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# Increasing voltage

#### kevinmd88

Mar 14, 2013
2
A little background first:

All I'm trying to do is attach some 12v LED strips to the speakers in my car such that they will flash to the music. I attached a drawing of the circuit I did in Paint that should describe what I'm doing, but essentially, the +/- of the speaker wiring (post-amp) is directly connected to the +/- of the LED strips, and a toggleswitch is added, as well as a low-pass crossover so only low frequencies (bass) will be detected by the lights, which are in series.

I did a test run on one LED strip to make sure everything is okay, and it actually does work. The only problem is I have to turn the volume way up on the stereo to get them to light up. I used a multimeter to troubleshoot and found out the voltage directly before the LEDs is too low. (As mentioned before, the LED strips are rated at 12v.)

So, to finally get to my question for you guys: Is it possible to "boost" the voltage so the lights will flash at reasonable volumes?

Thanks in advance for any advice you guys can offer

#### Attachments

• series circuit2.jpg
15.8 KB · Views: 70

#### Electrobrains

Jan 2, 2012
259
According to your circuit diagram you have put all 4 strips in series. That would demand 48V for full power!

Try to put only 2 in series plus a suitable resistor.
If that still would demand higher voltage, then use them single with a resistor.

You could also use that resistor as part of a low-pass RC filter, if you put a capacitor directly parallel to the LEDs

Of course you can amplify the output voltage and add AGC (Automatic Gain Control) functionality etc, but that would be complicated.

#### kevinmd88

Mar 14, 2013
2
Thanks for the quick response Electrobrains

You're absolutely right! I think I've confused the properties of parallel vs. series... In order for the LEDs to receive 12v each they'd need to be wired in parallel. Thank you for pointing that out I'm somewhat new to all this stuff.

So I'll change that, but the problem remains that the voltage coming from the speakers, even after the amplifier, is too low to make them light up... I feel the only problem is I need to supply the LEDs with more voltage... Or, somehow, lower the voltage they need (which I don't think is possible).

But I'm trying to figure out how to do that without causing the LEDs to be on all the time. For example, if I were to somehow use a power supply to supplement the voltage coming from the speakers - e.g. 10v stable + whatever is coming from the speakers - I'd think they would be on all the time because the *minimum* they'd receive is 10v. (Those numbers are just demonstrative examples)

PS: The LED strips I ordered (linked in the original post) have resistors built in.

#### duke37

Jan 9, 2011
5,364
You will need a circuit to detect the speaker signal, this would then be used to switch the leds using a fet.

#### Electrobrains

Jan 2, 2012
259
You will need a circuit to detect the speaker signal, this would then be used to switch the leds using a fet.
Here is an example of a very simple circuit that can drive LEDs or LED strips from audio signals (price <1\$).
Adjust the level with P1.

I suppose in this case only three or four components would be needed.
Suggested:
T1: TIP112 (supply voltage could be up to 100V)
R1: 10k
P1: 10k
(R2: 56k)

Some other functions could also be made with this circuit (low-pass and high-pass filtering, peak detector/indicator etc.)

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