Spectrum Analyzer; Is this even possible

[pcman2002b]

Here is what I want to do.
I have a hard drive that I took apart, everything works mechanical wise (heads and spindle motor). I have the thing spinning inside my computer with the top off just something neat to look at with the lights shining on it. What I thought would be cool, is make a spectrum analyzer out of the heads. A very basic one at best, when the beat of a song or something occured the head would move to the center and with the abscence of sound it would return to the outside edge (or vice versa). I've already traced the leads for the electro magnet on the head and have been able to get them to work by hooking them up to a 9-volt battery and switching the polarity back and forth causing the heads to move in and out. Is this even possible and if so how easy or complicated would it be. I don't care about KHz and frequencies causing the heads to stop in different positions just center and out (two positions).

Also one more quick question. Is there some electronic device that can be used to at a set time switch polarity from one to the other. Some small trinket that makes the polarity switch maybe every 5 seconds or something.

Thanks in advance.

 

[f95toli]

I have seen simple "spectrum analyzer" ICs (I guess they are made for home audio) which could work.
Another way would of course be to use a bunch of op-amps and build active filters, one filter for each head.

 

[Train]

youd have to get into the driver level programming of your specific hard drive, thats where (i think, not sure) you can actually send istructions to the HD telling it to look at a low block (near the outside of the disk) or to its highest blocks (near the inside) and just tie that into your sound card, winamp, whatever equalizer and whenever a high frequncy note hits, tell the HD to look high, then when a low beat hits, tell it to look low. Sounds like a cool idea

 

[Mark R]

Try getting an audio amplifier, and connecting the speaker outputs to the head-actuator coil.

This should work fine with a hi-fi amp, if you keep the volume really low - but better to experiment with a POS set of PC speakers. Find the 'slave' speaker, cut it off and attach the wires to the head coil.

Should do something similar to what you want.

 

[f95toli]

Originally posted by: Mark R
Try getting an audio amplifier, and connecting the speaker outputs to the head-actuator coil. This should work fine with a hi-fi amp, if you keep the volume really low - but better to experiment with a POS set of PC speakers. Find the 'slave' speaker, cut it off and attach the wires to the head coil. Should do something similar to what you want.

Then the head would move when the volume changes. I thought the point was to get the heads to move when the frequency content in each band changes? Otherwise it is not a spectrum analyzer.

 

[hakadate]

Please some one explain to me how any of this has to do with spectram analysis or to be a

Spectrum Analyzer.

 

[Menelaos]

hakadate,

This indeed is a misuse of the term spectrum analyser.

What he's pointing to is the graphical indication of the frequencies of an audio signal. These incorporate only a discrete set of frequencies. A real spectrum analyser sweeps a range of frequencies and determines there relative output power.

As for the actuator circuit:

Use a low-pass filter (<150-300Hz), possibly followed by a comparator to set the correct voltage levels for the actuator.

Hope this helps,

Menel.

 

[spikemike]

I would go with the lowpass filter idea. Its just a simple capacitor and resistor and then hook the output to one of the heads and branch off the output of the filter to an inverter and the output of the inverter to another head so if one head is one the other will be on. I'm not sure if i quite understand it but this would be an easy way to turn 1 thing on if it is low and turn another thing on if it is high.

 

[Bleep]

just get a ne555 timer chip at radio shack for about two bits. Switch a floating loop PS with it.

Bleep