Interesting Current Probe

Oh, the WRITE heads are inductive; that's the wire pair you want to connect to. If you can see it. And, if you can weld really small wires.

You can do that, but the MR gives you (iirc) about 60 dB more signal.

Cheers

Phil Hobbs

I'd be interested to see how it copes with multilayer PCBs.

A lot of the time, the current I'm interested in is in an inner layer.

"Tom Del Rosso" wrote in news:j6o8kd$91t$1 @dont-email.me:

I would advise to use read/write heads from an old floppy, they have a handy size, and wont break so easely. Also you dont need a magnifier glass to see them......

Why don't you just build one as in Figure E1? Does not look difficult. I doubt a HDD head is suitable for this at all.

Arno

But MR effect is proportional to |B|, not to a component of B-vector, so you'll get odd effects (frequency doubling). I'm more comfortable with a search coil type probe. Heck, it doesn't even need any ferrite. I've made several for o'scope use, somehow they keep getting borrowed; like when I was in college, and my seasoned castiron frypans always wandered off when a roommate left...

I asked first if it was theoretically feasible, so it doesn't make sense to tell me that it isn't but I should try it anyway, but next time I have a scrap drive I'll give it a shot.

Very good point indeed! I will ask the suppliers.

JB

Aehm, Figure E1 does not use a HDD head, i.e. I did not tell you to try anyways? Still, trying does nor hurt. But the comment that modern heads are magneto-resistive and hence do not use coils would at least require an adapted amplifier.

Arno

=20

I just scrapped a drive last month. Would you like the head stack?

?-)

Oh sorry. I Misread. Anyway it's interesting even when you learn you can't do something and why.

On 10 Oct 2011 19:31:25 GMT, Arno put finger to keyboard and composed:

Here is a collection of HDD preamp datasheets:

The VTC and Philips datasheets are the more informative ones.

Here are HDD Read Channel datasheets:

- Franc Zabkar