# UV LED Color Organ

Discussion in 'LEDs and Optoelectronics' started by muk, Jan 9, 2010.

1. ### muk

3
0
Jan 9, 2010
Hello, this is my first post to this forum and I'm pretty much a noob to circuit design as well, I hope you'll bear with me.

I've made a functioning single LED, single channel color organ but am unsure about the design. I'm thinking that the LED may be getting too much current and I don't want it to prematurely burn out.

My goals for this project are:
1. To be able to amplify the audio voltage so I don't have to turn the volume all the way up and have the possibility of using a line-out level audio signal.
2. Eventually split the signal into high/mid/low frequencies to activate 3 LEDs
3. Convert the design to use USB 5V

Thanks for any help!

the schematic shows 2 LEDs but it works with one as well (with possibly too much current)

File size:
26.1 KB
Views:
1,960
2. ### muk

3
0
Jan 9, 2010
OK, I learned a bit more about resistance and LEDs .

I've changed the design to just one UV LED with 2 220 Ohm resistors in parallel which gives a total resistance of (220*220)÷(220+220) = 110 Ohms

Which is perfect for one 3.2V 20mA LED, (5.45V−3.2V)÷(.020A) = 112.5 Ohms

So now I'm wondering how I can fully power more than one LED on this circuit, is it possible?

Revision 2 of schematic attached.

File size:
26.3 KB
Views:
4,876
3. ### Resqueline

2,848
2
Jul 31, 2009
Those schematics are entirely wrong, I don't see it doing anything but blow the LED &/or the transistor. And where's the audio input?
The LED is supposed to be in series with the collector resistor, and you'll need to bias the base a little & use a capacitor to insert the audio signal.
Google "common emitter amplifier" for correct circuit diagrams and design examples.

4. ### muk

3
0
Jan 9, 2010
Thanks for the information!

The audio input is on the lower area. It produces from about 0.02 to 0.08 Volts when there is music playing.

It seems to be working half decent now, the LED has been pulsing with music for over an hour now and none of the components are hot.

I'm looking into the common emitter amplifier now. I imagine that I'll need it to be inline with the positive and ground of the audio signal before it hits the transistor so that the voltage is boosted, is this correct?

First though I think I'm going to try making a Darlington Pair with two transistors as it seems to achieve a similar end.

Augg, I need a breadboard... all these alligator clip wires are making me nuts.

So I think I've made something along the lines of this -> http://www.allaboutcircuits.com/vol_3/chpt_4/5.html

I don't want to have to add another powersource inline with the base just to bias the waveform which seems to be triggering the transistor in a suitable fashion already, I just want to have the transistor be more sensitive somehow. I think by making the darlington pair I lose too much voltage for it to be effective and it doesn't seem to work any better at low volumes anyway.

Last edited: Jan 10, 2010
5. ### Resqueline

2,848
2
Jul 31, 2009
Ok, you must have connected it different from the schematics then.
Remember that the transistor won't even begin to conduct until it reaches a base voltage of 0.5-0.6V so it's only the very highest peaks of the music that is now able to turn on the transistor (& LED).
Making a darlington connection will only make matters worse with its 1-1.2V base requirement.
You don't need another powersource. The bias is always accomplished with two resistors in a voltage divider fashion.
You want to put the base at 0.5V or so (where it just doesn't conduct). This'll make more of the music waveform put the transistor into conduction and therefore increase the sensitivity. A 10k from positive-to-base and a 1k from base-to-ground should do the trick. Then a 1uF (or so) capacitor to fed the music through.
Darlingtons are used when you need the current to be amplified a lot, but that isn't the challenge here - as the audio output has plenty of current available to drive the transistor, but not enough voltage.
Hehe, yes, a breadboard would certainly make life easier for you..