DIY
CIRCUITS
BREAKING AND ENTERING
Open and repair a damaged proximity
swipe card. By Graham Cattley
It all started one day at work. I had used my swipe
card to get through the front doors, and without
thinking too much, I put it in my back pocket. Later
that day I sat down — crunch! The card had cracked
from side to side. I wrapped it in tape to hold it
together, and it still worked for two weeks, but then
something in it failed. I tailgated people in and out of
the building that day.
Photography by Ed Troxell
I had paid my company a $100 deposit on that
pass card, and that night I decided I wasn’t going to
give it up by asking HR for a new one. I was determined to fix it myself.
A bit of research showed that these pass cards
are often called “proximity cards,” and operate in
a manner similar to the tiny RFID tags found inside
the new U.S. passports and even pet dogs. (See
“How Does It Work?” on the following page for
a basic explanation of their operation.)
Bending the card slightly to widen the crack
revealed a coil of fine copper wire inside, and when
I dismantled the card completely, I was surprised
to find that its plastic shell contained not only a coil
but also a small integrated circuit (IC) on a printed
circuit board (PCB). Even more surprisingly, it had
no battery!
I carefully removed some of the outside shell to
reveal more (Figure A, following page), and then
exposed the coil and PCB completely.
With the aid of a jeweler’s loupe, I could see that
the wire coil had broken —in many places, unfortunately. It would have been a major job just to
identify the correct wires to solder back together, let
alone actually doing it! Plan B was to wind my own
coil, but back in the depths of my mind were the
makings of Plan C: replacing the coil with one from
another card.
121 Make:
