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Author Topic: Help with magnetic reader head usage  (Read 4212 times)
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deveshsamaiya
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« on: September 29, 2012, 05:45:40 05:45 »

Hi,

I am working on this interesting project where i am trying to make a simple system using magnetic reader head (found in cassette players) along with a micro-controller to interpret the data and process it further.

My question is : What kind of circuitry do i need around magnetic reader head, so that i can read the spikes generated by magnetic read head on my micro controller.

Regarding micro controllers family, it can be anyone in MSP430, AVR, 8051, ARM7...

Please suggest some ideas for reading magnetic reader head properly, because with this hack we can easily make cool things around magnetic cards...

Image of magnetic reader head i am using is attached
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embedded@iit
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« Reply #1 on: September 29, 2012, 11:54:21 11:54 »

Did you bother to Google for a solution at all? Tons of hits.

You don't need a microcontroller - you can use your sound card and process it on your PC
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metal
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« Reply #2 on: September 29, 2012, 04:09:51 16:09 »

Expert answer: connect it to a voltage source, and oscilloscope, pass your tongue over it and see if you sense sth on your tongue, and keep looking at the oscilloscope till you see sth. Smiley Hopefully you will lose your tongue Wink
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« Reply #3 on: September 29, 2012, 05:07:16 17:07 »

Many years ago, when the giant reptiles walked the Earth, another gentleman and I built (at the time) what was considered a high security system using mag cards. (I'm saying my memory may be a little fuzzy.)

Look at MagTek's website. They used to have a lot of white papers discussing the technical side of things.

You will need an o'scope. Those magnetic heads vary in output to an incredible extent. Your project will not work without a scope.

Find powdered iron. (hobby shop, High school or college chem lab or (what I originally did) iron filings and a mortar and pestle. Get a bottle with an eyedropper, put some iron powder in it and fill the bottle with acetone or high concentration isopropyl alcohol. Shake it up and put a few drops on the back of the mag stripe card. Now you can see the magnetic tracks or even the magnetic transitions. Now you can see what you are doing.

We used a dual (or maybe it was a quad) op-amp and 4 (or 6?) AA batteries. Battery + was, obviously analog power +. Battery ground was analog - (negative supply) and digital ground. "center tap" of the batteries was analog ground. After the mag stripe signal was recovered and amplified, the 4th op-amp "shifted" it from negative to ground.

Keep in mind that as people swipe the card the card will move at different speeds and the magnetic transitions will not be a uniform width on the card because people accelerate the card as it moves through the reader. Most of the systems did not have "clock transitions" encoded on them because there wasn't enough space. So, we wrote some initial transitions and would count clock cycles between "start" and "end," and with a known pulse with of 1 and 0 we could calculate an initial "real width" for the particular person/card. That way, even if the card accelerated or decelerated, as long as a particular pulse was within "X" number of counts with our initial calculated time, we knew if it was a 1 or 0.

We used one of the TLxxx series op amps. I don't really remember the specifics, but a lot of heads would "saturate" if the card moved too fast and the output waveform would "collapse."

Of course, MagTek used to sell devices (ICs) that had power supply, amp, "discriminator" and such all on board a 16 or 18 pin device.

Well - it took us about a month to learn all that. You are welcome.

There are a couple books floating around in PDF format on using smart cards and mag stripe cards. There is also a really informative (old) file called "hacking mag stripe cards" or something like that that has a lot of good information in it.

Before I forget, everyone has the great idea about halfway through this project of using a couple transistors and a couple zener diodes to try to drive the microcontroller with a (maxed out) magnetic head signal, then try to square it off with the zener diodes because it's cheap. Don't bother. Doesn't work.

Good luck.


here's the file: http://www.hackcanada.com/ice3/card/phrack37-6.txt




« Last Edit: September 29, 2012, 05:16:29 17:16 by LabVIEWguru » Logged
bbarney
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« Reply #4 on: September 30, 2012, 01:01:50 01:01 »

Thank's LabVIEWguru
Metal alway's thought me & Pickit were the only ones to remember when the giant reptiles walked the Earth   Cheesy
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pickit2
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There is no evidence that I muted SoNsIvRi


« Reply #5 on: September 30, 2012, 02:18:18 02:18 »

Thank's LabVIEWguru
Metal alway's thought me & Pickit were the only ones to remember when the giant reptiles walked the Earth   Cheesy
And I still get the blame for killing then off, I only muted them, wait I think I can still unmute them,
damn where did I put that one bit memory key. damn oldtimers kicking in again.

