Speakers with sound reactive leds

[COREGAMER]

I want to add some sound reactive leds to my speakers (2.1)
however I have a problem
When I try to get multimeter readings for the voltage it doesn't show the voltage.
I tried to get readings from the psp speakers and they too didn't show any voltage.
But when I connect an LED to the 3.5mm jack it lights up

Is there a special multimeter setting to get readings from speakers?I tried both AC and DC

[Crumbz]

i dunno about the multimeter setting... it should work on Volts.

and are the speakers USB powered?

[COREGAMER]

nope the subwoofer is powered by the mains and then the speakers are connected to the subwoofer through RCA

The voltage on the speakers isn't much as when I connect an led to it it doesn't burn out.
I suspect it might be around 3 volts but it would be better If I could get a reading.
I also can't find good multimeters and chips like the LM386 where I live (India).
Electronics is a little hard for me, they'll teach us basics in school in 2 years time, I'll post an update when I understand.

-Jaideep

[FOOKz™]

good question
You cant really measure voltage of a sound wave because the amplitude "volume" or voltage of the signal changes all the time in a non-linear fashion.

There is a way but you need special equipment.


BUT! I know you are going to ask well AC's voltage changes, how come you can measure it?
AC's voltage changes in a predictable pattern that we know how to measure.

[zack247]

so then what if you played a continuous sound from the speaker with a wavelength similar to AC voltage?

i know nothing electrical about sound BTW.

[FOOKz™]

Yep. Check the attached MP3 file. It is a 1KHz tone (thats annoying as crap!). Play that and try to measure AC voltage with your meter. If you dont read anything turn the volume up all the way and see if you get anything.


The way you are going to do it is very crude and you won't get any accurate reading with your meter at all because most meters are calibrated to measure 60Hz NOT 1KHz. (1KHz = 1000Hz) The reason for this is 60Hz is the AC frequency that comes from your wall outlet!!!

The best way to be sure to get an accurate voltage reading is with a piece of equipment called an oscilloscope. If you have an electronics repair shop around town they might let you use it if you ask.

[COREGAMER]

ok so nevermind that
I connected 2 blue Leds in parallel to the speakers with a 10 ohm resistor.
Now the problem is that the leds only light up when the volume is high.Is there a way to make them light up on low volume too.
I want it to be like the PSPs led mod where the leds stay on as long as the speakers are on.


The speaker module inside says 6W, 4ohm.



Edit-I can't get a reading from the 1kh file

[FOOKz™]

Use an LM386 to amplify the sound going into the LEDs with this
https://www.acidmods.com/forum/index.php/topic,28600.msg208015.html#msg208015

Parts can be found at radioshack.

[frenulem - No.5417]

Honestly it's not good practice but take out the resistor,  I never had any issues when not using a resistor, unless I have magic LEDs

[COREGAMER]

I don't think I should do that because the leds burned out when I did it without the resistor

[COREGAMER]

Here is a video of the mod

I know its not that good but it is what it is


http://www.youtube.com/watch?v=9Runu7vmHNs

[Crumbz]

yeah that looks normal to me.

but if you wanted to have them stay on while the power is on you would have to open up the sub and find the amplifier in there and hook a power flow up to the leds and they will react as well as stay on. But the power to the sub is alot so a multimeter and resistors are recommended

[Kool1zero]

If you like the kind of flash effect but want more of a fade out affect then toss in a capacitor in parallel across the speaker outs.

what voltage are your LEDs? i can calculate some suggested values for resistors and such

[FOOKz™]

looking good coregamer !! Thats almost perfectly adjusted lol. Just like koolone0 said you can put a cap across the speaker outputs (going to the sound reactive circuit) to let it fade) The capacitor charges and discharges every pulse, the discharging is seen by the LEDs are fading out slower.

[COREGAMER]

thanks guys

@koolone0 - The Leds are rated 3.4volts,20ma and I have 2 of them connected in parallel with a 10ohm resistor.

And what kind of a cap would I need? how many uF and such

[Kool1zero]

I'll have to pull out my Circuitry book from class last semester.
but basically, the bigger the cap (more F) the slower the fade out

Edit: any type cap should work, that being said: if you use and electrolytic make sure its in the same polarity as the LED

[Kool1zero]

Honestly it's not good practice but take out the resistor,  I never had any issues when not using a resistor, unless I have magic LEDs

you may have been buying resistors with built in resistors

[FOOKz™]

Pulsing current has a less chance to burn out LEDs if they dont have resistors too