File:040612 diskhack.jpg

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crows_in_trees

Hmmm, interesting... what sort of hack is this? I have a couple of dead disks and am looking for things to do with them....

AЯMEN

This is interesting.

Greg Francke

Hi! It's a very simple controller: the 4 pins on the drive motor are 3 coils and one common- usually the resistance between any two coils is greater than the resistance of any coil to common, that way you can find which is which. The common pin can simply be connected to the (-) input on an opamp. Use a quad opamp, and connect each 'coil' pin to a (+) input. Spinning the platter makes enough differential voltage to change the state of the opamp, which then can control anything- I want to use it to control a 'walkman' sized analog synth; 2-3 voices and a filter+amp stage.

Greg Francke

In this foto the orange glow is from a vactrol controlling the filter- a 3 way toggle selects which 'coil' signal controls the LED making an 'auto wah' type effect for whatever signal the thing is controlling.

Greg Francke

The output from the coil is run through a 1k resistor to the input pin of the opamp; a 10k resistor connects the output pin of the opamp to the input pin, for a gain of 10, I think. It's bulletproof, I use a TLO84, but any quad opamp should work

crows_in_trees

Thanks for the explanations. Most harddrive hacks like the "HDDJ" involve PIC microcontrollers to determine speed & direction, but I don't want to get into that stuff yet. I'll probably try your way.

Greg Francke

Have fun! I mounted mine in a tupperware bin to hold pots & switches, etc while I figure out what it's exactly going to control.

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Source Flickr: 040612_diskhack
Author Greg Francke
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