3, C4 = 100uF/25V
C5 = 105/400V
All diodes = 1N4007,
Relay = 12V, 400 Ohms
T1, T2 = BC547,
T3 = BC557,
L1 = output transformer as used in radio push pull amplifierstage
Simple LED Flasher




A very simple LED flasher circuit is illustrated in the diagram. The transistors and the corresponding parts are connected in the standard astable multivibrator mode, which forces the circuit to oscillate the moment power is applied. The LEDs connected at the collector of the transistors start flashing alternately in wig wag manner. The LEDs shown in the diagram are connected in series and parallel, so that many numbers of LEDs can be accommodated in the configuration. The pots P1 and P2 may be adjusted for getting different interesting flashing patterns with the LEDs.

Parts List

R1, R2 = 1K,
P1,P2 = 100K pots,

C1, C2 = 33uF/25V,
T1, T2 = BC547,
Resistors connected with each LED series = 470 Ohms
LEDs are 5mm type, color as per choice.

Simple Wireless Microphone Circuit


Anything spoken into the mic of the presented circuit cab be clearly picked up and reproduced by any standard FM radio, within a range of 30meters of distance. The circuit is very simple and just requires ther shown components to be assembled and connected with each other as depicted in the diagram.
The coil L1 consists of 5 turns of 1mm super enameled copper wire, having a diameter of around 0.6 cm.

Parts List

R1 = 4K7,
R2 = 82K,
R3 = 1K,
C1 = 10pF,
C2, C3 = 27pF,
C4 = 0.001uF,
C5 = 0.22uF,
T1 = BC547
40 LED Emergency Light Circuit




The shown design of a 40 LED emergency light is driven usingan ordinary transistor/transformer inverter circuit. The transistor and the respective winding of th transformer are configured as a high frequency oscillator stage. The oscillations induce a high voltage across the winding of the transformer. The stepped-up voltage at the output is directly used to drive the LED which are all connected in series for getting the desired balance and the illumination.

Parts List

R1 = 470 Ohms,
VR1 = 47K,
C1, C2 = 1uF/25V
TR1 = 0-6V, 500mA,
Battery = 6V, 2AH,
LEDs = high bright white, 40 nos.

Simple Transistor Latch Circuit

If you are looking for a circuit which can be used to latch the output in response to an input signal, then this circuit can be used for the intended purpose very effectively and also very cheaply.

A momentary input trigger is applied to the base of T1,which switches it for a fraction of a second depending upon the length of the applied signal. The conduction of T1 immediately switches T2 and the connected relay. However at the very instant a feedback voltage also appears at the base of T1 via R3 from the collector of T2. This feed back voltage instantly latches the circuit and keeps the relay activated even after the trigger from the input is removed.

Parts List

R1, R3 = 100k,
R2, R4 = 10K,
C1 = 1uF/25V
D1 = 1N4148,
T1 = BC547,
T2 = BC557
Relay = 12V, SPDT

Simple LED Music Light Circuit

In one of the previous sections we studied a simple music light show circuit using mains operated incandescent lamps, the present design incorporate LEDs for similar intended light show generation. As can be seen in the figure, the transistors are all wired up in sequencing array. The music signal varying with pitch and amplitude is applied at the base of the buffer amplifier PNP transistor. The amplified music is then fed across the whole array where the respective transistor receive the inputs with incrementing pitch or the volume levels and go on switching in the corresponding manner from start to finish, producing an interesting LED light sequencing pattern. This light exactly varies its length according to the pitch or the volume of the fed music signal.

Parts list is provided in the diagram.

A Simple 2-Pin Automobile Indicator Lamp Flasher Circuit with Buzzer

If you want to make a flasher unit for you motorbike then this circuit is just for you. This simple turn signal flasher circuit can be easily built and installed in any two wheelers for the desired actions. The circuit employs just two 2-pins instead of 3 as found in other flasher circuits. Once installed, the circuit will faithfully flash the side indicator lights whenever the intended function is switched ON. The circuit also incorporates an optional buzzer circuit which can be also included for getting a beeping sound in response to the flashing of the lamps.

Parts List

R1, R2, R3 = 10K
R4= 33K
T1 = D1351,
T2 = BC547,
T3 = BC557,
C1, C2 = 33uF.25V
L1 = Buzzer Coil

Simple Relay Motorbike Flasher Circuit


In the above section we discussed a simple three transistor based flasher circuit; here we study another similar design, however here we incorporate a relay for the switching actions of the lamps.

The circuit looks pretty straightforward and employs hardly anything substantial and yet performs the expected functions wonderfully well.

