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How do mobile card readers work?

18th December 2013, 10:20 AM   |  #1  
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This is driving me insane. I search everywhere on google and every single hit is the same thing. It says "click here! this is how mobile card readers work! just plug into your audio output and poof magic happens!"

I KNOOWW!! you plug it in. no kidding.

what I want to know is HOW does this thing actually work... how do you input data through a headphone jack?

On Paypals site, it says a microphone enabled phone is required... OK... so does the reader read the card, and then send encrypted tones to the microphone to be decoded like dial up internet?

Then what is the headphone jack for, power? how does the card reader get juice?

Driving me crazy that I cannot find a single site that actually explains it. They all just explain how to use them... is this what our world is coming to? dont worry how it works just trust it?

this is what im talking about- https://www.paypal.com/webapps/mpp/credit-card-reader
16th January 2014, 03:38 AM   |  #2  
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Hi! Don't worry, all is simple. Cardreader work as old tape recorder, you can find elementary scheme for it. Inside - tape head and some electronic components. And read smart card with magnet line standards.
1st March 2014, 12:03 PM   |  #3  
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Your SIM Card has a chip, this chip can react by inserting the SIM Card slot.
1st March 2014, 04:47 PM   |  #4  
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Quote:
Originally Posted by h33x

Hi! Don't worry, all is simple. Cardreader work as old tape recorder, you can find elementary scheme for it. Inside - tape head and some electronic components. And read smart card with magnet line standards.

Correct, like IrDA to audio adapters
2nd March 2014, 02:25 AM   |  #5  
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Yes, US standard magstripe credit cards are pretty primitive.
You only need to read a single track.

Microphones (in a PC or a cell phone) get a nominal 2.5V to power a FET preamp for an electret mic.
I'll bet the signal out of one of those card reader adapters is strong enough that they don't even need to use a preamp.
I think it's just a head in there very similar to what you would have found in a cassette player.
The next time you see a store card swiper, see if you can look inside at the right angle.
They are the same kind of head.

I used to use a 38.4 kHz IR receiver module (powered) run into a audio line input.
I could analyze IR remote signals.
The software is not that different.

The next junk day I'll look for a cassette player to savage and cobble up a card reader.
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