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[DPRG] [DMS] Using HDD read/write heads as magnet sensors?

Subject: [DPRG] [DMS] Using HDD read/write heads as magnet sensors?
From: Chuck McManis cmcmanis at mcmanis.com
Date: Thu Oct 13 13:07:44 CDT 2011

On Tue, Oct 11, 2011 at 6:02 PM, Oguz Yetkin <oyetkin at gmail.com> wrote:

> I'm interested in the more recent sensors, which, to the best of my
> understanding, use Giant MagnetoResistance (GMR) effects to read the
> magnetism.
> What I don't know how to do is to interface with the electronics.  I
> suppose I'll have to rip out a read head or two and hook it up to a DAQ
> system with some applied voltage (which may, of course, prove to be naive).
>   You're probably right about the local sensitivity, which actually would be
> a plus for me.
> Which leaves me with the question:  does anyone have any hard drives
> (preferably recent) I can take apart? :)

The good news is that 'dead' drives are really really easy to find. Probably
any computer store, certainly and company of any size their IT department
will have some. The not so good news is that the driver for the read/write
heads is built into the servo control chip which is on the mainboard of the
disk drive and is a completely proprietary part. So what that leaves you
with if you take the leads directly from the disk arm is a fairly
sophsiticated pre-amplifier stage, probably a flash adc and a small DSP to
convert what the head 'can see' into something you can use.


> Oguz
> On Tue, Oct 11, 2011 at 7:38 PM, Jonathan Shook <jshook at gmail.com> wrote:
>> No, I have no experience with this, but I do have conjecture, for what
>> it's worth (not much).
>> I'm assuming:
>> It may may be sensitive, but the proximity to the disk is very important,
>> so that the local field bias has a greater influence on the read sensor than
>> ambient EMF.
>> The ability to detect field bias may be more useful than a large dynamic
>> range in the design of the read head.. so your applicability may be hit or
>> miss.
>> The sense time of the head has to be extremely low, suggesting extremely
>> low impedance, and likely a dependence on some very specially tuned sensing
>> logic/amplification.
>> BUT, I would suggest you ask Ben about this, because he is the most likely
>> expert among us.
>> On Tue, Oct 11, 2011 at 6:07 PM, Oguz Yetkin <oyetkin at gmail.com> wrote:
>>> Hello,
>>> It just dawned on me that the read/write had on a modern Hard Disk Drive
>>> might contain a more sensitive magnetism sensor than what I have been buying
>>> as separate components online (ratiometric Hall Effect sensors).
>>> Does anyone here have any experience reading from an old HD read head?
>>>  I've been searching the Arduino forums, etc. but most of what I've found
>>> concerns controlling the positioning of the heads
>>> These are the closest things I could find to 'useful'
>>> HDDJ: Turning an HDD into a rotary input device (involves reading the
>>> motor)
>>> http://www.instructables.com/id/HDDJ-Turning-an-old-hard-disk-drive-into-a-rotary/
>>> Involves controlling head positioning
>>> HD Laser Display
>>> http://spikenzielabs.com/SpikenzieLabs/Laser_Display.html
>>> HD Oscilloscope
>>> http://hackedgadgets.com/2006/04/25/top-5-uses-for-a-dead-hard-drive/2/
>>> As always, any help/insight is appreciated.
>>> Thanks,
>>> Oguz
>>> _______________________________________________
>>> DMS mailing list
>>> DMS at lists.dallasmakerspace.org
>>> http://lists.dallasmakerspace.org/listinfo/dms
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