A practical electronics engineering resource focused on tested circuit projects, clear theory explanations, design calculations and real world troubleshooting support for students, hobbyists, and professionals.
Questions Answered with Practical Working Solutions
Backed by more than two decades of hands on circuit design experience, reader questions posted in the comments are reviewed and answered personally. Wherever necessary, circuit corrections, design improvements, and verified working solutions are provided to ensure accuracy and reliability.
How To Use This Website
- Start with the Electronics Tutorials section if you are new to circuit design.
- Explore application based projects to find ready to use circuits.
- Read the comments for practical tips, corrections, and reader discussions.
- Post your questions to get guidance and improvements where needed.
Learn Electronics Step By Step
Electronics Tutorials
Foundational tutorials explaining electronic concepts, calculations, and working principles in a simple and practical way.
Semiconductor Theory
Detailed explanations of semiconductor devices and circuit theory with practical examples and applications.
Arduino and Microcontrollers
Arduino programming tutorials and microcontroller based automation projects with complete circuit details.
IC 555 Timer Circuits
Classic and modern IC 555 timer circuits explained with calculations, diagrams, and application ideas.
Power Electronics and Energy Systems
Inverter Circuits
Designs that convert DC power into 220V AC with explanations ranging from basic to advanced sine wave systems.
Battery Charger Circuits
Controlled battery charging circuits covering lead acid, lithium, and industrial battery systems.
Power Supply Circuits
Fixed and variable voltage power supply projects for workbench testing and embedded applications.
Solar Controllers
Solar charge controllers and renewable energy projects using PWM, MPPT, and microcontroller techniques.
Application Based Electronic Projects
Home Electrical Projects
Electronic circuits designed to enhance safety, automation, and efficiency in home electrical systems.
Industrial Electronics
Control and automation circuits used in industrial machinery and process systems.
Automobile Electronics
Automotive electronic projects for lighting, safety, and performance enhancements.
Motor Control Projects
Speed and torque control circuits for DC and AC motors used in home and industrial applications.
LED and Lighting Projects
Decorative and functional LED lighting circuits including dimmers, chasers, and drivers.
Remote Control Circuits
Wireless and IR remote control circuits for convenient device operation from a distance.
Specialized and Utility Circuits
Wireless and GSM Projects
Wireless control and GSM based communication projects for monitoring and automation.
Meters and Testers
Hand-built electronic meters and testers useful for diagnostics and troubleshooting.
Timer and Relay Circuits
Delay timers and relay switching circuits for automation and protection applications.
Learning Through Discussion
A lot of the circuits here slowly get better through questions and discussions in the comments. Readers point out real world problems, ask for small changes, or request clarifications, and over time this back and forth helps turn the designs into more reliable and practical working circuits.
Try and Test Circuits Online
To help readers better understand how circuits behave, this website also includes a simple online circuit simulator. It can be used to visualize basic circuit operation, test component changes and explore circuit behavior before building it practically.
Recent Community Discussions
Latest questions, answers, and circuit improvements discussed by readers and the author.
Yes, that's correct!!
The VGS(th) parameter of IRF540 is "minimum: 2.0V; maximum: 4.0V (conditions: VDS = VGS, ID = 250 μA)". Does this…
You just have to follow the instructions as given in the diagram...just connect those points as given in the diagram...the…
Hi, I think it would be easier to build a current triggered cut-off, that detects amps and then cuts-off charging…
Then how do you install it on the IC, sir? Can you give a picture example? https://www.homemade-circuits.com/wp-content/uploads/2026/06/add-voltage-regulation-output-via-optocoupler-and-TL431-feedback-e1782724372274.jpg
Common Problems Addressed
- Circuits that do not work as expected after assembly.
- Confusion about component values and calculations.
- Improper power supply or overload issues.
- Noise, heating, and instability in practical circuits.
- Modification of existing circuits for custom requirements.
Note: All circuits are provided for educational and experimental purposes. Readers are advised to follow proper safety precautions while working with mains voltage and high power circuits.
