In the following post I have explained a simple circuit which can be used for alternately switching LEDs with gradual brightening and fading effects.
Circuit Operation
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 op amps 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,
Comments
Sir,
Sorry for reposting …..
Thanks for kind and quick response….
k.Kausik
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
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.
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
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.
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
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.
Hiii this project is very useful sir.. I have a doubt how to connect audio jack with a mobile phone …
Hi, thanks, why do you want to connect it with a cell phone audio?
this is not a music level indicator circuit……