Magnetic Field of Money/How to read it

Hello, I am currently doing a senior project which part of it requires me to read the magnetic field of the ink on United States currency. One ideal I had was to use the reader of tape player to try and measure the magnetic field. This is where the problem occurs. I am not exactly sure how this reader works, I have tried to ohm the wires out to see if one is a reader and one is write. I have also tried to hook up a simple op-amp gain circuit of 100 to raise any signal that comes out of this, but mainly all I get is noise on my scope. So my questions are;

  1. Is the tape player head sensitive enough to pick up the magnetic field of money?
  2. How exactly do these heads work? (I know you have to pass it over the field)

Also I am open to suggestions to otherwise measure the magnetic field...Keep in mind that cost is an issue, since this project is mainly getting funded out of my pocket. Thanks in advance for any help!

Reply to
joshs2004
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Good Luck! Rich

Reply to
Rich Grise

Um, I am not trying to read a strip from a credit card or the likes. I am trying to read the magnetic field of U.S Currency, as the money is printed with magnetic ink. Many vending machines/money changer have this technology.

Reply to
joshs2004

snipped-for-privacy@gmail.com hath wroth:

How do you expect to learn anything if we do all your homework and your senior project for you? Did you really go through 4+ years of college to culminate it with someone elses work? For this you expect a diploma?

All of your questions are answerable with fairly simple Google searches of the terms you've presented. You should be able to handle that yourself. Find out how big a magnetic field your currency is producing. Then find a sensor that's suitable. I think you'll find a recording head to be rather insensitive.

I'll make it easy for you. First hit from Google search for "magnetic field of money". The Color of Money: Using Magnetic Media Detection to Identify Currency Lots of numbers and hints to play with. The fun will be in building it.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Reply to
Jeff Liebermann

The principle is the same.

Magnet field on paper is the same as magnetic tape.

don

PS: Good Luck, you will need it.

Reply to
Donald

There is detection of magnetic material and the decoding of magnetic content. While the both use magnetism, there are differences.

Decoding Magnetic content is based on a technology known as MICR - Magnetic Ink Character Recognition. The primary use was for automated systems that read the information coded on bank checks so they could be cleared and routed back to the source. It is now used in some Point of Sale systems to read account information from franked checks.

Unlike credit cards which use bands of alternately aligned magnetic fields, MICR works by signature recognition. The bank check MICR used uniquely formed characters that would produce unique output waveforms when passed over a magnetic read head. There is a published specification available for MICR. They key to MICR is to move the media containing the magnetic encoded information across a single magnetic read head. By moving the media, the static magnetic field now becomes a time varying magnetic field which can be detected by the magnetic read head. With a constant velocity, each character will produce a unique waveform (signature) as it moves by.

A quick Google search came up with a FAQ that does show some of the waveforms for various shapes.

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Money is printed with Magnetic Ink. Regions of heavy inking such as the borders will actually cause deflection in the presence of a strong magnetic field. The US Treasury can provide the details of where and how the magnetic fields are designed Since this is a anti- counterfieting measure, the specification is probably not in the public domain, nor readily available.

If I were experimenting with this, I would procur a used Point of Sale printer such as an IBM 4610-TI4 or Axiohm A758 with MICR capabilities

- or you could get a standalone MICR reader such as a MagTek - from eBay. This will set you back about $ 50. You may find a local company that does Point of Sale repair and get a clunker from them. If you get an RS-232 printer, you can simply send it a command to start a MICR read, or in the case of the MagTek unit, just insert the paper item. This will cause an inserted piece of paper to be pulled into the unit at a constant speed over the internal magnetic read head. This position of the head is fixed and set to align with account number fields at the bottom of the checks. With this as your base, you could add another tape head to experiment with reading other portions of a dollar bill. You can then put a scope on the signal coming out of the tape head and begin your investigative work from there.

Regards,

Blakely

-- Blakely LaCroix Minneapolis, Minnesota

Reply to
Electroniker

A point I didn't see made very well in the other replies (though perhaps it was and I just missed it): When you are reading magnetic tape or stripes, you're reading something that's magnetized on purpose, and in fact magnetized in alternating directions as you move along the axis of the tape or stripe. When you are reading magnetic ink characters or the magnetic signature of paper money, you're reading something that may carry very little residual magnetism, and in general won't be magnetized in alternating directions as you scan. In the case of the tape or stripe, there isn't a significant change in the magnetic "impedance" around the sensor loop, but in the second, that's specifically what you are looking for: differences between the presence and absence of magnetic material in the path. So the first will generate a signal in a "passive" tape head, but the second requires some "excitation." It's rather like the different kind of sensor used to detect a spinning magnet versus the kind used to sense unmagnetized cog teeth. If you put "variable reluctance" into a search for magnetic sensors, you may come up with some useful stuff.

Cheers, Tom

Reply to
Tom Bruhns

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