Author Options:

How can I make my car light show light up at lower volumes? Answered

Please help me out if you have some basic knowledge of electronics! I am trying to make an array of LEDs pulse to the music of my car stereo. I am basically just running the car's battery power and the preamps on the back of the stereo out to some transistors. The only problem is that you have to turn the stereo up really loud for the lights to pulse like they should (to the point that the audio distorts and stuff). I'm pretty sure that at maximum volume the preamps give off 2 volts. There are only 2 solutions I can think of to fix this problem: 1. Buy more sensitive transistors, like ones that will let current through at say, 1 volt or 1/2 volt. 2. Amplify the signal coming from the preamps. I don't know what transistors to buy or how to amplify the signal, so if someone could tell me how to do that that would be great. Also, if you have a better suggestion lay it on me! And one more bonus question- if I ever wanted the lights to pulse in stereo, where could I put diodes to make that happen? Thanks!


Use an audio transformer

Part of me reply vanished  so I'll try again . Hook the 8 ohm leads of the RS transformer  and the 1000 ohm leads to your circuit. this will boost the signal voltage to the transistors, turning them on at lower volume.I would in fact put a 100 ohm resistor in the base lead of the transistors so you don't burn then out when you do crank up the volume. This also has the advantage of isolating the 12v nasties from your amp's output, no boom !! Hope this helps !!

Here is an easy solution. Go to Radio Shack & get 2

Audio Output Transformer  Catalog #: 273-1380

Use a LM386 Microchip to amplify the audio signal on the LED's, you will need two though to have both left and right speaker pulses and i only needed 2 1.5 volt batteries to power the microchips, you could also use 2 relays after the microchips and use your 12 volt source to power your leds, hope this helps

preamplify the audio signals prior to the transistor switches.

For more info on how to use transistors, check at radio shack for one of their handbooks of circuits or see


(I'd start with the introduction to transistors in the "Detailed Transistor Links" area

(that is, you could build a pair of little preamps using transistors to drive the base on the transistor switches...the link will teach you how)

We tried doing that, but nothing lit up when we tested it. This is what we did, does it look right?(it's possible the schematic is correct and we just hooked something up wrong) By the way thanks for your help everyone. Oh, and the reason I keep saying "we" is that the user codongolev is my brother, and we've been working on this together.

schematic of cco amp.jpg

i think the problem with your picture is that there shouldn't be a wire going from B on the left transistor to E on the left transistor. Try it just hooking C on the left to C on the right, and E on the left to B on the right. Then put your signal into B on the left, and have E on the right go to the leds. I think...

Replace your transistors with another stereo amplifier, use that to drive the LEDs. Steve

that seems kind of expensive, plus I think it would be too powerful... also I don't know the ohms of the leds... are there amps that could do that well that you know of?

Instead of transistors, make a little amp with an LM380 or LM386.

btw, we don't know why the lights don't pulse in stereo. (we're brothers, just so you know).

Swap the audio L/R - same problem or not? L

Well funny story about that... at one point while we were testing the circuit I accidentally put 12 volts into my iPod and now one ear doesn't work on it... hehe... but I can tell you this-it doesn't matter what side of the circuit is hooked up (they both work the same) and it doesn't matter what polarity I hook it up in (i can switch the inner wire and the outer layer and it works the same way) one curious thing though- if I hook left up to left on the circuit and right up to right(the right ear is the blown one) it simply stays on (it didn't do this before I blew the right ear on my iPod). However, if I hook it up the opposite way both sets of leds pulse with one ear. I have no idea why this happens.

Right so a defective iPod doesn't help. If that's what is driving this you've got a known problem there if nowhere else. L