DIY Transit Card Mod: Access Control Upgrade

How to Modify Transit Cards?

If you want to enhance your access control card, you can dismantle it to extract the original ID core.

Measurements reveal that only coils with an outer diameter of 22MM can fit. Don't underestimate the 3MM difference; it's crucial. The sensing distance is only about 1.5CM, which won't suffice, as some machines may have difficulty sensing it. You can cut the original card into a small rectangle measuring 2.5X4CM. NFC recharge tests show no issues; the distance is over 2 centimeters, making it compatible with all card readers.

Locate the position under strong light, blow with a wind gun for two to three seconds, or use a lighter to heat it up. Then, quickly use tweezers to extract the core; the action must be swift, as the glue will cool rapidly. Steady, precise, and swift.

Preparation of the original card:

Prepare the access control card for modification, with its internal components removed.

That small black square is the chip.

Chip's front side:

The enamel-coated wire used is from a transformer, measured with a caliper to be 0.3MM. The same wire was used for a water drop transit card before, with an outer diameter of 25MM and 16 turns, yielding good results. It worked flawlessly across all devices after some time: buses, light rails, subways, and recharging machines.

The coil on the flashlight is the main component.

Wind it in like winding a watch spring. For easier handling, you can first apply a thin layer of double-sided tape inside the shell before winding. However, if the sensing distance is too short, at 1.5CM, you'll have to forgo the access control casing since a coil with a 25MM outer diameter is the cutoff point.

Final product:

Drill a 1.5MM hole and thread a 1MM cord through it. Cut two cards into 2.5X4CM pieces, sandwich the coil and chip in between, coat with white 704 silicone for easy disassembly in the future, compress with a clamp to solidify, then trim the edges.

Comparing it with the access control card casing, the 2.5X4CM size is indeed small and convenient to attach to keys or phones. Decorative tape and stickers are wrapped around the exterior.