Just build it and wire it in your mo-bike for witnessing the intended functions...

Parts List

R1 = 1K,
R2 = 4K7,
T1 = BC557,
C1 = 100uF/25V,
C2 = 1000uF/25V
Relay = 12V, 400 Ohms
D1 = 1N4007

Simple Door Bell Timer, with Adjustable Timing Facility

Yes this simple transistor circuit can be used as a home door bell and it’s ON time can be set as preferred by the user, meaning if you wanted that the sound of the bell to remain switched ON for a particular period of time, you could easily do it just by adjusting the given pot.
The actual tune is derived from the IC UM66 and the associated components, while all the included transistors along with the relay are configured for producing the time delay for keeping the music switched ON.

Parts List

R1, R2, R4, R5 = 1K
VR1 = 100K,
D1, D2 = 1N4007,
C1, C2 = 100uF/25
T1 = BC547,
T2 = BC557
T3 = 2N2222
Z1 = 3V/400mW
Transformer = 0-12V/500mA,
S1 = Bell Push
IC = UM66

Timer Circuit with Independent On and OFF Delay Adjust Facility


The circuit can be used for generating delays at a desired rate. The On time of the relay can be controlled by adjusting the Pot VR1 while the pot VR2 may be used to decide after how long the relay responds once theinput trigger is fed by the switch S1.

The parts list is enclosed inside the diagram.

Simple High and Low Mains Voltage Cut Off Circuit



Are you having problems with your input Mains supply? That’s common problem associated with our input mains AC line, where a high and a low voltage conditions are quite frequently encountered by us. The simple circuit shown here can be built and installed in you house electrical board for getting a 24/7 safety from the possible dangerous AC voltage conditions. The circuit keeps the relay and the wired appliances as long as the mains input stays within a safe tolerable level and switches the load OFF the moment a dangerous or unfavorable voltage condition is sensed by the circuit.

Parts List

R1, R2 = 1K,
P1, P2 = 10K Preset,
T1, T2 = BC547B,
C1 = 100uF/25V,
D1 = 1N4007
RL1 = 12V, SPDT,
TR1 = 0-12V, 500mA
0 – 40 V, 0 – 4 Amp Continuously Variable Power SupplyCircuit



This unique work bench circuit utilizes only a few inexpensive transistors and yet delivers some truly useful features. The feature includes continuously variable voltage from zero to the maximum transformer voltage and current variable from zero to the maximum applied input level. The output of this power supply is also over load protected. The pot P1 is used for setting the maximum current while the pot P2 is used for varying the output voltage level up to the desired levels.

Parts List
R1 = 1K2,
R2 = 100 Ohms,
R3 = 470 Ohms,
R4 = Evaluate using Ohms law.
R5 = 1K8,
R6 = 4k7,
R7 = 68 Ohms,
R8 = 1k8,
T1 = 2N3055,

T2, T3 = BC 547B,
D1 = 1N4007,
D2, D3, D4, D5 = 1N5408,
C1, C2 = 2200uF/50V,
Tr1 = 0 – 35 Volts, 3 Amp

Simple Crystal Tester Circuit

When it comes to frequency generating circuits or rather precise oscillator circuits, crystals become a crucial part, especially because they play an important role for generating and maintaining accurate frequency rates of the particular circuit. However these devices are prone to many defects and are normally difficult to check through conventional DMM units.

The shown circuit can be used for checking all types of crystals instantly. The circuit itself is a small transistor oscillator circuit which starts oscillating when a good crystal is introduced across the indicated points in the circuit. If the crystal is a good one, the bulb lights up showing the relevant results and if there’s any defect in the attached crystal, the bulb remains switched OFF.

Simple Current Limiter Circuit Using two transistors

In many critical applications, circuits are required to maintain a strict controlled magnitude of current through them of at their outputs. The proposed circuit is exactly meant for carrying out the discussed function. The lower transistor is the main output transistor which operates the output vulnerable load and by itself is unable to control the current through it. The introduction of the upper transistor makes it sure that the base of the lower transistor is allowed to conduct as long as the current output is within the specified limits. In case the current tends to cross the limits, the upper transistor conducts and switches OFF the lower transistor inhibiting any further passage of the exceeded current limit. The threshold current may be fixed by R which is calculated with the shown formula

Transistor Power Amplifier Circuit

100 Watt Transistor Power Amplifier Circuit




This circuit of a transistor power amplifier is outstanding with its performance and is able to provide a thumping 100 watts of pure music output. As can be seen in the diagram it utilizes mainly transistors for the implementations and a handful of other inexpensive passive components like resistors and capacitors. The required input is not more than 1 V, which gets amplified 200,000 times at the output.

