The following article explains a simple circuit which can be used for alternately switching LEDs with gradual brightening and fading effects.
Simulation and Working
The circuit can be effectively used for generating spooky effects in idols, for example it can be used for illuminating the eyes of a Jack-o'-lantern during haloween celebrations.
The circuit is overly simple and requires just a couple of opamps and a few other passive components for implementing the proposed brightening and fading actions in the LEDs.
The opamps can be a couple of separate IC 741 or a single IC with dual opamp such as IC 1458, 4558 or a TL072.
The opamp A1 is used for generating a gradual rising and sinking voltage, which ranges from 3 to 6 volts.
The opamp A2 is simply configured as a comparator for supplying an alternately varying voltage between 2 and 7 volts in order to charge and discharge C1 and C2 through a constant current input.
Thus the above operations become responsible for generating a linear peak to peak ramping signal at pin#1 of A1.
This signal is amplified with a couple of transistors wired as emitter followers to pin#2 of A1. Here the LEDs become the emitter loads of the transistors.
R4, together with C1 and C2 determines the rise and fall frequency of the connected LEDs.
R4 can be replaced with a 100K pot for making the fading rate manually adjustable.
The circuit should be operated from a 12V DC power supply for supporting at two LEDs on each channel.
For accommodating more LeDs, the collector of T1 and the upper end of R7 should be connected to a separate high voltage supply may be to a 30V supply which would then allow the connection of 6 LEDs on each channel.
Parts List for alternate brightening and fading LED circuit
R1, R2, R3 = 56K,
R4, R5 = 120K,
R6, R7 = 150 OHMS
C1, C2 = 33uF/25V
T1 = BC547,
T2 = BC557
LEDS = 5mm, 20mA,
Abhinandan Sharma says
i am using an led light strip.. the circuit is correctly connected but the fading effect is not shown.. what should i do now?
Swagatam says
did you connect the 741 pinouts correctly? use a single LED or 2 LEDs as shown in the diagram to test the effect, don't use strip.
Abhinandan Sharma says
yes i have used all connections correctly also i have tested the circuit for single led but the result is the same… should i connect the +ve terminal of power supply to pin #7 and negative to pin #4?
Swagatam says
how can you say you did everything correctly when you have not connected the pin4/7 to the supply rails?
obviously you must connect them to the supply, otherwise how will the IC work…?
Abhinandan Sharma says
have i used the correct opamps?? there is no #9 and #11 pin on opamp A1
Swagatam says
for IC 741, pin#7 is the positive supply, and pin#4 is the negative supply pins.
pin#3 is the (+) input pin
Pin#2 is the (-) input pin,
pin#6 is the output.
you must modify the connections according to this
Abhinandan Sharma says
but in the circuit given there is no connection of power directly to the IC through pin #t and #4
Swagatam says
the diagram shows a dual opamp IC, that means two opams in one package.
Abhinandan Sharma says
What is A1 and A2?? I made the whole circuit,connected everything but it's not working.. i used IC 741 as A1 and A2
Swagatam says
A1 and A2 are opamps, please check all the connections once again and also the polarity of the capacitors…you can also try reducing the voltage to test the response
kikira says
Good morning sir,
THANK YOU VERY MUCH…. 🙂 🙂 🙂
K.Kausik
kikira says
Sir,
I'm really sorry. Apologizing for any kind of mistake.
I didn't maintain the name with any kind of intention.
Actually I always try to gather information before asking you anything,just to provide you more free time,that you may help others, all over the world. Not only me but the visitors out of India also appreciate your attitude to help and responsibility to answer as soon as possible. And that adds some extra colour in your website and it's the only green tree in the desert.
I really feel proud to you and like to pray for your prosperity and happiness.
Again I'm really sorry for any kind of mistake.
Thanking you,
K.Kausik
Swagatam says
Kaushik, please do not apologize, I know that you innocently included the external link without knowing that such links were not acceptable in most websites….
You are one of the avid and dedicated readers of this blog and I appreciate and value your involvement very much.
So please keep up the good work and feel free to comment whenever you have a query or doubt regarding anything in electronics.
kikira says
Sir,
Sorry for reposting …..
Thanks for kind and quick response….
k.Kausik
Swagatam says
No problems kuashik…keep up the good work
kikira says
Good morning sir,
There were a request,that I posted here yesterday but somehow it didn't appear here ! ! ! !….
Actually I want to control a 5Mts led strip(China made,with its own power supply;12v, .75amp ).
Is it possible with 555ic and/or what will be the transistor value.
I have done with another page that explains different types of fader circuit with 555ic. And there are 139 no of comments and I'm not so wise to find out the definite solution. So I'm here to disturb you. Any suggestion….
Thanking you,
K. Kausik
Swagatam says
Good Morning kaushik,
comments once posted will 100% reach me, it might get slightly delayed but all will be answered appropriately.
If you want to use a 555 circuit, you can build any standard IC 555 astable circuit and use the transistor stage which is explained in the above article along with C1/C2 with its pin#3 for the same results.
Simply by connecting the C1/C2 end with pin#3 of the IC 555 astabe you should be able to get the identical fading effect from a 555 circuit also.
Swagatam says
Kaushik, I did not publish your last comment since you had an added an external electronic site's link in it (sorry that's not acceptable here)
I 'll surely try to answer your queries in my free time…
kikira says
Sir,
I want to control a 5mts(China made) led strip available in the market with its own power supply(12v,.75amp). Then which ckt is most useful;this one or any 555 one,explained in another post(actually there are 139 comments and I'm not so wise 🙁 !!! ). Please inform with desired transistor values.
