Attend XDA's Second Annual Developer Conference, XDA:DevCon 2014!
5,811,404 Members 48,514 Now Online
XDA Developers Android and Mobile Development Forum

How do mobile card readers work?

Tip us?
 
resinis
Old
#1  
Senior Member - OP
Thanks Meter 24
Posts: 121
Join Date: Dec 2007
Phone How do mobile card readers work?

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
 
h33x
Old
#2  
Member
Thanks Meter 54
Posts: 58
Join Date: Oct 2013
Location: Novosibirsk
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.
 
ecparts
Old
#3  
Junior Member
Thanks Meter 0
Posts: 15
Join Date: Feb 2014
Your SIM Card has a chip, this chip can react by inserting the SIM Card slot.
 
Ryccardo
Old
#4  
Senior Member
Thanks Meter 123
Posts: 440
Join Date: Nov 2013
Location: Imola

 
DONATE TO ME
Quote:
Originally Posted by h33x View Post
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
Motorola International 8700 (first phone sold in Italy to send SMS) [half bricked] > Acer ? [returned] > Siemens S35i [good] > Samsung SGH-? [stolen] > Nokia 3220 [mostly still OK] > Motorola RAZR [still OK] > iPhone 3G S [2 batteries worn out] > iPhone 4S [I gave up after iOS 7, still has 10 months of warranty] > Samsung Ace 2 i8160 [won at Samsung giveaway, still works fine, CM10.1] > Sony Xperia U [modified Sony 2.3.7]
 
Renate NST
Old
#5  
Renate NST's Avatar
Recognized Contributor / Recognized Developer
Thanks Meter 804
Posts: 1,993
Join Date: Feb 2012
Location: Boston
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.

Tags
card reader, mobile credit card, paypal, paypal here
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes