I am a curious beginner

[krashnburn]

Hi everyone.
I am (obviously) new here

I was looking for a schematic to make an LED fade in - fade out circuit using the 555 timer. Something like this : http://pcbheaven.com/circuitpages/555_Breathing_Pulsing_LED/
I am looking for one that works off a 12v power supply (SMPS of a computer).

Where can I ask this for this help as I am not sure which section would be most appropriate?
Thanks in advance.

[kam]

hello and welcome to our forum!

you can use a 7805 regulator to drop the 12v down to 5 and power the circuit. But a PC supply has a 5V output, why not using this instead??? (red wire-check here: PC Power Connectors)

[krashnburn]

Oh the trouble is I need it to run on a 12v line. The LED strips are designed to work off 12v.
I honestly haven't check if the LEDs work on a 5v line but I feel they may not or if they did, the may not be bright enough?!

[_pike]

You can give 12v to leds and use the 7805 to power the circuit.But i suggest you to see the link that kam gave you because if you are going to use a pc power supply then both voltages are provided.

[kam]

Oh the trouble is I need it to run on a 12v line. The LED strips are designed to work off 12v.

This is going to be a problem then. Search the forum of or the comments of this circuit, because someone else tried to scale the output voltage up to 12V. Maybe he managed to make it work with 12V. Since i've got already many emails/comments for a 12V breathing LED, i may make one more circuit with a more flexible output. This won't happen within this month though since i already have some projects running, and someone has put the magnum on my head for a USB relay driver.

[_pike]

....... and someone has put the magnum on my head for a USB relay driver.

LOOOOOOOOOOOOOOL


Also i would like to ask if he uses a 12v power to the last tranzistor would be a problem?

[kam]

Also i would like to ask if he uses a 12v power to the last tranzistor would be a problem?

No there would be no problem at all, but it would not work. The last transistor is connected as emitter follower, which means that the voltage of the emitter follows the voltage of the base. And since the voltage of the base is calculated to "breath" between 2.8 and 3.3 volts (or something like that), the emitter voltage will remain unchanged. Only the power dissipation of the transistor will be increased and you don't really want that.

[krashnburn]

Hey Kam and Pike. Thank you for your suggestions.
Kam, I wish and hope that the gun to your head is not loaded

I looked through the forum and found this thread: http://pcbheaven.com/forum/index.php/topic,1122.0.html
The strip I plan to use is the same as that guy was talking about.

However I am thrilled at the circuit I mentioned in my opening post as the idea of being able to control the fade in and fade out using pontentiometers is awesome. All I need is to get it to work on 12 v.

*trots off to scour the forum again*

[krashnburn]

Hey guys,

I stumbled upon these circuits:
http://www.bowdenshobbycircuits.info/page5.htm#eyes.gif
http://www.bowdenshobbycircuits.info/page6.htm#eyes2.gif

The first one works off a 9v power supply and the second a 12v. What do you figure out of these? can I use either of them ?
How can I modify the first circuit to run it off the 12v of the PSU?

I hope you have a few minutes for this one in your busy schedule. Thanks a million in advance.
Regards

[kam]

they both use 2 op-amps to generate triangle waveforms (http://pcbheaven.com/circuitpages/Triangle_Wave_Generator), and the second one uses this waveform to generate PWM (http://pcbheaven.com/circuitpages/Voltage_Controlled_PWM_Generator). It is a typical setup. When i was building my breathing LED i originally used this setup because it seems more logical to use it, but i had problems to scale the output to usable levels for the LED. I never test it with 12V though. I declined it because it was far too complicated and i wanted to make something simpler.

[belonmancy]

The triangle wave generator link is not working please provide some other link.

[krashnburn]

I declined it because it was far too complicated and i wanted to make something simpler.

Aaaw. I really wish you had made that simpler circuit that works on 12v
Seems like I have run into a dead end again.

The triangle wave generator link is not working please provide some other link.

It works fine for me now belonmancy
Could you try again?!?

[kam]

Aaaw. I really wish you had made that simpler circuit that works on 12v

wish i had more time to make 100 circuits in a day. but i spend many hours for each circuit, because i do not copy, instead i design them from a scratch. This requires more time than usual, and also i run many tests before i publihs. I will make one 12V breathing LED for sure, because i've been asked by many people. I just do not know when. Hopefully before the end of this year.

[krashnburn]

Ok I am back
So here is the thing. While the circuit I found would have been simpler to construct, turns out that not all the components are that easily available. Here is where I hit the road block - I cant find 100 uF capacitors that are non polarized. Talk about sh*tty luck

So the search continues. I was busy with modding a cabinet and hence this had slipped my attention but now I am back on it.

@Kam - Hey howz it going!? Wish you a Merry Xmas and a Happy New Year. Hope this year brings you more time for all the things that you love to do

[kam]

Hey mate, thanks for the wishes. Wish you also merry xmas and a happy new year. I was on short vacations and i returned yesterday.

Which circuit requires a non-polarized 100uF capacitor??? You can connect capacitors in series to increase their capacitance, but send me the url to have a look. it is kinda strange.