You can tell from the subject line that I have no idea what I'm talking about hahaha. Basically, I have to build a circuit that contains three LEDs. Each LED will respond to a specific range of frequency of an input signal(a song). My question is how can I get all the frequencies of a song and use them as the input signal for my circuit? Thanks!

 

You can tell from the subject line that I have no idea what I'm talking about hahaha. Basically, I have to build a circuit that contains three LEDs. Each LED will respond to a specific range of frequency of an input signal(a song). My question is how can I get all the frequencies of a song and use them as the input signal for my circuit? Thanks!

You just feed the input into one point.

You need to build a "band pass" filter for each of your target frequencies. The output can drive the LED directly or you can manipulate the output more.

 

You just feed the input into one point.

You need to build a "band pass" filter for each of your target frequencies. The output can drive the LED directly or you can manipulate the output more.

Hi GopherT,

Thanks for your prompt response. So I don't need to do anything fancy with the signal? My circuit currently has 3 second order op amps filters. One of the requirements is the circuit must operate independently from the volume or amplitude of the signal. Do you think this would work?

 

Hi GopherT,

Thanks for your prompt response. So I don't need to do anything fancy with the signal? My circuit currently has 3 second order op amps filters. One of the requirements is the circuit must operate independently from the volume or amplitude of the signal. Do you think this would work?

Maybe you should post a scematic.

 

Maybe you should post a scematic.

Sorry I don't have my computer with me at the moment. The circuit has the three filters connected in parallel. Each branch has an LED connected in series.

 

Sorry I don't have my computer with me at the moment. The circuit has the three filters connected in parallel. Each branch has an LED connected in series.

You may need an amplifier (op amp) at the output of each filter. That will make sure the LED turns on when some signal gets through the filter.

 

Music has a very wide range of amplitude. You need to stabilize the amplitude to get consistent results. Either add a volume control or an amplifier and a volume control, or even an automatic gain control circuit, then an amplifier. Why am I going on so much about this? Because you gave no clues about what amplitude of signal you want to work with. Start there. Bandpass filters only work with what they are given so you have to give them something they expect.

 

What you are looking for I think is LED color organ. Sorry on the phone so I cant supply a schematic...

 

Music has a very wide range of amplitude. You need to stabilize the amplitude to get consistent results.

I built a Heathkit color organ back in the 80's. When the music went louder(amplitude) that frequency's color also when brighter. Though the color organ used grain of wheat/mini christmas light strings not LEDs. One of the best color organ songs was "miss america" by Styx

 

Music has a very wide range of amplitude. You need to stabilize the amplitude to get consistent results. Either add a volume control or an amplifier and a volume control, or even an automatic gain control circuit, then an amplifier. Why am I going on so much about this? Because you gave no clues about what amplitude of signal you want to work with. Start there. Bandpass filters only work with what they are given so you have to give them something they expect.

Hi #12,

Thank you for your input. What you suggested was part of what I wanted to ask in the original post which was how to find the frequency range of a song. My plan is to have the three filters covered the whole range of the song evenly.

Sorry if I provided little to no info. This is a 3 month independent project for my ECE class and we're still learning about filters. I was trying to step a head and got stuck at the audio input part. What've been suggested here are very helpful. I actually have something to look up on Google now hahaha.

Thanks

 

What you suggested was part of what I wanted to ask in the original post

So...take a stab at it. Do you want to use a millivolt level from an AM band crystal radio? Vaguely 1 volt from from the, "line out" jack on an amplifier? Nearly ten volts from the speaker terminals of something driven with 10 watts of power? I just listed a range of 1,000 to 1 in voltages. You have to narrow that down to build a filter.