ISO standards don't talk about that level, because it's not relevant
to the standard.

The standard is about the data, not the recording process.

To record today's hi-co cards, you'll need about 700 gauss to saturate the tape.
That is completely dependent on the head design, and you probably
won't have access to that data. So, one practical way to do it, is to
start with a square wave at roughly the correct BPI density (dependent
on card speed) and ramp up the drive current till the waveform when
you read the card, dosen't get any higher, indicating that the tape
has saturated.
Going more than that dosen't serve any purpose.



On 5/22/07, PAUL James <James.Paul@colibrys.com> wrote:
>
> Thanks Robert,
>
>  I now have enough info to start working on this.  I'll let you know how
> it all goes as soon as it's done.
>
>  TTYL,
>
>
>
> Regards,
>
>
> Jim
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Robert Rolf
> Sent: Tuesday, May 22, 2007 3:16 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [ENG]: Mag Stripe Recording Head Drive Signal
>
>
>
> PAUL James wrote:
> > All,
> >
> > I am wondering if anyone here knows anything about the amount of
> > drivre signal that needs to be fed to a Magnetic Stripe Recording Head
>
> > to allow it to record onto a magnetic substance similar in properties
> > to the magnetic stripe like on the back of credit cards or ID cards,
> etc.?
> >
> > I want to use a mag card head because of the mounting mechanism on the
>
> > head itself.  I plan to record onto a piece of paper that has metallic
>
> > particles glued to it's surface.  If this works like I want it to, I
> > can put together a demonstration that will be interesting for all.
> >
> > I've checked the web, and have found the ISO standards that are
> > followed by the Mag Card industry, but I don't see mention of the
> > signal strength to apply to the recording head anywhere in those
> > documents.  Unless I missed it, this info just isn't there.
> >
> > This is for a demonstration and possible utilization later, but in no
> > way do I have anything illegal planned for this unit.  It's mostly to
> > prove a point to myself, and to a couple of skeptic brothers-in-law
> > that think they have it figured out that this won't work.  I plan to
> > prove them wrong.
> >
> > If anyone has this info, I would appreciate hearing it.     You can
> > reply offline to me at jim@jpes.com.
>
> But the whole POINT of the piclist is to share such information.
>
> The write current will be a function of the particular magnetic head.
> Typically a few milliamps but you really should contact the manufacturer
> to be certain.
> 5V drive is common for card heads, but you can always start with lower
> current (it's inductive so current mode drive works better over a large
> frequency
> range) and work your way up until you're erasing existing data
> (saturation recording).
>
> Linear audio heads have 80V of 60kHz bias applied, but the audio drive
> is only a few volts there as well (much higher head impedance).
>
> There is a very old (1980s?) book called "Magnetic Recording" which has
> a huge amount of information on this 'ancient' technology.
>
> Robert
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