Simple Automatic Emergency Lamp Circuit



This simple emergency lamp circuit uses very components and yet is able to provide some useful service. The shown device is able to switch ON automatically when mains power fails, illuminating all the connected LEDs.As soon as power is restored, the LEDs shut off automatically and the connected starts charging through the built in power supply. The circuit employs a transformerless power supply for initiating the explained automatic actions and also for trickle charging the connected battery.

Parts List for the above CIRCUIT DIAGRAM

R1 = 220K,
R2 = 10K,
D1, D2, D3 = 1N4007,
Z1 = 15V 1watt, zener diode,
C1 = 105/400V
C2 = 100uF/25V
T1 = 2N2907, or 8550, or BD 140
Z1 = 12V, 1 watt
LEDs = white, high bright type.

Automatic Day Night Light Switch Circuit



This simple transistor circuit can be used for monitoring the dawn and dusk conditions and for switching lights in response to the varying conditions. Thus the circuit can be used for switching ON the connected lights when night sets in and switch it OFF during day break. The threshold tripping point may be set by adjusting the 10K preset.
The capacitors are 100uF/25V, the transistors are ordinaryBC547, and the diodes are 1N4007.

Electronic Candle Circuit




This is a simple hobby project and exhibits all the properties of a conventional wax type candle. Here the LED is used in place of the candle flame, which illuminates as soon as the mains power fails and shuts off automatically when the power is restored. So it also performs the function of an emergency lamp. The connected battery is used for powering the candle”light and it is charged continuously when the unit is not being used and powered through the mains supply.

An interesting “puff off” feature is also included so tatthe “candle” light may be switched OFF whenever desired through a puff of airinto the attached mic which acts as the air vibration sensor.

Simple Emergency Flashlight Circuit

This circuit may be used as an automatic emergency lamp when there’s no power or when mains power fails during night times. As shown in the diagram, the circuit utilizes a cheap incandescent flashlight bulb for the required illumination. As long as the input supply from the mains transformer is present the transistor remains switched OFF and so does the lamp. However the moment the mains power fails, the transistor conducts and switches ON the battery power to the bulb, instantly illuminating it brightly.

The battery is trickle charged for so long as the mainspower remains connected to the circuit.

Parts List

R1 = 22 Ohms,
R2 = 1K,
D1 = 1N4007,
T1 = 8550,
Lamp = 3V flashlight bulb.
Transformer = 0-3V, 500 mA,
Battery = 3V, penlight 1.5 V cells (2nos. in series)

Music operated Dancing Light Circuit




This circuit may be used for transforming music into dancing light patterns. The operation of the circuit is very simple, the music input is fed to the bases of the shown transistor array, each of them are configured to conduct at a specific voltage level in the incrementing order from the top to the bottom transistor.

Thus the uppermost transistor conducts with the input music is at the minimum volume level and the subsequent transistor starts to conduct in sequence as per the volume or the pitch of the music. Each transistor is rigged with individual lamps which light up in response to the music levels in a “chasing” dancing light pattern.

Parts List

All the base presets are = 10K,
All the collector resistors are 470 Ohms,
All the diodes are = 1N4148,
All NPN transistors are = BC547,
The single PNP transistor is = BC557,
All the triacs are = BT136,
The input capacitor = 0.22uF/25V non polar.

Simple Clap Switch Circuit

The interesting clap switch circuit shown here can be used in stairways and passages for illuminating the premise momentarily through clap sound. The circuit is basically a sound sensor circuit with an enclosed amplifier stage. The clap sound or any similar sound is detected by the mic and converted into minute electrical pulses. These electrical pulses are suitably amplified by the subsequent transistor stage.

The Darlington stage shown at the output is the timer stage which switches in response to the above sound interaction and illuminate the connected LEDs for some period of time defined by the 220K resistor and the two39 K resistors. After the time lapses the LEDs are switched off automatically and the circuit returns to its original state until the next clap sound is detected.

The parts list is given in the circuit diagram itself.

A Simple ELCB Circuit



The circuit shown here can be used for detecting earth leakage conditions and for implementing the required shutting off the mains power supply. Unlike usual configurations, here the ground to the circuit and the relay is acquired from the earthing line itself. Also since the input coil is also referenced to the common earthing ground, the entire functioning becomes compatible and accurate.

On sensing a possible current leakage at the input, the transistors come into action and switch the relays appropriately. The two relay have their individual specific roles to play. One relay detects and switches OFF when there’s current leakage through an appliances body, while the other relay is wired up to sense the presence of a the earthing line and switches OFF the mains as soon a wrong or weak earthing line is detected.

