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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:


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.


  1. 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..???

  2. 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…

  3. 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.

    • 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….

  4. 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.


  5. 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

  6. 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?

    • 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…

  7. 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?

  8. 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.

  9. 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?

  10. 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

  11. 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???

    • 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???

  12. 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?

    • 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.

  13. 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.

    • 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.

    • 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….

    • 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…

    • 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?

    • 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


  14. 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!

    • 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.

  15. 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.

    • 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.

  16. 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

  17. 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. .

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


    • 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.

  20. 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 ………….

  21. 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?

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

  23. ,.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! 🙂

  24. 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.

  25. 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……….


  26. 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……

  27. 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???

  28. how about in "Simple Audio Power Amplifier Circuit"?

    1. what is the transformer, 12-0-12v or 6-0-6v?

    2.in 100E 5WATTS, what does "E" stands for?

    3. Can I use a speaker with
    impedance: 4 ohms
    rated input: 1.6 watts?

    by the way thanks for all the answer you gave me!!!!!!!your the man!!!!!!!!!!!! 🙂

  29. Hi Swagatam

    I want to use the current limiting circuit with a car battery, to provide fixed 5A to a load which can draw more current. Are the following values okay?

    Q1 = TIP32C
    Q2 = TIP127
    Base resistor = 1k
    Current resistor = 0.14 (wattage ?)

  30. Hi swagatham,

    Its me Nithin from kerala , iam planning to build a simple circuit for my water tank which always overflows and makes wastage of water, i need a circuit which can trip the pump circuit main after the water level attains.so please help me to do this task by guiding me.also please provide a power supply circuit also.thanking u

  31. hii swagatam, i want ask about emergency lamp using Led, when we use a battery 6v 4.5ah as battery, zener 12v needed change / lower it ?? would it damage battery 6v ???

  32. Hey Sir!
    We have this project at school and there should be a triac in it. I found your music operated dancing light circuit to be interesting. Uhm does it really work sir? Also can I change the lamps into LEDs, without getting rid of the triacs? Lastly, what is the wattage of the resistors?

    • Hi Carmichael, yes it will work if built correctly as per the diagram…make sure to connect a 1k resistor in series with the music input capacitor at the PNP base.

      The circuit is not isolated from mains so is highly dangerous to touch in switched ON position.

      all resistors are 1/4 watt rated

      LEDs can be used but using LEDs will make the purpose of the triacs useless

  33. Hello Sir, I would like to know how I can adapt the simple current limiting circuit using two transistors for my application. I would like to connect this circuit between my main power supply and load. My main power supply is 115Vac to 230Vac. My load is 115Vac to 230Vac at 10watts. I want this circuit to disconnect the load if the load exceeds 10watts and reconnect if the load is 10watts or bellow. Please assist me with components specifications as well as what changes will I need to make if I want to change the value at which the disconnection takes place. Kind regards.

  34. Hi Swagatam,

    Iam from Indonesia…..
    I Need Schematics For Incubator Timer with Hight Torque Motor ( DC Motor Power Window in Car).
    I am trying to get a DC motor to run in two direction until it reaches the end position then stop and switch polarity so it will run the other direction when power is reapplied.
    Then do the same thing at the other end.

    1. timer turns power on for 1min. (7:00am -7:01am)
    2. motor runs in one direction until it hits stop position, say 30sec.
    3. power to motor turns off when it hits stop position and delays for the 1min. timer to end/turn off main power. also reverses polarity so that.
    4. next time the main timer comes on (10:00-10:01) it dose the same thing in reverse direction and repeating continuosly
    5. 12 VDC Motor Reverse (Just two cable from motor + and -)
    6. Need Led Indicator for Rev/Fwd motor

    Can you Help me Sir and Please E-mail Schematics to : jakarta_anwar@yahoo.com

    Thank you in advance for any help. This is an important home project that needs to be 100% reliable.

    • Hi Anwar,

      The 1 min timer is not required since the stop switch will automatically reset the timer after 30sec…..the frequency timing between 7 to 10 is important…the timer has to initiate after this period each time the motor has finished its operations.

      I'll try to post it in the blog….stay tuned.

  35. Hi, I was wanting to attempt to construct your LED light show circuit. The image says all transistors are BC547B transistors, does this include the PNP transistor that is attached to the speaker terminals?

    I was also wondering if I could use a 3.5 audio jack instead of the speaker terminals and any ideas on how to go about doing that? I would love to exchange emails about this if you're available.

  36. Hie sir
    I have tried making timmer circuit with independant on off delay adjust fecility,its just not working,i want a2.4 v bulb with 9 v batterie to be onn for 2 sec and off for 15 to 30 sec adjustable can u plez help me…. thznx

    • Hi, the circuit will surely work….connect another BC547 with the lower transistor to make it a Darlington pair, this will improve the circuit response…

      how can you use a 9V battery to drive a 2.4V bulb?….both the voltage levels must match..

  37. Good Morning Engr. Swagatam!
    I just want to ask about the:

    40 LED Emergency Light Circuit section

    Can you give me the specific rating of each parts if I have a:

    A transformer rated @ 1A; 15v-0v-15v on sec.; and 0v-110v-220v on pri.?

    And instead of 12v supply make it 5v dc?

    And the rating of the output transformer as follows: Vout > 12V
    e.g. 13v and above.



    • Good Morning Eshkariel,

      the supply needs to be equal to the transformer winding voltage rating, otherwise the output will be much lower, what's your battery AH specs?….actually the transformer is simply not required….you can connect the LEDs directly with the battery in parallel strings.

  38. Referring to the phrase:

    "actually the transformer is simply not required….you can connect the LEDs directly with the battery in parallel strings."

    What I have is a hand crank generator using a dc motor. It produces voltage of about 9v max and a current of 50mA max. My
    plan is to use the circuit of "40 LED Emergency Light Circuit" section which would invert the 9v dc to >12v ac and then
    rectify it to make it dc again and then regulate it using a 12v regulator and replace it in place of a 12v battery in a UPS.

    Would that work?

    I appreciate your answer a lot.

    thanks a lot!!!


    As soon as it works, I will connect the hand crank generator to a stirling engine to make it automatic, replacing manual human power with autmatic heat engine power.

    Next problem: How to make a high torque Stirling engine…XD…but that's out of your field of interest…so i'll take it on my own..btw…thanks again!

    • sorry that would never work? you should have specified this before.

      moreover as per the diagram the trafo needs to have 220V winding at the LEd side for illuminating 40 LEDs….

  39. hellow sir! I am an electrical student, here in the Philippines and i know you are helpful. Im developing a device for my thesis,please help me. my problem is schematic diagram of an AUTOMATIC MIST IRRIGATION FOR MUSHROOM PRODUCTION which the objective is when it set 25 degree celcius and its attain the temperature, the irrigation will turn it ON. we are insufficient of materials here so a low cost of materials to be use sir. Im hoping for your immediate response sir because I have only less than a month free to do that thing. thank you for your anticipation.

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