Thanking you,
K. Kausik
Anil Kumar. K says
Hi Swagatham,
Sorry, I forget to tell you this important things.
My IC is LM358, LED…..1 blue led with series resistance 330ohms. Its ok now with c945 transistor. But I would like to control many leds using N mosfet.
Swagatam says
Hi Anil, If the circuit is working well with BJTs as recommended in the design then I think it's better to use BJTs only instead of mosfets which are not giving proper results.
you can try 2N2222/2N2907 or 8050/8550 in place of BC547/BC557 and use many number of LEDs in series/parallel combinations as per your requirement.
also you can try replacing R2, and R4 with 100K and 1M pots for getting an adjustable feature from the design
Anil Kumar. K says
Hi Swagatham
Thanks in advance.
I assembled this circuit. R1 & R2 47k and R4 150k, T1 2sc945. Supply 12VDC. Circuit did not worked. LED always ON.
I reduced supply voltage to 9v, R2 to 33k. Then the fading effect started. But rising and falling were not perfect. I replaced R4 with 1megaohms. Now rising-falling timing ok as I desired.
I replaced c945 with N-mosfet 50n06. Again I lost fading effect. LED always ON. I changed supply 9v to12v. But no benifit.
I have many 50n06 N channel mosfets stock. I want to control 2 channel LEDs, 1 fade ON then the 2nd fade OFF with 2 N-Mosfets. Supply must be 12v.
dhivya krishnan says
Hiii this project is very useful sir.. I have a doubt how to connect audio jack with a mobile phone …
Swagatam says
Hi, thanks, why do you want to connect it with a cell phone audio?
this is not a music level indicator circuit……
Thilanka Thilina says
hi swagatam,
first of all i love what u do here… cuz not like most of the blogs u explain how it happens in a simple understandable way. even for a newbie like my self, its easy to follow up. keep up the work. i love what u do.
now my question.
1)i am planning on setting this up in a vehicle (12V 95A) in 1w LED's.
is it possible to do it with this diagram? i would like to put
around 4 LED's.
2)And to the home electricity and again same 1w. here i want to put around
10 LED's.
Thilanka Thilina says
Hey swagatam,
any help on this ? plz ….
Thanks ..
Swagatam says
Hi Thilanka,
Yes you may do it using the above circuit, there would be some mods needed, though:
Replace T1 with TIP122 and T2 with TIP127, R6 and R7 should be replaced with 10 Ohm/2 watt resistors.
Rest all remain as it is.
Regards.
Swagatam says
You may first try using 8050 in place of T1, and 8550 for T2…..if it doesn't work then you may go for the above transistors.
Thilanka Thilina says
thanks swagatam, will try and let u knw the results.. keep up !!
Jineesh M says
Hi Swagatam,
How connect this circuit for control Two 40W/230V Bulb (using TRIAC)
Swagatam says
Hi Jineesh,
It will be a quite complex circuit to build.
Anonymous says
It's not complicated, just put 2 optocuplers with triac on output (MOC series, it's MOC30something, you can find it on internet) and those optocupler to drive big triac with enough power for bulbs. 🙂
Swagatam says
what about the fading effect??
Bibin Edmond says
hi swagatam,
yaar i have a doubt on led current… What is the total current of a led string connected in series.
No of leds : 10
Led voltage drop : 3V
Current of each Led : 20ma
so what will be the total current of this string ?
is it 20ma or 200ma.. ?
and which is suitable powersupply for this string.. ?
1. 30v 50ma
2. 30v 200ma
Swagatam says
Hi Bibin,
It will be 20 mA.
The suitable PS would be 30V/200mA, because 50mA would be insufficient and cause the voltage to drop below 30V.
Bibin Edmond says
That's the one thing i can't understand yaar.. ! The total current for the string is 20mA right, Then why we need that 200mA powersupply…?
Please help me yaar.. can u explain why we need that 200mA current.. ?
And how did u calculate the current needed for the same string… ?
Swagatam says
The current rating of any power supply shows its maximum capacity of delivering current. If drawn at this level the voltage will tend to become zero.
For example our home AC is rated at around 40 amps, upto 3 or 4 amps, the voltage doesn't drop, but above 5 amp load the voltage begins dropping. At 20 amps the voltage might drop to 150V and so on..
Therefore the PS current should be sufficiently above the required load current.
In series connection the current will be the same for the whole LED string
Bibin Edmond says
oh… ! thanks yaar… !
Anonymous says
Suitable power supply must be at least 20% more than summa of LED voltages for eficient work. That means 36 volts, but stabilised. than you calculate resistor to put to reduce this 6 volts. 6 volts and 0.02 amps, thats 300 ohms and 0.12 watts. It's better to make parallel- series conection with 2 diodes and resistor in series and 5 of those in paralel. 🙂
Anonymous says
Hi
i m wondering how this circuir works – http://mdpub.com/555Controller/
can u plz explane how the low battery and full battery auto cut off works with the relay and whats the differencr between dumping and dummy load means r they the same
i made one of this and cannot calibrate
does the relay energiza and until the battery runs low and then deenergizas ?
kind of mess no clue
plzzzzzzzzz help
Thanks !!
Regards…
sam
Swagatam says
It's nothing but a comparator circuit having low and high cut off setting facility.
"Dump" switch is for manually forcing the IC into cut off mode and "charge" is to manually bring the IC to charge mode, irrespective of the battery charge conditions.
Calibrating it will require some expertise in the field….