Questions & Answers
please let me join and get your projects
I would like to know the values of R 45 and R 49 in Microtek VO 3.32 UPS board. In one circuit diagram it is 100K ohm both. Installed resistors in my board are 47 ohm each.Thank you.
Sorry, I do not have sufficient information regarding your question at this moment.
Thank you very much!
Good morning, I’m Carlos Velazquez. I hope you are in good health.
I’m trying to make a circuit that illuminates a painting at night for 14 hours. Starting at 6:00 p.m. and turning off at 8:00 hrs. The lighting is with LED, it must be activated with LDR when capturing the darkness outside and sending a signal with RF 433mhz and turned off when capturing the light by sending a signal to the receiver.
The transmitter must be outside the house powered by a solar cell that recharges a battery that does not consume much current and inside the receiver with a rechargeable battery, this process is daily.
For your attention, I thank you for your time and support.
Good Morning Carlos,
I will design the circuit and post it as a new article. Once it is done I will let you know.
Hi, how is LED lamp powered? Is it through a chargeable battery or from an AC outlet indoors. If AC outlet is available indoors then the receiver battery can be also charged through this AC source.
Yes, it is a rechargeable battery that is inside the house, could you suggest which battery to use? Thank you for your time
The battery voltage and Ah specifications will depend on the LED specifications. If you tell me the LED specifications, I can figure out the battery specifications.
How would you charge this battery, is it through the home AC outlet or through a solar panel?
Disculpe, no encuentro mi comentario donde lo podre encontrar y verificar el favor que le pedí.
The comment might have disappeared for you maybe due to the automatic clearing of the site cache, but no worries, I have received your comment and will try to design it soon.
I’m Chibueze Nwakpuda from Nigeria, a regular follower of your blog. Please sir, I am experiencing difficulty in building electric stove using plaster of Paris (poo) as my element base. The pop cracks when heated. Kindly advise me on the substance I can place my heating spring coil element on that cannot crack.
Thank you.
Hi Chibueze, Sorry, I have no idea how the Pop cracking problem can be solved, it is beyond the scope of my expertise.
Good afternoon, regarding the LEDs, I did a test with 6 LEDs but I need more light, so I ask your suggestion which would be the ideal one and regarding the battery, as you told me, it can be either solar or AC rechargeable.
I thank you for your attention and support of this important project for me. Thank you.
It will be difficult for me to know how much light you need for the painting. It will depend on the size of the painting, and the number of paintings.
If 6 LEDs are not enough, you can try 10 LEDs.
I will also need to know the specifications of the LEDs you are using (Voltage and current rating)
The LEDs are 3.4 v, 20 mA white, it is only 1 square of 44 x 60 cm. Thank you.
OK, I have designed the circuit, you can find the post in the following link:
https://www.homemade-circuits.com/automatic-night-activated-wireless-light-circuit-for-paintings/
I have simple mosfet wire loop security device but there is an issue the thieves can can joint the loop before the protected gadget thus making the system normal and steal the protected gadget can you design a wire loop circuit such that it activates alarm on both cutting and jointing the loop
Please i will be very thankful
Hi Swasti,
If the intruder already knows the location of the trip wire and manually fixes it then there’s nothing we can do. The trip wire or the loop wire is supposed to be hidden from the intruder, if it is visible or known to the intruder then it is impossible for it to work effectively. In that case better to install a simple PIR based alarm circuit or a motion detector alarm circuit.
Thank you sir
Yes sir i have considered pir based alarm and think but In my case there in the protected area sometimes animals like dogs and cats are walking so it is possible that most of the times my PIR based alarm will give false alarms therefore it is failed
Kindly if you have another idea or circuit then please guide me i need your support please
Hi Swasti,
Yes, PIR sensor or any other motion sensor will detect animals also and give false alarm, which cannot be avoided.
I think a vibration sensor can be the best option in that case, which will detect strong vibrations if an attempt is made to remove the solar panels from their installations.
Let me know your thoughts on this.
Sir you are the expert if you consider it helpful then i will be waiting for the circuit diagram of vibration sensor please make i perfect diagram so that i make the device soon
I appreciate ?
