Magnetic Data Reading Using the SX Chip

rizi

Hi,
I'm doing a project for a friend where I have to develop a swipe card security system and was wondering if·anyone·could help me build my project by setting me in the right direction.
The way our system is supposed to work is as follows:
Each member·carries a unique magnetic swipe card, that contains their password (along with other information) on track two of the stripe
When a member swipes his/her card s/he is prompted to enter their password.
If the password matches the one contained in the stripe, access is granted.
We are encouraged to use one chip in doing all this.
I called tech support and found out that I can do this using an SX chip. But just wanted to make sure that it would work.
Do you have any suggestions?
Your help in this matter would be greatly appreciated.
Thanks

stef

Hi

I'm working on a simmalar project but I'm using prximity cards. The card is realy no issue. Everything depends on the type of reader and is hardware connection it is using. A mag stripe reader is offen using a clock/data interface. A proximity reader is using DATA0/DATA1 interface. This latest i 'm using on a SX28. It is a simple protocol with some specific timing but it is easaly doable with an SX. I was also planning to implement the clock/data but I did not fount the time for it. If you are intrested I can send you some information on this. The wiegand is now a few weeks oparational on the sx.

Sarry for my englisch. My motherlanguage is DUTCH.



Best reguards

STef

rizi

Thanks a lot stef. I would really really appreciate if you could further help me out on this. Also, I'm trying to read directly from the head (2 wires right out of the head). Do you think that would be an issue?
My email address is knoknoc@hotmail.com
Please feel free to contact me.
Thanks

Bean

I don't think you'll have much luck reading directly from the head.
There is alot of analog circuitry used to condition the signals into digital pulses.

I would go with RFID cards anyway, you'll have alot less problems with them.

Bean.

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JonnyMac

All Electronics has an inexpensive card reader that you could use with the SX:

www.allelectronics.com/cgi-bin/item/MCR-12/search/MAGNETIC_CARD_READER_.html

If you don't want to go with a [noparse][[/noparse]possibly] used product, you can get new ones (more expensive) from Digi-Key:

dkc3.digikey.com/PDF/T071/1832.pdf

Post Edited (JonnyMac) : 1/30/2007 5:14:35 PM GMT

stef

Hi rizi

I'm seching my notes on the project i created to read proximity cards. If I find them I will send them to you tomorrow.

Second, I agree with Bean. It is too difficult to use the magnetic head direktly. Thier are a lot off readers on the market to take that job out of your hands. The interfaces are standard in accescontroleworld. They use a lot wiegand. I used for my project a HID reader(miniprox). I work in a company that was dismanteling a huge installation and they dumped the readerheads. So I started using that on.

I don't know where you are lokated but I have still some in spare. I you want some??(If it is possible)

The project I created is almost finiched. We are in finel test. We are readeing car numberplates with a videocamera. Extract the numberplate number and convert them to wiegand to send them to an accescontrole system. The conversionpart is don with an sx chip.
So yes it is possible with some finetuning.

Stef

Keith M

I played around with magnetic stripe readers for awhile. It was pretty fun decoding drivers licenses, credit cards, Dave & Busters cards and so on.

I bought a Magtek (see http://www.magtek.com/products/card_readers/mini/rs232/mini.asp ) mini rs-232 wedge. I hooked it up to my Palm Pilot and wrote some software that would read and store swiped cards. All the decoding circuitry was in the wedge, and the device spit out raw data. I do remember seeing DIY circuits from years past on making your own, so perhaps for RUDIMENTARY unreliable results, it may not impossible.

When you purchase a reader, make sure to note whether it will read the necessary track(you said track 2). The cheaper ones do not support all the tracks. Heck if I can remember off the top of my head, but one of the tracks was less popular. Maybe track 3? I'm not sure. In any event, I'd double check that before purchasing anything.

That magtek was pretty expensive (maybe $100), but it read a larger set of cards, not just based on number of tracks supported, but also other factors, like different coercivity cards, handling different swipe speeds well, and so on.

If you use this version (http://www.magtek.com/products/card_readers/mini/ttl/mini.asp) it spits out TTL, you could wire directly (maybe a series current limiting resister too) to an SX port.

When I was researching trying to read cards, I too, look at just using a head. It's not worth the trouble unless you are time-rich and money poor.

HTH,

Keith

Beau Schwabe

First let me say that I agree with everyone, that you are in for a learning experience trying to directly read the magnetic head of a
card reader.

However, I suspect that if one wanted to roll their own method of reading the magnetic head directly. The approach that I would
be inclined to take is to treat the head like a tuning coil. Set the head up as a series resonate device and find out what the resonate
frequency is of the head+tape (or head+card) by sweeping a known frequency range and monitoring a scope for any peaks. Once
you find a resonate frequency you will want to slightly back-off or detune from that frequency. Apply that frequency to the same L-C
configuration you used during the sweep, then any fluctuation on the magnetic media in the presence of the magnetic head should
generate large enough amplitude swings that a simple Op-Amp would be all you need. Depending on how well the circuit is "tuned"
you might be able to simply use the I/O threshold on the SX pin itself and drop the Op-Amp entirely.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.