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Simple Hobby Electronic Circuits

A few of the interesting and useful hobby electronic circuit diagrams already published in this blog have been selected and compiled here for quick reference and understanding.



Simple Touch Sensitive Switch Circuit

We all know about this little versatile chip which finds its way in almost all useful electronic circuits, yes our very own IC 555. The following circuit is no exception, it's a sensitive touch switch circuit using the IC 555.
Here the IC is configured as an monostable multivibrator, in this mode the IC activates its output momentarily by producing a logic high in response to a trigger at its input pin#2.
The momentary activation time period of the output depends on the value of C1 and the setting of VR1.
When the touch switch is touched pin#2 is pulled to a lower logic potential which may be less than 1/3 of Vcc. This instantly reverts the output situation from low to high activating the connected relay driver stage.
This in turn switches ON the load attached with the relay contacts but only for the time until C1 gets fully discharged.

Simple Triac Dimmer Circuit

The circuit of a simple triac light dimmer shown below can be used for dimming incandescent lamps directly from AC mains. The circuit is very easy to construct and uses very few components. The pot is used for controlling the load power or the intensity of the light. The circuit can be also used for controlling ceiling fan speeds.
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.



Simple Water Level Alarm Circuit
Just a couple of transistors are enough for implementing a simple water level alarm circuit and used for getting a warning signal when the water level inside a tank nears the overflowing level. The two transistors are configured as a high gain, high sensitive switch, which also is capable of generating a tone when the shown terminals get bridged through the terminals coming in contact with the water inside the tank. The water offers just about the right resistance value across the specified points of the circuit for initiating high pitched tone or the desired warning alarm.

Simple Temperature Detector Circuit

A very simple temperature indicator circuit can be built using the circuit shown in the diagram. A generally purpose small signal transistor is used here as the sensor and another active device in the form of a1N4148 diode is used for providing a reference level to the sensing operation.The heat source which is to be measured is place in contact with the transistor while the diode is held at a relatively constant ambient temperature level.
As per the setting of the preset P1, if the threshold is crossed by the introduced heat source, the transistor begins to conduct substantially, illuminating the LED and indicating the generation the heat beyond a particular set limit.



Parts List for the above simple transistor hobby circuit
R1 = 1K,
R2 = 2K2,
D1 = 1N4148,
P1 = 300 Ohms,
T1 = BC547
LED = RED 5mm
100 Watt Transistor Based Inverter Circuit


Inverters are devices which have important applications where normal electric supply is not available or difficult to obtain through conventional routes. The simple 100 watt inverter circuit shown here can be built and used for powering many electrical appliances like, lights, soldering iron, heater, fan etc. The whole circuit mainly involves transistors and therefore becomes easier to construct and implement.

Parts List
R1, R4 = 330 Ohms,

R2, R3 = 39K,

R5, R6 = 100 Ohms, 1watt,

C1, C2 = 0.47uF,

D1, D2 = 1N5402

T1, T2 = BC547,

T3, T4 = TIP127,

T5, T6 = 2N3055,
Transformer = 9-0-9V, 10Amp, 220V or 120V

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.

Please refer the article below for the parts list:

http://www.homemade-circuits.com/2012/01/how-to-make-hi-fi-100-watt-amplifier.html

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,
C2 = 100uF/25V
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, T3 = BC547,
T2 = BC557
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.



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  • 278 comments:

    1. Could you tell what is the value of R7 and R8 in the 100 Watt Transistor Based Inverter Circuit?

      Please answer.

      ReplyDelete
      Replies
      1. Good job man. Keep the flags flying. One little observation though, the 100 Watts amplifier seems to be missing a few key resistors. Look at the bases of T10 and T14 and confirm that is exactly what you intended. T14 for instance, the base and emitter are both tied to the negative rail. Similarly, T10 has its base and emitter tied to the positive rail. This configuration is a diode configuration and the circuit will hardly work as an amplifier (being the final stages of the amplifier). I believe you need some resistors there.

        Delete
      2. Thanks very much! I Appreciate your interest.

        Actually The circuit was taken from elecktor electronics magazine and also has been tested by me practically. My prototype worked exceptionally well, so I am a little confused....