Thank you Swasti,
According to me the first circuit from the following article will be most suitable for you:
https://www.homemade-circuits.com/simplest-sound-activated-relay-switch/
You can reduce the sensitivity of the MIC simply by increasing the value of R1 to 10k or 22k or 33k.
You can enclose the whole circuit in a plastic box and clamp it with your solar panels. If anybody tries to remove the solar panels or tries to tamper with the circuit box, the relay will be instantly activated causing the alarm to sound.
If you want more information about the circuit details or the construction you can comment under the above linked article post, I will try to sort it out for you.
I find this site very educational, thank you Swagatam and everyone.
I have the a need for the following device. Would be grateful for your help in building it.
—————————-
Light trap for Insects : the device turns on LED light automatically at dusk for 2-4 hours and attracts harmful insects in a crop field.
Device should not overcharge the battery, nor allow it to be depleted below a certain level to extend battery life.
Device should have a switch to manually turn the lights on and off.
The device should use low cost components since I need to deploy many of these devices.
The device should be essentially weather proof as it will be deployed in open field.
Thank you in advance for your help!
Thank you OP,
I will try to design the circuit soon, and let you know once it is done.
Thank you Swagatam, truly appreciate your help in this regard.
Thank you OP, I have published the article, you can find it under the following link:
https://www.homemade-circuits.com/insect-light-trap-circuit-for-protecting-crops/
Pls can I see some of this components to buy in Nigeria
Hi boss, thanks for the circuit diagram. But I have some issues. 1, I don’t understand what kind of dieyot is D3 and I can find 48volt relay, is there any resistor I can use to convert it to either 12or 24volt relay. 2, which of the virable resistors is responsible for setting the low voltage level. Like if I want the relay to come or at either 50,40 or 30 percent. Thanks for all your response.
Hi Jolly, which circuit are you referring to? Please reply under the same comment so that I can refer to the circuit diagram.
The 48volts monitoring relay circuit
Sorry I cant find the original post where you posted you previous question.
Hi, I can’t find it either. But I received a circuit diagram for the 48volts battery monitoring relay. The idea was that the system is a 48volts system. The device was to monitor the 48volts when the voltage get low to like 30 or 40 percent a relay on the monitoring device should switch on and when the battery goes to full level the relay should switch off. I got a circuit diagram from you today about it but there are some things I’ll want to to look into on the drawing.
Your initial question was posted under the following article. Please ask it under the same thread, I will try to help:
https://www.homemade-circuits.com/3-step-dc-voltage-level-monitor/
I have a relatively high impedance voltage source that puts out +/- 200 mV depending on the pH of the solution it is exposed to. I would like to have a simple op-amp based circuit that would apply a opposing voltage to this device such that net zero current flows. I would be monitoring the opposing voltage. The overall impedance is of the order of 1 MOhm, so the short circuit current otherwise will be in nanoamps. So the need is for a zero current, constant current circuit…
Your thoughts are most appreciated…
As per my understanding, you want another 200mV DC source through an opamp that could be connected with your existing 200mV?
Please let me know if I understood it correctly.
Yes basically so. It will end up applying exactly negative of the voltage the exiting probe is generating, in the extreme +/- 450 mV.
Sorry, I am still having problems understanding the configuration.
Do you want to sink the existing 200mV source to GROUND?
This can be done by shunting the source to ground with a jumper, what is the role of the op amp supposed to be here?
HI
is there a component tester for intergrated ccts eg LM386 ?
Hi, the easiest way to test the IC is by building its basic configuration as shown below:
The pot is not required. Simply touching the pin#3 directly should cause the speaker to generate a loud buzzing sound, indicating a good IC.
Hi, I’m Albrecht.
I’m looking around for a low noise amplifier for very tiny amounts of charge. For low low noise reasons I consider to use an Agilent ATF-55143, Although this device is made for rather high frequency applications in my case the required frequency band is more like “DC”, i.e. 10kHz up to 3MHz. Are there somewhere advices how to bias in an optimal way the pHEMT in order to get the maximum S/B ratio?
Hello Albrecht,
Did you check its datasheet, I can see some related information being available at the bottom section of the datasheet.
https://www.farnell.com/datasheets/33952.pdf
lm386 is running very hot very hot to touch is this normal?
