Need help with simple audio to flashing LED project

[silverslik1]

Hey

I'm trying to build these projects: Music LED Light Box or Blinking leds (they are really the same project) that take audio and make an LED or a series of LED's blink with the beat or rhythm. I can get it to work, except the LED's are very low and are very dim and do not blink with the intensity in the video. I am using two 9 V batteries in series at around 17V and the LED's are fine because if I connect them to a source and a resistor, they get around 20-30mA of current which is ideal. In the setup I have now where they are very dim, they get only around 1-4mA MAX which is the problem for obvious reasons.

Anyone know a reason which could be giving me such a low amount of current? I've tried changing the voltage, but when I had 9V's in there, it did not make much of a difference and when I have 17V in there, it is still at the same intensity.

Thanks

 

[Dragon Tamer]

We've actually seen this before on this forum, the problem that was not mentioned in the schematic is that neither the LEDs or the transistor have any current limitation. You need to add a resistor to the base of the transistor as well as the the common of the LEDs. You also don't need to have a darlington aray in the design, a simple transistor will work just fine.

I made something simple like this for one of my projects except that the audio input went into the control pin of a 555 timer.

 

[silverslik1]

I have used a resistor, right now, it has a 280 Ohm resistor (a 100 and 180 in series) from the source of the transistor to the start of the LED's that are in series and it does not help only hurts. When the resistor is in series, it makes the current go under 2mA. Do you have a schematic of the project you made?

I've been looking at videos and drawings all day and I can't seem to figure out why mine is the only one doing it. I've tried rebuilding 4 times with 2 different guides and a youtube video- I consider myself to be an avid circuit builder as well!

 

[MikeMl]

The circuit on Instructables was created by somebody who knows nothing about LEDs or transistors. Most of the stuff I have looked over there is pure crap. As mentioned above, there needs to be some current limiting both in the transistor's base, and in series with the LEDs themselves.

The lack of current limiting in the base can (depending on the voltage level of the input signal) create severe distortion in the audio by asymmetric loading of the signal on positive peaks.

Here is what I would do to fix it. I am assuming that the LINEOUT from the sound card is under 2Vp-p. To make the circuit more sensitive, I biased the transistor to where it is just on the verge of turning on, and then capacitively coupled the audio to the base. To limit the current both through the base and the LEDs, I put the resistor in the emitter of the transistor. The simulation shows the current through the LEDs for a burst of audio... The peak current of 11mA should make the LEDs bright...

 

[silverslik1]

Ok, could you describe that circuit a bit more? I see the 4 LED"s in series, is the positive terminal hooked up to V2 or does V2 go into the negative (anode) to the LED's.

Is there resistors and capacitors before from the audio line? I'm just very confused on how to go about connecting this- and reading that diagram.

 

[MikeMl]

Instead of doing this for you, I will lead you to water, and see if you can drink.

TIP31C btw: almost any small-signal NPN transistor will work.

Blue LED Other colors will work, too. DigiKey has thousands of types of LEDs.

Capacitor Value not too critical, especially voltage rating.

Circuit board

 

[silverslik1]

Oh I have all the parts!! I'm just having trouble understanding what goes where and how they all plug into each other....it just seems confusing from the schematic

 

[MikeMl]

Click on the links for the data sheets for the parts I listed. Each one has a pinout and physical picture of how to connect it. There is a one-to-one correspondence between the "nodes" in the schematic diagram, and the connections to the physical parts. That is why schematic diagrams (and pinouts of the physical parts) convey sufficient information to build any electronic circuit.

If you would like me to check your work, draw a picture of the physical parts with interconnections, and I will check it for you

 

[silverslik1]

I think it was my LED's because a friend had another one from Radio Shack and it seemed to be much brighter, could this be the case or am I just imagining it? ALL LED's that are 5mm are not created equal? I think they both are that size atleast- they are red as well.

 

[scarygood536]

I think it was my LED's because a friend had another one from Radio Shack and it seemed to be much brighter, could this be the case or am I just imagining it? ALL LED's that are 5mm are not created equal? I think they both are that size at-least- they are red as well.

5mm has nothing to do with it. it's the MCD intensity and color. read the back of the RS led package and you will see it list this information. Your friend might have bought a brighter LED. Quite possible if you made the second circuit you could have partially burnt out the LEDs. There are plenty of other schematics floating around this sight to achieve your task, but MikeMI has provided a relatively simple circuit. If you build the second schematic i'd be careful on the volume you put your music source at. Also I wouldn't use it long as you can burn up your audio card.