        Delete
      3. Yah i w8 your refly because need for my project what the value of R7and R8 in the 100watt transistor base inverter circuit

        Delete
      4. Hi what is the value of R7 andR8 in 100 watt transistor base inverter circuit

        Delete
      5. What volts of capacitor in the transistor inverter

        Delete
    2. Hi swagatam..,
      I need a water level detecting circuit which turn off a relay and the circuit itself when the plastic water tank gets full of water.

      ReplyDelete
      Replies
      1. Hi Vinod,

        Yes we can easily make it by doing a little modification in the circuit shown in the above post.
        I'll try to post the idea soon.

        Delete
      2. Hi good ev sir swagatam what volt of capacitor 0.47uf in 100 watt transistor base inverter

        Delete
    3. Hello..Swagatam..
      40 LED Emergency Light Circuit, How can we add auto cut off Batt. charger circuit and the stepdown transformer 6-0-6 V 500mA it's need to be connected other way round..???

      ReplyDelete
      Replies
      1. Hi PP,

        You will need a separate transformer/rectifier circuit for charging the battery. A low battery cut-off will require another circuit, I will try address a suitable low voltage battery cut off circuit soon through one of my articles.

        Delete
      2. Hello..Swagatam,
        40 LED Emergency Light Circuit
        Thanks for Quick reply..of my query you've replied for first part, The Transformer 0-6v 500mA is connected for LED's to be lit..how much AC Voltage all LED's will get...and backup will be of how much time???
        If you are updating the above mention circuit....Please !!!
        I would like to give it a try...

        Regards

        Delete
      3. ...and what is the value of R2???

        Delete
      4. ...and value of T1..Is it purposely not mention the value of some parts???

        Delete
    4. Hi Swagatam,

      All Simple and useful Circuits.. Thanks a lot, God Bless you.

      MJA

      ReplyDelete
    5. Hello Swagatam..
      Thank you for kind & quick replies..
      Actually in 40 LED emergency Light..the value of T1 and R2 is not mentioned... and I would like this emergency light should be ineffective during day time to save battery power, as I have 12V batt., in the diagram 6V Batt is used...will this same circuit work on 12V Batt.
      I request you to please do needful modification particularly in this circuit diagram...so I can start with it...
      Regards,

      ReplyDelete
      Replies
      1. Hi PP,

        I'll design a new circuit with all these specs soon and inform you when it's posted.

        Regards.

        Delete
      2. This comment has been removed by the author.

        Delete
      3. 0 – 40 V, 0 – 4 Amp Continuously Variable Power SupplyCircuit R4 PLEASE

        Delete
      4. R4 = 0.1 Ohms, 5watts, for 4 amps max.

        Delete
    6. REALLY GOOD CIRCUITS

      ReplyDelete
    7. really cool circuits for a budding hobbyist :D

      ReplyDelete
    8. hello i need the current limiter circuit to operate a sensitive pendulum circuit, so i need some advice with the current limiter circuit

      1) the value of the brown-orange resistor

      2) the reference of the transistors

      3) this circuit can be used to limit a current in a single AA battery?

      is to power up a small electronic pendulum circuit, this was originally designed to work with a 2V solar cell, but when i connect a single AA battery, the circuit is saturated then the pendulum stops moving...

      any help could be appreciated.

      ReplyDelete
      Replies
      1. Hello, thanks for inquiring, however without seeing the application details it will be difficult for me to assess the correct circuit for it, so if you can give me all the technical details about your needs then probably I can help....

        Delete
    9. hello swagatam,
      please update the site with the 5km FM trasmitter and reciver.

      ReplyDelete
      Replies
      1. Hello friend,

        I'll surely do it someday, for the time being you may refer the following link:

        http://electronics-diy.com/tx500.php

        Delete
    10. Hello swagatam,

      what software are you using in drawing your schematic diagrams in electronics? where can i download it?

      By the way, I'm Jeff, my hobby is building simple and useful electronic circuits.

      thanks!

      ReplyDelete
      Replies
      1. Hello Jeff,

        Welcome to my blog!


        I don't use any software, I do it on corel-draw.


        Regards.

        Delete
    11. Hi, Sawagatam,
      I need circuit digram for 3 Volts SMPS

      ReplyDelete
    12. Hi swagatam,
      i do not understand the mechanism through which the circuits operate,although i repaired some faulty things but only through component testing with only 40% of success not knowing what is actually going on in the circuit.Can you please help me to suggest things so that i may learn electronics in detail.
      thanking you.
      sahil sehrayi

      ReplyDelete
      Replies
      1. Hi Sahil,

        I'll try my best to help you in the field....