It is not normal, how much supply voltage did you use? Try with 5V first then try 9V.
Hi sir..I want to build a personal website filled with my personal electronics design interests and wish to build my skills with a dedicated storage space organized neatly.So please help me on how to create website like yours.
Hi Girish,
You can create and manage a website cheaply on a WordPress platform.
Learning WordPress is a comprehensive process and can take many months to master. However as far the initial setup is concerned, you don’t have to worry at all, since it will be done by your hosting provider. You can also take their help to further learn regarding how to optimize your WordPress site. Go for hosting provider who offer the best SSD storage with litespeed cache, compare the plans and select which you find the most economical.
Hi All,
I am needing a small circuit that runs a motor for exactly 3 rotations.
Wondering the best way to achieve this? The start needs to be triggered by a random input from a light that will go on and then off and the rotations are independent of the light being on – so there is a separate power source for the motor which supplies the motor.
I am thinking if possible, the light triggers the closure of the motor circuit starting the motor. An optical interrupter then closes three separate transistor switched circuits. When the 3rd circuit is closed, this then opens the motor circuit. This should also ignore any subsequent trigger events while operating so I am guessing the circuit from the trigger source (light) needs to be open between the motor being triggered and stopping.
Hope this makes some sense. Getting back in to all this so pardon any odd explanations. Thanks
Michael
Hi, thanks for the question.
I guess the light needs to remain ON until the 3 rotations are completed by the motor, otherwise, in the absence of light the opto-interrupter might not be able to sustain the triggers for the 3 transistor switches?
Please Let me know if I am correct.
Thanks for the prompt response. I should clarify that the light is external to this design. It is a merely an intermittent light that I need to use as a trigger only. It is intended that the motor will have a disc with a “tag” which passes through the opto-interrupter with each rotation. So each time the opto is opened/closed it needs to do something so that on the third rotation it shuts off the motor. Hopefully that helps.
Seems like my last reply didn’t make it to the thread.
Thanks for the prompt reply. The light is essentially the trigger to start the motor. Its circuit provides the input to the motor circuit. So when the light flashes the motor needs to turn 3 times even though the light circuit is off. So the motor has its own power and its circuit is closed when the light flashes and opens after three rotations. The motor has a disc with a small plate that passes through the opto. I am thinking that this could be used to eventually open the motor power circuit on the 3rd rotation. Hopefully this makes it a little clearer.
Thanks for the clarification.
Your last reply was also received and posted.
Ok, the external light is only for the initial triggering for the motor.
That means the opto-interrupter should be having its own light, such as an LED for implementing the switching actions, right?
If yes, then i think the whole operation (until switch off after 3rd rotation) can be implemented using a 4017 IC.
Thanks so much for the lead. I have read up on the 4017IC and agree that it looks promising. Another question is that the specs talk about CLOCK pulses and it identifies the use of the 555 IC. Is this because of the shape of the pulse? Or could the opto to just pass the positive charge to PIN14? Or do you think I should use the opto to trigger the 555 IC to send a CLOCK pulse?
I think the opto can be directly configured with pin#14 of the IC 4017 and will work well, no need of employing a 555 monostable in the middle.
This leads to another question … the opto is essentially always on (correct?) so when the “cam” passes through the opto it will close the circuit on the collector side of the opto. Closing that circuit then provides the pulse for PIN#14 on 4017IC. Have I got this right?
You are absolutely right. You can also reverse the action by connecting the emitter side of the opto transistor with pin14. A resistor of around 100k will need to be connected between pin14 and ground.
I have run into a small problem … The external light flashes and that raises the voltage at the base of the NPN transistor which closes the circuit to start the motor. Correct so far? The problem (afaik) is that circuit will open when the base voltage drops and the motor will stop. I have worked out the 4017IC usage to count 3 turns and then stop. The motor is geared down to roughly 1 rev per sec. How do I keep the motor circuit closed after the initiating flash?
