Super NFC Bus Card

To be precise, this project is an NFC test board
 

used to detect and monitor whether NFC is working.

 

It can be used to drive LEDs.

 

Of course, it can also be used as a public transport card.

 

As an energy harvester (a key verification objective)

 
 
     , the product image is shown below (prototype and testing have been completed).
 
 
Note: This is an NFC card, not an active transmitter module; it can only be used as a receiver.
 
 
When using a passive card to detect NFC functionality, the bridge circuit U1 can be shorted in parallel. Removing capacitors and resistors and only soldering the LED allows for quick determination of whether the device is within the magnetic field coil's induction range by observing the LED's brightness. This is the most convenient approach. Many similar projects simply involve lighting a single LED to create various fun cartoon toys, such as a hand holding a red heart-shaped ice cream cone.
Of course, soldering resistors for current limiting and adjusting the LED's brightness is also a direct and feasible method. First, it's important to understand that a
 
public transport card
 
is simply a customer terminal card containing an identity ID. Only the ID registered in the terminal management system can be used for payment. Therefore, while some early public transport cards could be copied, it was essentially two users sharing one coin (similar to a parent-child card). Modern cards use a rolling code encryption design and cannot be copied. Even if copied, only one card can be used at a time; after one swipe, the other card is rendered unusable.
Therefore, a normal public transport card needs to be damaged. The chip inside is removed, and pins 3 and 4 of U1 are soldered on (neither positive nor negative). This allows it to be used as a new public transport card for top-ups and fares. It can also replace the coil.
 
Energy storage can be achieved using a complete circuit. The indicator light will light up when the NFC battery senses the magnetic field, typically around 2.5V. The duration of the light depends heavily on the amount of capacitor. Therefore, after the energy is extracted, the indicator light can remain lit for a considerable time; correspondingly, the longer the energy extraction time, the larger the amount of charge stored in the capacitor. I tried using the subway's electricity-stealing feature, and it was pretty good. It could be upgraded later, for example, with voice prompts to enable card swiping and subway entry. For instance, a voice prompt like "Everyone get out of the way, Miss is getting married!" This could be added in the next update. Please stay tuned!