In my place of work, we used to have swipe cards for the vending machines, out of devilment we soon was able to charge them with any amount of credit, same for the old phone cards.
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Note: If you have no posts other than, I want or reporting a dead link Then you can't complain If I remove your post So Stop Leeching
borberk
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« Reply #6 on: September 30, 2012, 03:24:08 15:24 »

Spectrum computer from year 83 was using ordinary audio cassete to save or load programs. Usual cassete player was used. I had Grundig C410. Schematics are available here:
http://elektrotanya.com/grundig_c410.rar/download.html

Head output voltage is abt. 1mV or less so following low noise amplifier must have high gain and AGC too.
« Last Edit: September 30, 2012, 03:27:15 15:27 by borberk » Logged
bbarney
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« Reply #7 on: September 30, 2012, 03:33:35 15:33 »

So did a Commadore Vic20 and the Commadore 64
« Last Edit: September 30, 2012, 03:36:45 15:36 by bbarney » Logged

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« Reply #8 on: October 03, 2012, 04:00:55 04:00 »

>Metal alway's thought me & Pickit were the only ones to remember when the giant reptiles walked the Earth<
You are welcome!

I tried to build the Mark8 etching my own boards using a sunlamp. I bought an extra magazine, then sent off for the book. I soaked the PC board plots in vegetable oil to make it "almost" transparent, then put under the sunlamp. Those were dinosaur days.

>And I still get the blame for killing then off,<
Well, you missed a few. I have a sister-in-law that could snap your balls off before consuming the rest of your carcase.

>In my place of work, we used to have swipe cards for the vending machines..<
See, that was cool. Nobody did it to be a criminal (well, not much of one) you just did it to see who was smarter - to "hack" the system. Those were fun days.....




For deveshsamaiya:

AN727 - Credit Card Reader Using a PIC12C509 (Microchip)
PSoC 5 as a Magnetic Card Reader (Cypress Semiconductor)
I/O INTERFACE FOR TTL MAGNETIC STRIPE READERS TECHNICAL REFERENCE MANUAL (MAGTEK)
99800004-1.03.pdf - Magnetic Stripe Card Standards (MAGTEK)
MAGNETIC CARD READER DESIGN KIT TECHNICAL SPECIFICATION Part Number: 99821002 Rev 20 (MAGTEK)

I have got a book on Mag stripe readers, I've been looking for it and when I find it I'll post a link
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gan_canny
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« Reply #9 on: October 03, 2012, 10:50:37 10:50 »

I remember in the  70's using a cassette recorder to install a program into ram for my home built  computer (prior to the TRS80). It had issues but it sure beat toggling in the machine code. An audio head is used in the linear region of the heads magnetic hysteresis. For digital NRZ is often used where saturated  North and South poles are forced onto the tape and the linear region avoided.The other issue was the cassette tapes aren't that good; often having missing magnetic spots that reduce the quality of the audio in a technical sense but not so much that the human ear could detect. With digital a single drop of a 1 or 0 was a problem so a fault correction algorithm was employed.
« Last Edit: October 03, 2012, 10:55:09 10:55 by gan_canny » Logged
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« Reply #10 on: October 04, 2012, 12:11:57 00:11 »

"I'll take the category 'Things that only old computer geeks know for 10,000 dollars."

What was the format called that the audio was recorded in, and why?

If you look it up, you are automatically disqualified!
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Magnox
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« Reply #11 on: October 04, 2012, 09:34:44 09:34 »

I KNOW, I KNOW!!! (OK, I'll sit down now)

I remember the days of listening to the sweet, sweet music of digital data as my Speccy (the original rubber one) loaded up my assembler, or perhaps Jet Set Willy.

Doing tape-to-tape back-ups to a 90 minute TDK chrome, and swearing when the recorder chewed the tape.

Starting a program loading, then going and making a sandwich will it bleeped and screeched along to itself. Sometimes I would finish eating the sandwich before the program was ready.

Oh, the answer? Well, technically it would be frequency shift keying I think, a burst of one note for a one, and another note for a zero. 2400Hz and 1200Hz, although my speccy didn't quite follow the standard (it was old even by then).

The name? Named after one of the first, and best, computer and electronic magazines. Byte standard (I think) because they held a meeting, the result of which was the format.

(My first-used 'real' computer was a DEC PDP-11/34 running RSTS/E. It did have a card reader attached (that's punched card for the newbies, not smart card)
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bytraper
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« Reply #12 on: October 18, 2012, 10:39:33 10:39 »

Have you tried playing with a 10 bit A/D converter in a pic or avr ?
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