I think the following circuit should be able to solve the problem:
Make sure to replace the BC557 with TIP127 (or as per the current rating of your motor) and you can alter the values of the 470uF and the 22k resistor to adjust the delay OFF time as required.
Thanks for your help with this. So I now have an opto-controlled circuit working well on a 5V circuit divided from a 9V battery. I need to turn the motor on and off from the collector of the opto. It works fine for an LED but not for the motor which needs >7V (the LED is getting approximately 1.5V). I am guessing here that I use a diode to the base of an NPN transistor to open and close the higher voltage circuit that the motor is on? If so, how do I get this to work as the transistor does not seem to be switching … its always on at the moment. If there is another way to do this, what would your suggestion be? Thanks
Can you please tell me which opto-coupler you have used? And also please provide the voltage and current specifications of the motor. I will try to solve it for you.
The opto is ZD1901 (Vf = 1 to 1.3) I am seeing 1.95V at the collector. The motor specs are here 55RPM 12VDC Reversible Gearhead Motor | Jaycar Electronics. Thanks. Appreciate your help.
Thanks for the information.
The opto transistor will not be able to handle the motor directly, since the motor is too heavy for the opto transistor.
Could you please explain how do you wish to configure the motor with the opto-interruptor?
Please explain the working of the configuration in short.
The opto-interrupter circuit needs to work on a 5V circuit so I am just using it to switch on and off. The motor needs to run off a 6 to 12V circuit so I am thinking it will be on a separate circuit which is switched on and off by a transistor with diodes connected to the collector??
You can try one of the methods explained in the following article:
https://www.homemade-circuits.com/how-to-drive-relay-through-opto-coupler/
The relay coil can be replaced by your motor. The 1N4007 will remain as is, parallel to the motor connections.
Let me know if you have any further doubts.
I must be doing something wrong but have checked it a few times. I have dropped the need for the 5V input so I have the 9V available for the motor. On my breadboard I have the opto switching correctly to turn the LED on/off but there is nowhere to get the 9V for the motor or the current for the motor to operate in line with the opto (like the LED).
You can try the following configuration:
When the LED light is unobstructed, the motor is ON. When the LED light is obstructed the Motor is OFF.
Thank you very much. Works well!
Now I have to circle back a bit. I need to change the voltage up to 12V which will be fine. This motor control needs to be triggered by a 5V “pulse” (a light on/off cycle). It needs to run independently of the trigger circuit until the opto is obstructed. This time I am guessing I need an NPN before the motor where the base is on the triggering circuit… but the base will need to stay high until the opto is obstructed. So it will need to connect with the opto collector? Is this right?
Thanks for your feedback, however I have some confusions.
In the following figure, the motor will start running as soon the +9V (or +12V) is applied to the circuit.
So what modifications do you want to have in the following design so that motor can be triggered by an external 5V “pulse” (a light on/off cycle), and it runs independently of the trigger circuit until the opto is obstructed.
The circuit you suggested is good. So I guess the concept I am chasing is for this circuit to always be open unless it is triggered by a 5V light getting a pulse so it flashes. This flash then closes the motor circuit which remains closed until the opto is interrupted and it switches off the motor AND opens the motor circuit again. So power is always available to the motor circuit. But the motor is effectively switched on by the flash going off and switched off by the opto being interrupted.
Hope this helps
So where do we connect the opto interrupter LED in the previous circuit? Do we connect it with the 5v pulse?
I think that circuit from the motor input to the TIP output is good. Between the +9V and the motor needs to be open until the 5V flash pulse so I am guessing an NPN with the base going high from the 5V pulse. But it will also need to stay high until the opto is interrupted. So this “motor circuit” is closed by the 5V pulse and opened by the opto.
Ok, so I think you can try the following circuit:
Nice. Thanks for this… basically there. I noticed the control is not necessarily based on the opto though. I increased the capacitor to 470uF which gives me almost 3 rotations of the motor which is excellent. I also found that the pulse does not restart the motor as the cam on the motor remains over the LED opto. I have fixed this by connecting the motor directly to the incoming pulse which just moves the cam enough to clear the opto slot and then the motor circuit is closed and it runs until the cam comes around again. So this is exactly what I was after. Thanks for your assistance with this. Much appreciated.
