I've got a partly working music visualizer, (6 band spectrum analyser) but there is a problem. I've investigated it thoroughly, but I don't know what to do about it.
Here's a schematic:
*The positive and negative inputs on the LM358 chips are backwards on the schematic
First, audio is sent to each notch bandpass filter (LM358). I got the circuit from here.
Next, the signal from each filter is sent to an LED driver, which powers 10 LEDs each.
The problem is, the three highest frequency filter-driver systems are always lit. The 8K is lit nearly all the way, while the 3K is at about half, and the 800 only just lit.
I've plugged my headphones into the output of each bandpass filter, and the highest three have some noise coming out of them (whether there is a signal going to the input or not). If I put music to the inputs of each filter, I can hear the right frequencies from the right filter (on the 8K, only highs, and the 100, only lows).
The three lowest frequency filters made no noticeable noise at all, and did not light the LEDs unless they had an audio signal coming in.
Although the LED drivers for the three highest are lit, the noise I hear from the filter outputs is much quieter than the sound that would normally light the drivers, therefore I suspect the sound lighting them is out of range of my hearing.
I isolated each bandpass filter from the circuit and listened to their outputs. I noticed that the highest frequency one made a high frequency noise, the second highest made a lower noise, and the third highest made the lowest noise of the three. It seems that having them all on the same circuit combines the noise.
On a probably related note, if I put my headphones in parallel with the audio input, I hear lots of noise from the bandpass filter along with the audio signal. It seems the noise is travelling back through the inputs of the filter (or looping back in some other way).
I've checked the two power supplies, (+5VDC and -5VDC) and they both create a fairly clean signal.
The audio signal come directly from a desktop sound card.
Here is an image of the breadboarded circuit, and here are the LED bars. Only the two highest and lowest (8K, 3K, 100, 30 from left to right) are hooked up in this image. Each LED bar is also upside down (a low signal would light the top few). The paint is chipped, but each LED will be covered by a diffuser, so it doesn't matter much.
I have an oscilloscope if someone needs some measurements.
Here's a schematic:
*The positive and negative inputs on the LM358 chips are backwards on the schematic
First, audio is sent to each notch bandpass filter (LM358). I got the circuit from here.
Next, the signal from each filter is sent to an LED driver, which powers 10 LEDs each.
The problem is, the three highest frequency filter-driver systems are always lit. The 8K is lit nearly all the way, while the 3K is at about half, and the 800 only just lit.
I've plugged my headphones into the output of each bandpass filter, and the highest three have some noise coming out of them (whether there is a signal going to the input or not). If I put music to the inputs of each filter, I can hear the right frequencies from the right filter (on the 8K, only highs, and the 100, only lows).
The three lowest frequency filters made no noticeable noise at all, and did not light the LEDs unless they had an audio signal coming in.
Although the LED drivers for the three highest are lit, the noise I hear from the filter outputs is much quieter than the sound that would normally light the drivers, therefore I suspect the sound lighting them is out of range of my hearing.
I isolated each bandpass filter from the circuit and listened to their outputs. I noticed that the highest frequency one made a high frequency noise, the second highest made a lower noise, and the third highest made the lowest noise of the three. It seems that having them all on the same circuit combines the noise.
On a probably related note, if I put my headphones in parallel with the audio input, I hear lots of noise from the bandpass filter along with the audio signal. It seems the noise is travelling back through the inputs of the filter (or looping back in some other way).
I've checked the two power supplies, (+5VDC and -5VDC) and they both create a fairly clean signal.
The audio signal come directly from a desktop sound card.
Here is an image of the breadboarded circuit, and here are the LED bars. Only the two highest and lowest (8K, 3K, 100, 30 from left to right) are hooked up in this image. Each LED bar is also upside down (a low signal would light the top few). The paint is chipped, but each LED will be covered by a diffuser, so it doesn't matter much.
I have an oscilloscope if someone needs some measurements.