Parts List
R1 = 33K,
R2 = 4K7,
R3 = 10K,
R4 = 220 Ohms,
R5 = 1K,
R6 = 1M,
C1 = 0.22uF,
C2, C3, C4 = 100uF/25V
C5 = 105/400V
All diodes = 1N4007,
Relay = 12V, 400 Ohms
T1, T2 = BC547,
T3 = BC557,
L1 = output transformer as used in radio push pull amplifierstage
Simple LED Flasher




A very simple LED flasher circuit is illustrated in the diagram. The transistors and the corresponding parts are connected in the standard astable multivibrator mode, which forces the circuit to oscillate the moment power is applied. The LEDs connected at the collector of the transistors start flashing alternately in wig wag manner. The LEDs shown in the diagram are connected in series and parallel, so that many numbers of LEDs can be accommodated in the configuration. The pots P1 and P2 may be adjusted for getting different interesting flashing patterns with the LEDs.

Parts List

R1, R2 = 1K,
P1,P2 = 100K pots,

C1, C2 = 33uF/25V,
T1, T2 = BC547,
Resistors connected with each LED series = 470 Ohms
LEDs are 5mm type, color as per choice.

Simple Wireless Microphone Circuit


Anything spoken into the mic of the presented circuit cab be clearly picked up and reproduced by any standard FM radio, within a range of 30meters of distance. The circuit is very simple and just requires ther shown components to be assembled and connected with each other as depicted in the diagram.
The coil L1 consists of 5 turns of 1mm super enameled copper wire, having a diameter of around 0.6 cm.

Parts List

R1 = 4K7,
R2 = 82K,
R3 = 1K,
C1 = 10pF,
C2, C3 = 27pF,
C4 = 0.001uF,
C5 = 0.22uF,
T1 = BC547
40 LED Emergency Light Circuit




The shown design of a 40 LED emergency light is driven usingan ordinary transistor/transformer inverter circuit. The transistor and the respective winding of th transformer are configured as a high frequency oscillator stage. The oscillations induce a high voltage across the winding of the transformer. The stepped-up voltage at the output is directly used to drive the LED which are all connected in series for getting the desired balance and the illumination.

Parts List

R1 = 470 Ohms,
VR1 = 47K,
C1, C2 = 1uF/25V
TR1 = 0-6V, 500mA,
Battery = 6V, 2AH,
LEDs = high bright white, 40 nos.

Simple Transistor Latch Circuit

If you are looking for a circuit which can be used to latch the output in response to an input signal, then this circuit can be used for the intended purpose very effectively and also very cheaply.

A momentary input trigger is applied to the base of T1,which switches it for a fraction of a second depending upon the length of the applied signal. The conduction of T1 immediately switches T2 and the connected relay. However at the very instant a feedback voltage also appears at the base of T1 via R3 from the collector of T2. This feed back voltage instantly latches the circuit and keeps the relay activated even after the trigger from the input is removed.

Parts List

R1, R3 = 100k,
R2, R4 = 10K,
C1 = 1uF/25V
D1 = 1N4148,
T1 = BC547,
T2 = BC557
Relay = 12V, SPDT

Simple LED Music Light Circuit

In one of the previous sections we studied a simple music light show circuit using mains operated incandescent lamps, the present design incorporate LEDs for similar intended light show generation. As can be seen in the figure, the transistors are all wired up in sequencing array. The music signal varying with pitch and amplitude is applied at the base of the buffer amplifier PNP transistor. The amplified music is then fed across the whole array where the respective transistor receive the inputs with incrementing pitch or the volume levels and go on switching in the corresponding manner from start to finish, producing an interesting LED light sequencing pattern. This light exactly varies its length according to the pitch or the volume of the fed music signal.

Parts list is provided in the diagram.

A Simple 2-Pin Automobile Indicator Lamp Flasher Circuit with Buzzer

If you want to make a flasher unit for you motorbike then this circuit is just for you. This simple turn signal flasher circuit can be easily built and installed in any two wheelers for the desired actions. The circuit employs just two 2-pins instead of 3 as found in other flasher circuits. Once installed, the circuit will faithfully flash the side indicator lights whenever the intended function is switched ON. The circuit also incorporates an optional buzzer circuit which can be also included for getting a beeping sound in response to the flashing of the lamps.

Parts List

R1, R2, R3 = 10K
R4= 33K
T1 = D1351,
T2 = BC547,
T3 = BC557,
C1, C2 = 33uF.25V
L1 = Buzzer Coil

Simple Relay Motorbike Flasher Circuit


In the above section we discussed a simple three transistor based flasher circuit; here we study another similar design, however here we incorporate a relay for the switching actions of the lamps.

The circuit looks pretty straightforward and employs hardly anything substantial and yet performs the expected functions wonderfully well.

Just build it and wire it in your mo-bike for witnessing the intended functions...

Parts List

R1 = 1K,
R2 = 4K7,
T1 = BC557,
C1 = 100uF/25V,
C2 = 1000uF/25V
Relay = 12V, 400 Ohms
D1 = 1N4007

Simple Door Bell Timer, with Adjustable Timing Facility

Yes this simple transistor circuit can be used as a home door bell and it’s ON time can be set as preferred by the user, meaning if you wanted that the sound of the bell to remain switched ON for a particular period of time, you could easily do it just by adjusting the given pot.
The actual tune is derived from the IC UM66 and the associated components, while all the included transistors along with the relay are configured for producing the time delay for keeping the music switched ON.

Parts List

R1, R2, R4, R5 = 1K
VR1 = 100K,
D1, D2 = 1N4007,
C1, C2 = 100uF/25
T1 = BC547,
T2 = BC557
T3 = 2N2222
Z1 = 3V/400mW
Transformer = 0-12V/500mA,
S1 = Bell Push
IC = UM66

Timer Circuit with Independent On and OFF Delay Adjust Facility


The circuit can be used for generating delays at a desired rate. The On time of the relay can be controlled by adjusting the Pot VR1 while the pot VR2 may be used to decide after how long the relay responds once theinput trigger is fed by the switch S1.

The parts list is enclosed inside the diagram.

Simple High and Low Mains Voltage Cut Off Circuit



Are you having problems with your input Mains supply? That’s common problem associated with our input mains AC line, where a high and a low voltage conditions are quite frequently encountered by us. The simple circuit shown here can be built and installed in you house electrical board for getting a 24/7 safety from the possible dangerous AC voltage conditions. The circuit keeps the relay and the wired appliances as long as the mains input stays within a safe tolerable level and switches the load OFF the moment a dangerous or unfavorable voltage condition is sensed by the circuit.

Parts List

R1, R2 = 1K,
P1, P2 = 10K Preset,
T1, T2 = BC547B,
C1 = 100uF/25V,
D1 = 1N4007
RL1 = 12V, SPDT,
TR1 = 0-12V, 500mA
0 – 40 V, 0 – 4 Amp Continuously Variable Power SupplyCircuit



This unique work bench circuit utilizes only a few inexpensive transistors and yet delivers some truly useful features. The feature includes continuously variable voltage from zero to the maximum transformer voltage and current variable from zero to the maximum applied input level. The output of this power supply is also over load protected. The pot P1 is used for setting the maximum current while the pot P2 is used for varying the output voltage level up to the desired levels.

Parts List
R1 = 1K2,
R2 = 100 Ohms,
R3 = 470 Ohms,
R4 = Evaluate using Ohms law.
R5 = 1K8,
R6 = 4k7,
R7 = 68 Ohms,
R8 = 1k8,
T1 = 2N3055,

T2, T3 = BC 547B,
D1 = 1N4007,
D2, D3, D4, D5 = 1N5408,
C1, C2 = 2200uF/50V,
Tr1 = 0 – 35 Volts, 3 Amp

Simple Crystal Tester Circuit

When it comes to frequency generating circuits or rather precise oscillator circuits, crystals become a crucial part, especially because they play an important role for generating and maintaining accurate frequency rates of the particular circuit. However these devices are prone to many defects and are normally difficult to check through conventional DMM units.

The shown circuit can be used for checking all types of crystals instantly. The circuit itself is a small transistor oscillator circuit which starts oscillating when a good crystal is introduced across the indicated points in the circuit. If the crystal is a good one, the bulb lights up showing the relevant results and if there’s any defect in the attached crystal, the bulb remains switched OFF.

Simple Current Limiter Circuit Using two transistors

In many critical applications, circuits are required to maintain a strict controlled magnitude of current through them of at their outputs. The proposed circuit is exactly meant for carrying out the discussed function. The lower transistor is the main output transistor which operates the output vulnerable load and by itself is unable to control the current through it. The introduction of the upper transistor makes it sure that the base of the lower transistor is allowed to conduct as long as the current output is within the specified limits. In case the current tends to cross the limits, the upper transistor conducts and switches OFF the lower transistor inhibiting any further passage of the exceeded current limit. The threshold current may be fixed by R which is calculated with the shown formula.