I almost have the circuit done. I am missing 5 switches, an expansion port, and storage memory. I was originally going to have a bar code reader on the same board but the size of the parts and the positioning of the IR stuff would have been a pain. So, I am going to add a tiny header to the board to allow hacking of all kinds. Since only 1-2 cogs will be used for the whole circuit why not allow hacking fun? You will notice I opted to use almost all SMD components in the design. Sorry if you feel your soldering skills are not up to the task, but the goal was to keep this all pocket-sized.
Background:
Originally I wanted to “spoof” RFID chips from my phone. After much looking into, even if I used ultra small parts, adding a spoofer into my phone became a little unrealistic. The best option turned out to be to solder a transistor to the headphone output jack and use pulse-width modulation to short the tuned circuit (lc) circuit. I wasn’t too keen on possible interference to my headphone jack. The other option was to fit the circuit into a 1/8 headphone jack, but then I would have something sticking out, and that wouldn’t be cool!
Phase 1:
I first used a simple RFID reader circuit I got for 10 bucks but found I was unable to read my work RFID card. After some looking around for better readers that support FSK and not just ASK, I came across a wonderful little circuit by Beth Scott. This used the propeller with a few extra parts. What I really liked about the design is the built-in tuner. The circuit looks like an inductor sensor with an attached LC. After building this and two failed coils I changed some of the capacitors around and lowered the mH of the inductor. This allowed me to complete 3 coils: 6 inch, 4inch, and 2 inch. Now I could read the cards!
Phase 2:
Still I needed to replay the payload. As luck would have it, Beth Scott released an awesome RFID tag using an Attiny85. While I could shrink her design down to be almost no bigger than the chip itself, the problem was how to reprogram it on the fly. Without finding any good answers or none that looked pretty phase 3 came in.
Phase 3:
With the reader outputting over a serial connection to my computer it was not very portable. At first I was going to use a simple 2 line character LCD that was lying around. To make sure I could really shrink Beth’s RFID tag down to the size of the chip, I needed an AVR programmer. Enter another nerd nip favorite of mine. Lady Ada owns a cool little site with all kinds of goodies at www.adafruit.com. While looking for an AVR programmer (I bought the AVRTinsy kit). I remembered the Nokia LCD screens are hacker approved. That completed my order from Ada Fruit. After getting the screen I was like hrmm…………….I bet I can make this whole circuit board with reader/spoofer fit on the back of the LCD! After some designs and a few test prints on paper, I was right: I could fit all the parts on the back of the LCD screen.
Phase 4:
With a lot of over-powered goodness I decided to remove some extra bloat from my wallet. I started to write a bar code library to draw my bar codes on the Nokia 5110 screen so I can ditch the plastic cards. I thought HEY! Why not add a bar code reader also and make this really awesome. Well, the circuit was just a little too big, and really, reading bar codes on the fly is something you do once. So, I created a bar code reader daughter board for the overall project.
About the Current Circuit:
The other night via Twitter I posted to @scanlime a sample schematic (Shown below). On the left side is the power supply with a green diode to let you know it’s on. The main center square is all the parts for the propeller chip (Memory, prop plug port, 5mhz crystal, and the propeller chip). Below that is a simple LC with a transistor to short on the circuit at the right times. Top right is the Nokia 5110 header. Below the Nokia 5110 Header is Beth Scott’s reader design. Missing additions to her design is two solid-state relays. These relays are made to shut off the inductor coil when the device is “spoof” mode. I am going to add 1mb-8mb of memory on board for storing the screen art, RFID tags, and bar codes. I think I have some Microchip flash memory some place that I will probably use. The memory will auto store via the readers or can be accessed via the prop plug’s serial connection. Two buttons below the LCD will change from reader to spoofer. On the side of the LCD will be an up and down buttons to scroll through a list RFID and bar codes. The PCB (once its been tested), will be made all open source goodness, and you will be able to order a print from http://batchpcb.com/ of course for free. I have no interest in selling circuits or parts. If it becomes popular, you can bug the lovely Lady Ada, and maybe she will sell a kit on her site. I also plan to make a home-brew friendly through-hole design that will be laser-printer friendly and single-sided. Attached below are some photos!
Links
Scanlime – Beth Scott
Lady Ada
Ada Fruit
. 