        Delete
    13. Hi.
      If in automatic day night light switch circuit, number of lights increases, do the value of any of the component changes? n can u please explain how the circuit works?

      ReplyDelete
      Replies
      1. Hi,

        The circuit utilizes a relay whose contacts have no direct connection with the circuit, so the number of lights will not affect the circuit in anyway, you may use any number of lights, but the wattsge shouldn't exceed the max relay contact rating...

        Delete
    14. sir if i use a voltage regulator ic which will provide me a constant 5 volt supply and if i connect two such ic then i will be geting 10 volt supply
      then without using any resistors how many leds can i connect there?

      and will there be any problem in such a cicuit?

      ReplyDelete
    15. No you cannot connect two 7805 ICs for getting 10V, you will have to use 7810 IC for that.

      You can connect 3 LEDs in series without using a resistor in a 10V supply.

      ReplyDelete
      Replies
      1. can i use 23A005 ic for 20 volt productiona dn then connect 6 leds in it!!!

        Delete
      2. 23A005 is NOT a voltage regulator IC, it's a transistor, so you cannot use it.

        Delete
    16. sir can i cnnect a number of leds parallel or series to each other in ac supply directly...........
      if yes hw many leds shall i use and series or parallel?

      ReplyDelete
      Replies
      1. Mains AC is never stable and involves high current, so you can't use LEDs directly on them, they will simply blow of with minor voltage fluctuations.

        Delete
    17. in that water level alarm wats the value of 0.1 ceramic capaeitor?
      is it 0.1 f or 0.1 microfarad

      ReplyDelete
    18. sir in the automatic emergency lamp circuit wats the value of c1

      ReplyDelete
    19. wats the value of d4 and c1 in simple automatic emergency lamp

      ReplyDelete
      Replies
      1. C1 = 474/400V(0.47uF/400V)

        All diodes are 1N4007

        Delete
      2. and the value of t1??

        Delete
      3. can i replace the t1 and t2 with any other transistors in the water level alarm circuit ??

        Delete
      4. sir i asked for that capacitor and the shop owner gave me a capacitor having a written on it as 474kw TL250vE
        is it corrrect?

        Delete
      5. BD140.....or you may also try 8550, 187, or 2N2907

        Delete
      6. all diodes are 1n4007, C1 = 1000uF/25V

        Delete
      7. what is the approximate size of the capacitor?? I am not able to guess from the written value....

        Delete
    20. its about 1.5 cm *1 cm size...
      rectangle type....

      ReplyDelete
      Replies
      1. I think they have provided you with the right part, try it.

        Delete
    21. so i can use a 1000 uF in place of c1??
      and rest all equipments remain the same?
      in the simple automatic emergency lamp

      ReplyDelete
      Replies
      1. I think I am getting confused with the above questions....in LED emergency light circuit C1 = 474/400V or 684/400V and all the diodes are 1n4007

        Delete
      2. okk okk i got u.

        Delete
    22. Hi sir can i know the value of C1 and D4 of Simple Automatic Emergency Lamp Circuit

      ReplyDelete
      Replies
      1. Hi Raja,

        all diodes are 1N4007 and C1 = 0.47uF/400V

        Delete
    23. oh thankq i'll inform u wen i finish that project....

      ReplyDelete
    24. hello sir i successfully done that light... thank u

      ReplyDelete
    25. sir in the simple automatic emergency lamp

      1.sir which terminal of capactior c2 will be connected to diode d1?


      2.which battery sal i use a 9 v 6F22 battery or a 6v 4.5 amp lead acid battery??


      3.if i donot connect the ac supply will there be any problem?
      if no where sal i connect those two free ends

      ReplyDelete
      Replies
      1. longer lead of C2 will go to D1

        use 9V battery only.

        If you do not connect AC, leave the ends free.

        Delete
      2. if i use a 12volt battery??

        Delete
      3. for 12v supply you will have to connect a 330 ohm resistor with each led string.

        Delete
      4. thank u sir!!!
        i hav succesfully completed that circuit!!!

        Delete
      5. That's great....!!!keep it up.

        Delete
    26. Hi Swagat,
      Please post this 100w inverter circuit once again. Because this image is not clear. And i request you to post an inverter circuit with 12v 7Ah battery.

      ReplyDelete
    27. hi swagatam...
      iam making the project on temperature detector ..i want to know
      what source should i use for heating
      and is this circuit working or not???

      ReplyDelete
      Replies
      1. You can use a 40 watt incandescent bulb as the heat source..........the circuit is perfect, it works.

        Delete
      2. thanks...
        but there is a confusion ..the preset use in the circuit is connected with its all three terminals...and as far as i see only last or first two terminals connected in any circuit..
        but in this ckt base is connected with middle one terminal of preset
        is it???

        Delete
      3. It depends on the type of application, here all the three pins are required to be used, otherwise the circuit cannot be set properly.

        Delete
    28. helloo sir..
      can i use bc 547 in water alarm ??

      ReplyDelete
    29. then what model of bjt should i use for t2 because 8550 is not available in the market (near to me)

      ReplyDelete
    30. sir i have made water level circuit
      but when i touch the two wire which are inside the water only then it make sound and it happens in air also
      i use the same component as given above
      can you tell me what is the issue?

      ReplyDelete
      Replies
      1. The circuit will not make any sound if the two wires are not in contact....there must be some leakage in the PCB, keep the capacitor external pin completely isolated from speaker wire.

        Delete
    31. the capacitor is already isolated
      but one modification i have done in the ckt is i used led(positive end with collector of t2 and negative with battery). and it illuminate as i connect the battery.

      ReplyDelete
      Replies
      1. Remove the LED and see what happens, by the way is the speaker producing a buzzing sound...?

        Delete
    32. still getting same problem after removing LED and yes speaker producing buzzing sound

      ReplyDelete
      Replies
      1. If one end of the capacitor remains unconnected the circuit cannot oscillate and buzzing cannot happen, remove the capacitor entirely and now see if the speaker still buzzes or not.

        Delete
    33. Sir Swagatam! in clap switch is there any kind of mic use? or just electret? bcuz i try this circuit using electret but it is not working

      ReplyDelete
      Replies
      1. Hi Bual,

        Yes a condenser mic has been used at the input.

        You will need to connect a small coil also of may be 100 turns of 0.1 mm copper wire across the base of the PNP transistor and positive to make the circuit stable and failproof....

        Delete
      2. sir, gud morning i do the "simple LED music project" but it does'nt work.. i change the dc input to see if there is an output to my project but still the same,, what would i do? i really need your help...

        Delete
      3. Apply music with loud volume and check the voltage at the collector of the first PNP transistor....it should be create peaks equal to the supply votage

        Delete
      4. sir, its me.. the guy asking about the "simple LED music project".. can i used NPN on the first transistor? .. and can i add 5 led lights by making it parallel to each LED light?

        Delete
      5. No an NPN transistor won't work for the input transistor.

        4 LEDs can be added on each channel...

        Delete
      6. Nice site sir Mr. .. Electronic circuits useful ... Congratulations case to you thank you very much for this wonderful work ...Do you find when you electronic circuit measuring humidity? Incubator eggs I want the circuit as easy as I want a metal detector circuit

        With you brother David from Algeria
        Me great honor to get to know you

        Excuse mistakes because I am not the best English
        I relied on the Google translator to talk to you

        tda1558@yahoo.fr

        Delete
      7. Thanks very much David,

        You may refer to the following link which shows an easy relative humidity sensor circuit, you will have to replace the LED with a 0-10V voltmeter or any other suitable type for reading the results:

        http://www.gophoto.it/view.php?i=http://www.electronicdesign.com/files/29/1684/figure_01.gif#.UNlsHuTCbTo

        Delete
    34. Sir Swagatam in the dancing light circuit it is possible to change the bulb in to led? and remove the triac?

      ReplyDelete
      Replies
      1. Hi Bual,

        Yes it is possible, you may connect an LED with resistor across the transistor emitter diode and ground.

        Delete
    35. HI mr swagatam!! a hav a question regarding the LED music light circuit, how and where can we input the music,,?? are the terminals for the speaker indicated in the diagram is for the jack of a cellphone device or something/??
      please reply i need the project urgent!!! THANKS!

      ReplyDelete
      Replies
      1. Yes a cell phone jack output can be used.

        Connect a 47 Ohms resistor in series with the emitter of the first music input transistor for safeguarding it against high pitched music.

        Delete
    36. Hi Swagatam

      Please follow the link below to LTSpice schematic file, showing a flasher circuit:
      https://dl.dropbox.com/u/20969135/Flasher%20OK%20-%20B%20-%20Square.asc

      The simulation is working fine. Even it is working fine with FALSTAD's applet simulator. But when I assembled the components physically, I got constant voltage across "Rload".

      Can you please guide me, what could be the reason.

      ReplyDelete
      Replies
      1. Hi Abu,

        I am not able to see any circuit in the given link.

        Delete
      2. Ah yes, you won't see the circuit there. You will get the netlist of the simulation. Simply go to the file menu and save it and then run it in LTSpice. Or for your convenience, the image of the circuit is attached here

        https://dl.dropbox.com/u/20969135/Flasher.png

        Delete
      3. The circuit should oscillate, try adjusting the value of 470K resistor...use a 470 K pot instead with a 1K series resistor.. adjusting this might help to initiate the flashing action.

        Delete
      4. I have replaced 470K with 500K POT but no result. Only the light turns ON or OFF. Similar result when replaced 330K with 500K POT. :(

        Delete
    37. I tested the circuit with various configurations (different resistors and transistors) on LTSpice and Falstad's applet, the results were positive. One thing I noticed that the 2 transistors should be complimentary of each other. I mean, BC557+BC547 or 2N4403+2N4401 would work, BC557+2N4401 or 2N4403+BC547 would not work. Physically, I have tested with BC558+BC547.

      ReplyDelete
      Replies
      1. If the circuit would work with complementary pairs it would work with non complementary pairs as well, as long as they are NPN/PNP.

        There are many types of similar oscillator circuits on the net, you can try a different, more feasible type of configuration.

        Delete
    38. hello swagatam majumdar,

      i need to build wireless intercom of range 15 meters.
      help me out.

      thank you

      ReplyDelete
      Replies
      1. Presently I don't have one, i'll try to find it, and inform you....

        Delete
    39. hello swagatam,

      please what is the workind operation of
      Simple High and Low Mains Voltage Cut Off Circuit. what functions do the various component perform to carry out the operation. pleae i need your help


      thank u

      ReplyDelete
    40. Sir its me again in Simple LED Music Light Circuit what do you mean by 1k presets? is it a resistor? sorry sir for the disturbance sir im still a beginner

      ReplyDelete
      Replies
      1. 1K preset is a variable resistor whose resistance can be varied by moving its mechanism....

        see it here:

        http://evelta.com/image/cache/data/Other%20Components/1K%20ohm%20Preset%20(Variable%20Resistance)-700x700.jpg

        Delete
      2. is it possible to replace the presets? into a 1k potentiometer?

        Delete
      3. yes it's possible but it would find it hard to keep them stable.

        Delete
      4. 1k ohms resistor? possible or not?

        Delete
      5. do it in this way....connect 1K for the first transistor, 2.2k for the second, 4.7k for the third, 5.6k for the fourth, 6.8k for the fifth and so on....

        Delete
      6. last question sir ! a trimmer is it possible? im very sorry bcuz im sooo annoying

        Delete
      7. By trimmer do you mean a preset? trimmer normally is associated with a variable capacitor which will not work here.....only a variable resistor will work, or do as I have suggested in the earlier comment.

        Delete
      8. sir to the speaker terminal. it requires audio jack it has a three terminal

        Delete
      9. use the big terminal and one of the small terminals.

        Delete
    41. sir, in your fm tx what will b the frequency on which it will transmit?

      ReplyDelete
    42. sir ,one thing more i want 2 know that does this fm Tx require antenna or not ?if it requires then plz tell me location of it.Thanks

      ReplyDelete
      Replies
      1. yes antenna is required, connect a small wire at the collector of the transistor.

        Delete
    43. good day sir, for the Simple LED Music Light Circuit, what is the value of the PNP transistor?i used to do it but it only light the LED. .i used 1K preset. .

      ReplyDelete
    44. SIR please tell me the details of following components in
      Simple Automatic Emergency Lamp Circuit.1. transistor 2. c1 3.watts of resistors.

      ReplyDelete
      Replies
      1. resistors are all 1/4watt, transistor = BD140, C1 = 0.68uF/400V

        Delete
    45. hi swagatam. nice diagrams.. but can u redraw the Simple LED Music Light Circuit with speaker on it?? please..




      mail me pls sir..
      cepada_aj@yahoo.com

      ReplyDelete
      Replies
      1. It won't be feasible presently due to lack of time, but i'll try to do it soon in the near future

        Delete
    46. SIR , CAN YOU DO ADDITIONAL IMPROVEMENTS, I MEAN ADD SOME ADDITIONAL FUNCTIONS TO THE CIRCUIT "Simple Water Level Alarm Circuit", COZ WE ARE ASKED BY OUR INSTRUCTOR TO IMPROVE A CERTAIN CIRCUIT, THANKS IT WOULD BE SUCH A GREAT HELP IF YOU COULD DO IT FOR ME :)

      ReplyDelete
      Replies
      1. I have many interesting water level controller circuits in this blog, just type "water level controller" in the search box, you will find all of them and will be able to choose the best one for you.

        Delete
    47. good day sir! i tried the music led circuit and it is only blinking! what am i supposed to do?

      ReplyDelete
      Replies
      1. adjust the presets so that each subsequent led illuminates at rising levels of the music

        Delete
      2. each presets ? or i will adjust all presets with the same value?

        Delete
      3. each preset a little differently.....

        Delete
    48. what capacitor did you use?a ceramic or an electrolytic?

      ReplyDelete
      Replies
      1. good day swagatam i would like to as for the 100 Watt Transistor Based Inverter Circuit is the output a sine wave?

        Delete
    49. AZIZ.JAMALI@YAHOO.COM
      AZIZ U REHMAN
      GOOD CIRCUIT

      ReplyDelete
    50. Hi swagatm
      Pls tell me, which typr of transistors are used in "Timer Circuit with Independent On and OFF Delay Adjust Facility"

      ReplyDelete
      Replies
      1. Hi Zia,

        the transistor numbers are given in the diagram.

        Delete
    51. hello ! bro
      Thanks for what you done for whole circuits i am an engineering student ..........i want a different project from all which can impress my teacher well...........to get max marks i need some more information .............

      ReplyDelete
    52. hi swagatam, in the 100 Watt Transistor Based Inverter Circuit is the output a sine wave?

      ReplyDelete
    53. thank you! another question swagatam, is the output of this inverter can reach 60Hz?

      ReplyDelete
    54. yes it can be done by setting the capacitor values appropriately.

      ReplyDelete
    55. what did you mean by setting the capacitor values appropriately?i will change the value of the capacitor the you gave in the parts list?what type of capacitor will i use?mylar?is the TIP there is an oscillator?

      ReplyDelete
      Replies
      1. calculate the capacitors appropriately which would provide you 60Hz....refer to this link to know more:

        http://www.electronics-tutorials.ws/waveforms/astable.html

        Delete
      2. tnx swagatam, in the site that you've given, is it possible that we will not change the value of capacitor but rather change the value of resistor?by the way, what is the value of R7 and R8 in the circuit?

        Delete
      3. excuse me sir swagatam, is the blue line in the 100w transistor based inverter is the positive?

        Delete
      4. transistor base resistors can be changed instead of the caps.

        R7, R8 = 22 ohm/ 5 watt

        Delete
      5. what capacitor should we use?mylar or electrolytic?if electrolytic what is the positive and negative side their?

        Delete
    56. How to use TL2N2219A TRANSISTOR in Wireless Microphone Circuit.

      ReplyDelete
    57. i would like to know the value of P1 and P2 on 0-40 volts/0-4 amps adjustable power supply... thanks in advnce

      ReplyDelete
      Replies
      1. please refer to the following post:

        http://homemadecircuitsandschematics.blogspot.in/2012/01/how-to-make-versatile-variable-voltage.html

        Delete
    58. Can U please let us know the values. Of capacitor c1 and diode d2 in the circuit simple emergency flashlight

      ReplyDelete
    59. Hi
      Let i want to know about simple electronic circuit creating application for my windows 7

      ReplyDelete
    60. hi
      can you tell me how all the components work in simple automatic emergency lamp circuit?

      ReplyDelete
    61. good day sir! do you have a fm transmitter circuit with a 30 to 60 meter range?

      ReplyDelete
      Replies
      1. search for "wireless speaker" in the search box, the relevant circuit will provide that much range....

        Delete
    62. Hi mr. / swagatam what is the volt of 0.47uf in the circuit 100 watt inverter

      ReplyDelete
      Replies
      1. Sir what polarity in R5and R6 negative or positve

        Delete
      2. R5 R6 are resistors and resistors don't have polarities.

        Delete
      3. I mean sir in 100 watt transistor base inverter
        what polaritie of 0.47uf cap. They can top to R5 and R6 . Positive/ negtive.?

        2nd quiz.
        What type of transistor T4 ,T5 PNP or NPN they can buy.,if sold out to the market transistor # TIP 127 what transistor they.?

        Delete
      4. Please refer to this post, you will get a better picture of the design:

        http://homemadecircuitsandschematics.blogspot.in/2012/07/simplest-and-best-100-watt-inverter.html

        0.47 is a non polar cap.

        use BD680 in place of tip1237, they a PNP transistors.

        Delete
    63. ,.good evening,sir! i just want to ask for help. i'm needing for a simple circuit that uses a sensor, which we can use in everyday living, yet the materials are affordable. hope you will respond! thanks in advance! :)

      ReplyDelete
      Replies
      1. what kind of sensor are you looking for? Please provide more details about it.

        Delete
      2. ,.any sensor will do,sir! ahm, is there any "plastic materials sensor" sir? i just thought of a circuit which can separate wastes (biodegradable from non-biodegradable)... is this possible? can you help me create a circuit like this? thankyou soooo much,sir! good day! :)

        Delete
      3. I am sorry, Such a circuit would be difficult to design at my level, because there's no sensing element available in the market specified for distinguishing biodegradable from non-biodegradable

        Delete
      4. you are welcome Zenilyn, keep posting.

        Delete
    64. Hai sir
      I have a 6v 4.5ah lead acid battery.then what are the changes reqierd the automatic emergency light circuit

      ReplyDelete
      Replies
      1. Remove D3, D4 and connect the battery directly to the shown position, no changes would be required.

        Delete
    65. Could someone post a battery eliminator circuit.
      I need to eliminate 2 AA cells which would be 3.0Vdc with clean DC power.
      It is in an audio circuit so no ripple. I suppose I could try a wall wart DC power supply, but I would want to make sure it is good clean DC so no ripple is injected as it is an RTA device.

      ReplyDelete
    66. hi I am Shadab , I think you remembered me.
      I have got a science congress in my school so, I was searching for non polluting batteries just like air battery, earth battery etc.
      Do you have any other type of battery or do you have any capacitor related project or circuit as battery.
      please please..........


      thankx

      ReplyDelete
      Replies
      1. I am sorry, presently I do not have any info regarding such batteries.

        Delete
    67. hello sir , i want circuit which can run a single DC motor in clockwise and anticlockwise direction......also i want to know which type of relay should be used in toy car for movt left and right......

      ReplyDelete
      Replies
      1. It's not just about relay, it's much more complex, you can refer to this post:

        http://homemadecircuitsandschematics.blogspot.in/2012/09/make-remote-controlled-toy-car-circuit.html

        Delete
    68. value of R2 missing in 40 LED EMERGENCY Light

      ReplyDelete
    69. in "Automatic Day Night Light Switch Circuit" please tell me the wattage of the resistors, thanks

      ReplyDelete
    70. can i have working of emergency lamp ckt

      ReplyDelete
    71. can i ve working of emergency lamp ckt ?

      ReplyDelete
    72. Sir, what will be the wattage of resistor for 5 A maximum load current in the current control circuit ???? Will this circuit be able to handle such high load???

      ReplyDelete
    73. Sir for the 'SIMPLE CURRENT LIMITER CIRCUIT USING 2 TRANSISTORS' which you had posted here. I want a quick reply sir

      ReplyDelete
      Replies
      1. You can refer to this post and calculate yourself as per the given formulas at the end of the page:

        http://homemadecircuitsandschematics.blogspot.in/2011/12/make-hundred-watt-led-floodlight.html

        Delete
    74. good day sir!

      I have a question for you.

      1. Is the transformer 's secondary a 6-0-6v or a 3-0-3v

      2. what is value of R1

      ReplyDelete

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