Hi Friends, I am Swagatam. Most readers know me through homemade-circuits.com, a website I started in 2011 to share practical electronics knowledge with hobbyists, students, and working engineers.
Some people also know me by the name Swag, Swagat, Sagar…
I completed my electronics studies at DIPIETE in 1994 and since then I have spent decades working hands-on with electronic circuits, learning how they actually behave beyond textbooks, you only learn that by doing.
About homemade-circuits.com
I started homemade-circuits.com with a simple goal, to make electronics concepts easy to understand and genuinely useful for people who want to learn and build circuits themselves.
Before this site, I worked as an electronic circuit content writer at Brighthub. Then in the year 2013, I started the site homemade-circuits.com.
How This Site Is Different
On homemade-circuits, I personally read and reply to comments. Over the years, I have answered more than 50,000 circuit-related questions, helping readers troubleshoot problems and improve circuit designs, step by step.
Many circuits published here get refined through these discussions, becoming more reliable and practical over time.
A Bit More About Me
Outside electronics, I am an animal lover. I have rescued dogs, cats, and birds, and one long-term goal is to build a shelter for injured and abandoned animals, still working towards that.
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If you need help with any circuit on this website, post your question under the relevant article. I always try my best to provide clear and practical guidance based on experience.
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Comments
Hi,
In my micro-controller based system, I want to add a battery with charging circuit to power the system as on-line UPS. I have studied your different battery charging circuits and want to use LM317 based battery charging circuit designed by Mr. V.
(https://www.homemade-circuits.com/wp-content/uploads/2022/12/LM317-battery-charger-circuit-with-13.75-V-output-fixed.jpg )
I want to detect the presence / absence of battery and the battery charging current.
My question is, How should I detect that battery is not present and if battery is connected what is the charging current ?
Hi, The best approach would be to put an analog ammeter in series with the positive line that goes to the battery positive…nothing else is required…the meter will show you the presence/absence and the exact current being drawn by the battery….
https://www.homemade-circuits.com/wp-content/uploads/2025/11/2-amp-ammeter.jpg
Instead of analog ammeter, I want to use my microcontroller to read the charging current & battery presence. The microcontroller have 10 bit internal ADC.
If I read the voltage across Shunt resistor, the ground supplied to my microcontroller & negative terminal of battery will be at different potential. Am I correct ?
So what will be the best way to achieve this ?
Yes, you are correct…in that case you can employ an opamp based design as explained in the following article, and then integrate its output with your microcontroller…
https://www.homemade-circuits.com/how-to-sense-current-using-op-amp-low-side-and-high-side-circuits-explained/
Hello Swagatam 🙂
Please help me find a scematic how to build an Sequential Turn Signal Light for Cars – 12V ordinary lamps!
Like the running light on an old Ford Thunderbird -66 car or like an Mercury Cougar turn light.
Is it possible to build this circuit with Mosfet IRF 511 for lampbulbs. Not LED lamps.
I will be very grateful if you can guide me.
Greetings from Kurt in Sweden
Thanks Andersson,
I can surely help you, please let me know if you want the LEDs to illuminate one at a time while chasing, or illuminate the whole bar one by one and then once the whole bar is lit, shut the whole array and start again??
sir, I need a over load cut off relay which will cut off say above 500watts at 230v ac . However when the over load is removed or the power falls below 500watts it should connect automatically. This is to avoid excess usage of power by several rooms simultaneously which will damage the wiring at the same time and also to avoid manual intervention required like fuse, mcb and other conventional over load circuits.
Sir i thank you for your quick responce. I think if relay latch is removed it may start chattering. once live line is disconnected led of opto coupler will not glow which may de energize tht relay and connecting the live line again. However I will try to mody the circuit to over come this problem. Thanks for the idea.
You are correct Ravindran, without latching, the relay would chatter at the cut-off ranges, so latching is a must. Or you can consider adding a delay network across base/emitter of the BC557 transistor…
Ravi, you can try the concept explained in the following article:
https://www.homemade-circuits.com/mains-ac-overload-protection-circuit/
Since you do not want the circuit to latch, you can remove the R6 resistor link from the circuit.
Also, the opto coupler can be any 4 pin standard opto coupler, it does not need to be an LED/LDR type opto.
Therefore the push button can be also removed, and P1 can be replaced with a 10k resistor.
Just make sure to connect a 1k series resistor with the collector of the opto coupler transistor, so that the base of the NPN BC547 transistor remains safe from any over current situation…
I’ll get right to the point: is there a simple way to have LED’s not go ON/OFF but rather with a very short ramp-up and ramp-down, like incandescent light bulbs do? And this in the simplest/smallest way possible. So I assume with capacitors rather than with PWM. I would like to incorporate LED’s as direction indicators in model cars. Any suggestions would be highly appreciated. I already read a lot on the subject here but am looking for more directions and tips. Thank you in advance, Dirk
That looks possible, to provide a slow fading and rising effect to the LED using a transistor driver. So for this we can use an NPN transistor driving the LED at its collector, with its base getting the ON/OFF switching voltage through a resistor, and a capacitor connected between its base and ground executes the soft ON/OFF on the LED.
Let me know if you find this OK…
My god, you are fast! 👏🏼 I think I could use this information but as a novice I would probably struggle with finding the right values for the components. Maybe not for resistors but more for the capacitors and transistors, power supply etc. I’m literally the opposite of you regarding knowledge on electronics 😞
No problems…you can try the following set up for the proposed aapplication:
https://www.homemade-circuits.com/wp-content/uploads/2025/10/slow-fade-LED.jpg
The LED resistor, ad transistor base resistor can be adjusted as per the LED current, same for the transistor, and 220uF can be changed to adjust the fading effect delay…
Thank you very, very much for your time and knowledge.
Hi, can you advise on a design for a solar powered dual power supply for op-amps, for example +-12v ?
Thanks, that was super quick !
Hi, you can try this:
https://www.homemade-circuits.com/wp-content/uploads/2021/03/precision-dual-power-supply-using-IC-741.jpg
I have a heating element out of an old dishwasher that I would like to heat rainwater with and to keep it at a constant 40 to 45 degree to prevent freezing. Is this possible and do you have a circuit I could build on hand. Thank you from a retired newbi.
Can you please post this question under a relevant “temperature controller” article, i will try to solve it for you…
Ok I will try that one for you.