ac voltage to 12v dc light intensity

[jasong]

i am trying to build a circuit that will have a light that brightens to the bass in my car audio. i don't want to use db sensors because they pick up all noises and i just want lighting to change to bass. i was thinking of using the varying ac audio signal that goes from the amp to the subs. the signal ranges from 0vac(no bass) to 40 vac (subs are hitting with greatest db readings). i could use the amp to power ac lighting but that would divert power from the subs and the apms efficiency will decrease. the leds will be powered from the cars battery. every circuit that i think of will just turn on and off. my first though was to use an scr. the gate will be turned on by the signal reaching some level set by a reostat allowing a 12 vdc current to flow which would power the lights, once again i believe this circuit will just turn on and off. i want my lights to dim and brighten to a 0-40 vac signal. any ideas.

 

[tcmtech]

I have done a simple set up like that years ago. I just used a basic optical coupler that was set up to be ran off the speaker line though a resistor and a pot in order to calibrate it. The optical coupler output side was a standard transistor type that was used to drive a Mosfet.
When the speaker line wave voltage exceeded the turn on voltage of the Opto coupler the Mosfet would turn on and provide power to the bulb. When the speaker line voltage dropped below the turn on point the Mosfet shut off and the power to the light stopped.

It was a simple and crude voltage to PWM signal converter of sorts. A little power only had short peaks above the turn on point and produced dim flashes while high volume gave long durations resulting in full brightness with small flickers proportional to the sound. The potentiometer was needed for adjusting the point the Opto coupler would start to conduct at and gave a good level adjustment method.

There are far more complicated ways of doing it also. This is just a very basic way that will work with minimal components and set up time.

 

[marcbarker]

Just connect a light bulb across the speaker.

 

[jasong]

i like the first reply and will probably try to build it and then fail. the second one sounds so easy and simple. is there a light bulb that can be powered by an ac signal that varies from 20-200 hz and 0-40 volts that will dim to brighten.

 

[audioguru]

A light bulb is almost a dead short when cool and might blow up the amplifier.
You need a rectifier circuit and lowpass filter to pass the bass and reject the higher frequencies.

Look in Google for Color Organ Circuit which usually has a driver for low frequencies, a driver for mid frequencies and a driver for high frequencies.

 

[Hero999]

Use LEDs rather than an incandescent.

I'd recommend a bridge rectifier with LEDs on the DC side with a suitable choke on the input to both limit the current and suppress high frequencies. A series resistor might also be a good idea but you'll need to take the impedance of the inductor into account.

 

[marcbarker]

Light bulb is fine trust me. If an amplifier hasn't got overload protection it shouldn't be in the consumer market. Try various household 110 V lamps to get a feel for the effect. You can also use a couple of 24 V bulbs in series, naturally, the more the bulb wattage, the more it loads the amplifier.

Speaker-powered LEDs are another way, and you don't get the cold start ohmage thing that audioguru mentioned. the cold start ohmage thing is an essential part of the light bulb, it's what make your light bulb go 'plink' and fail when you switch it on. Until LEDs can do this (or degrade another way) they will never catch on as room lights.

I don't think you need bother with filtering, because the sub bass unit is low frequencies anyway.

 

[Hero999]

an amplifier hasn't got overload protection it shouldn't be in the consumer market.

If the current limiting kicks in every time the bulb lights, the amplifier will clip causing poor bass response and harmonic distortion. I think LEDs are a much more sensible option.

hing is an essential part of the light bulb, it's what make your light bulb go 'plink' and fail when you switch it on. Until LEDs can do this (or degrade another way) they will never catch on as room lights.

Why, surely LEDs will catch on sooner because they have alonger life - that's one of their greated selling points.

 

[marcbarker]

If an LED room light lasts too long it's bad, because there wouldn't be anything to replace when the bulb fails. Manufacturers are probably searching for some reliable technology they can use to ensure that the LED lamp retains the authentic traditional incandescent experience.

Don't forget, the light bulb cold resistance is only present when the light bulb is cold. Light bulbs only go 'plink' when they are cold, and that would be when the first song starts.

 

[Hero999]

If an LED room light lasts too long it's bad, because there wouldn't be anything to replace when the bulb fails. Manufacturers are probably searching for some reliable technology they can use to ensure that the LED lamp retains the authentic traditional incandescent experience.

Sorry but I think that's nonsense.

Compact fluorescents, last at least five times as long as incandescents (now banned in some countries) are already replacing them. People mainly don't like compact fluorescents because they take awhile to warm up and the colour rendering isn't as good as incandescents.

When LEDs become brighter, more efficient than CFLs and the price drops enough people will start using them. Governments may even ban both fluorescents (which contain mercury) as well as inefficient incandescents.

 

[jasong]

i think the rectifier and leds is my best option, they use way less power assuming i use the amp to power the lights. i would like to use the car's power and the amp's power. i don't want to distort sound because the amp is designed to power low resistance loads with minimal distortion. i also will look like a retard to anyone who knows car audio for using the amp to power anything besides the subs. i'm still looking for a way to use a turn on circuit powered from the car's battery with the turn on signal to a base or gate from the amps output. im thinking a simple transisor/potentiometer circuit will do the trick unless anyone else has suggestions.

 

[marcbarker]

When LEDs become brighter, more efficient than CFLs and the price drops enough people will start using them.

But the light going 'plink' when we first switch it on, is an essential part of the Light Bulb Experience, and enjoyed by the whole of mankind. Until the manufacturers can design an LED that does that, it won't be real.

An LED room lamp that doesn't fail is also bad news. Once the market is saturated, the only way to maintain sales of LED room lamps would be to be building more and more buildings to take them, totally the opposite of reducing carbon foot print.

And most importantly, if bulbs never failed, what will happen to all the "Light Bulb" jokes?

PS, rectifier and LEDs sounds to me a best scheme. Maybe Luxeon LED can be used

 

[Hero999]

What nonsense, there are plenty of things that very rarely fail, yet there's still a market for them.

EDIT:
You're joking of course.

 

[marcbarker]

You're joking of course.

Of course

BTW It's difficult to imagine the home light fixture with a "non-user-serviceable-parts" label on it. Manfacturers would have to find some other way of planned obsolescence in lieu of a tungsten filament.

 

[RODALCO]

CFL's do last very long, my first Philips CSL failed after 18000 hours. (not bad)

 

[marcbarker]

CFL's do last very long, my first Philips CSL failed after 18000 hours. (not bad)

One of the 2 CFLs that I bought from IKEA FAILED after only 2 weeks!

 

[RODALCO]

Not good at all, demand your money back.

What manufacturer ?

 

[RODALCO]

Philips CFL

Photo's attached.

It was actually even more, 19440 hours

not bad at all.

 

[marcbarker]

Not good at all, demand your money back.

What manufacturer ?

I bought twin-pack of them last time I was in Spain, the other one hasn't failed. Anyway I feel better putting the word IKEA in bigger letters.

Probably made in China, the cheapest, like most all of ikea stuff.

 

[tariq7868]

how abt making simple RC lowpasss filter just as audiogru suggested .. this looks alot simpler...