LEDs synced to music question(s).

[goalio35]

Basically my project is this; I'm building a DIY subwoofer for in my room, and I would like to have yellow LEDs wired underneath the enclosure, that pulse with the music. Like the example found **broken link removed**

First of all, if someone could look at my schematic and see if it will work, that would be very much appreciated. I'll list my references for my design bellow.
**broken link removed**

LED Specs:
Useable Voltage is 2V
Power Dissipation =20mA 48 mW
Forward Current = 25 mA
Forward Voltage =20mA — 2.0 V (typ.) 2.4 V (max)
Reverse Voltage =10μA 5 V

Resistors:
180 Ohm 1/8 Watt 5% Carbon Film Resistors

Power Supply:
12Vdc regulated output
1.25 Amps
15 Watt
Universal AC Input 90-264Vac
No minimum load requirement

I used the following to come up with my schematic design:
This schematic **broken link removed** (From the link above)
AND
View attachment 61829 (From ledcal.com )


My only other questions would be:
1) Where to connect the the line for the audio?
2) Where to ground it?

This is the **broken link removed** I am using to power the sub, if that helps in answering my hopefully simple questions. Hopefully I remembered everything needed to assess my situation.

I just realized if I change the value for "voltage drop across LED", from 2.2 to 2.0 in the ledcalc, I'll need a 220 ohm resistor instead of 180 for my LEDs. The specs for the LEDs say 2.0 typ and 2.4 V max... Does that mean it could still work? Or are these two different things? (voltage drop and forward voltage that is)

Thanks, Tim

 

[Sceadwian]

It doesn't really say how they connected it, though it going to a stereo jack implies that you would connect it to a line out signal that's the same as what's going to the sub, doubt you can use a Y connector as the transistor will cause distortion so it'd have to be from a buffered audio spliter. You would need to adjust the volume control on the tip31 independently anyways to get the results expected.

If the VF is higher the LED's will simply be slightly dimmer, if you really care test them, I wouldn't bother just use the typical value and be done with it.

You would ground it to... well... ground =) There's a solid chance your power supply is already grounded, just double check.

Voltage forward is a term for diodes only in general, voltage drop is a generic term for the difference in voltage between two point, usually associated with a resistance, though diodes have a voltage drop as well it's not linear like a resistors.

 

[Sceadwian]

Just an additional note, there is no isolation circuitry in this simple schematic, so it HAS to be connected to an isolated output (like a lineout signal which is capacitor isolated) if you connect this directly to a DC source without some way to limit current into the TIP31's gate it easily burn out if the source can provide enough current.

 

[goalio35]

Not sure if MY schematic link worked or not (its not for me) so here it is again just in case...
https://i927.photobucket.com/albums/ad119/paptim22/schematiccopy.jpg

That makes sense though, and thank you for your reply. I guess my question really was, if I can just splice a wire from the input to the woofer amp, to the TIP31 for audio in. The subwoofer amp actually has "high level out" and its supposedly just the same exact thing as the signal going into the "high level in"... I don't plan on plugging in any speakers to the out, so I'm guessing I could just run some speaker wire from there, to the TIP31? Would this mean I have to amplify the signal to the tip31 to get the expected results? I read something about that in the comments on the site where I got the original schematic...

"Thanks for the help. Still don’t know what was wrong but it is working now. I think it may have been I didn’t have the volume high enough. Is there a way that I can make the LEDs flash work at a lower volume level so I don’t blow out my ears?"

Response: "Use an lm386 chip to amplify the audio signal going to the LEDs"

As for ground, I actually thought of that after I posted this so that should work!

If I understand what you're saying, I need a resistor between the power supply and the TIP31? The specs for the TIP31 are "100V 3 Amp", and the power supply's output is 1.25 Amps. Am I in the clear?

 

[audioguru]

The circuit is An Instructable that was designed by a 10 years old kid who knows NOTHING about electronics:
1) There is no current limiting for the LEDs so they instantly burn out.
I am glad to see that you are using current-limiting resistors for the strings of LEDs. But your calculation is for 20mA DC. 20mA AC (sound is AC) needs half the value of the resistor because the LEDs are turned on for only half the total time.
2) There is no current limiting resistor for the base of the transistor so it or the amplifier will instantly burn out.
Your 70W into 4 ohms amp has an output swing of 24V peak. For a max base current of 7mA then the series base resistor should be (20V - 0.7V)/7mA= 2.7k ohms but 1k is fine.
3) The reverse voltage into the base of the transistor will destroy it or your amplifier since its max allowed reverse base-emitter voltage is only 5V but your amplifier gives it 24V. Add a diode in series with the emitter to ground.

 

[goalio35]

Hey thanks for you reply Auidoguru. I did get it working... one row of 4 at least. I just used the original plan. Heres a video in case anyone cares to see.

 

[audioguru]

1) What prevents the base-emitter diode of the transistor from burning out or prevents the stereo amplifier from burning out since a series input resistor is missing?
2) What prevents the transistor reverse-biased emitter-base diode from having avalanche breakdown which will destroy it and will destroy the stereo amplifier because a diode is missing?
3) What prevents the LEDs from burning out since a series resistor is missing?