Thanks for updating the results. Glad it worked. All the best to you!
Apologies but I spoke too soon. All good with what I have now it’s working. The other issue is that the whole circuit needs to ignore the input pulse from the flash for at least 30 seconds after the opto is interrupted. So I was thinking this could be done using some arrangement with the 4017IC you had mentioned in an earlier message. Or is there a simpler option?
Thanks
No problem, it can be designed using the IC 4017 and a small 30 second, however this idea may work consistently only if the IC 4017 circuit is allowed to reset after the 30 second period.
One more thing, If the input voltage was changed to 12V, should any of the components be changed for the higher voltage? The motor is rated 9-12V.
Nothing needs to be changed in the previous circuit for a 12V supply, all the parts can remain as is.
Thanks. 12V is much better. After reviewing what is going on electronically and mechanically, what would be the best way to open the circuit at the pulse while the opto is unobstructed? would it be feasible to use a PNP transistor across the pulse input and 33K resistor. Would the base be connected to the TIP emitter?
But the circuit or the motor is supposed to close (switch ON) when the input pulse arrives, right?
By “open” do you mean turn OFF?
I am not able to understand the new working.
Please elaborate a little.
Yes, a PNP can be used a switch to toggle the input pulse, between the input pulse source and the 33k. Emitter towards the (+) pulse source.
Switch ON scenario is correct. Yes I mean the circuit is open so its OFF. Now looking at it in its operating environment, I need the motor circuit to “ignore” all pulses UNTIL it is switched OFF when the opto is interrupted. When I am testing it I can send a pulse as many times as I like and the motor keeps turning. I am having difficulty deciding how to ignore the pulses – either using the 4017IC to set a “lock-out” period or to do something which ignores the pulses as mentioned above.
Yes, the 4017 can be used to ignore the pulses. This can be set depending on the number of rotations for which the pulses need to be ignored.
So using two 4017 I can keep the base on the PNP transistor high for say 30s? Then reset the first 4017 at pin 15 from pin 7 on the 2nd 4017, correct? The timer circuit would also be closed (ON) with the first pulse and then it should ignore additional pulses for 30 seconds. Does that seem correct? Thanks
Hello, is there any way or idea to prevent solar PV from feeding power back to the grid?
Hello, to understand he issue better, please explain how the system is operated and connected with the grid, if possible provide a schematic.
My inquiry is about PV systems connected to the grid. Is there a circuit or relay that doesn’t allow the system to feed into the grid?
I do not have a ready circuit idea which can do this. However, if you show me the full PV diagram then maybe I can design one.
I apologize, but I am not able to provide you with instructions on how to sketch here.
In that case it might be difficult for me to provide a possible solution.
Bill
i seem to have lost the reply and schematic that you sent me. Could you advise on how to get it back
Hello Colin,
You can find our recent discussions under the following article:
https://www.homemade-circuits.com/simple-delay-timer-circuits-explained/#comment-151751
I want some help regarding my PCB. How can I contact you directly
I am sorry, currently I have stopped manufacturing PCBs.
In the free energy group, the first item has zero free energy. light bulb 1 is in series with one leg of the main. Most of the voltage is in series with the diode bridge. Bulb 1 has very little applied voltage. bulb 2 has full voltage applied from the transformer secondary-thus a brighter light.
about induction I want to talk ic irs2453
Please comment under an induction heater article, I will try to help!
Hi Swagatam,
Sorry I should post here, on your
‘Digital Capacitance Meter Circuit Using Arduino’, no comment available. I like to question wether this capacitance meter is only for polar elco or able for non polar elco (run capacitor) as well?Thanks
Hi Awak,
You can check any type of capacitor with that circuit, regardless of whether it is polar or non-polar…..
Thank u 👍
Hello. Good time. I need an ion detector circuit. To find old metals like gold. Do you have such a circuit?
Hi, I do not have a gold detector circuit right now, however I have a deep soil metal detector circuit which can be perhaps customized to detect gold also:
https://www.homemade-circuits.com/deep-soil-metal-detector-circuit-ground/