Bus and metro cards, also known as contactless smart cards, use RFID (Radio Frequency Identification) or NFC (Near Field Communication) technology to communicate with the card readers at the gates or turnstiles. When you tap your card on the reader, the card and the reader exchange information wirelessly.
Here's a general overview of how the process works:
1. Card initialization: When you purchase and load a balance onto a bus or metro card, the card issuer writes the balance and other relevant information, such as an ID number or an expiration date, to the card's memory. This information is stored in an integrated circuit embedded within the card.
2. Card-reader communication: When you approach a gate or turnstile and tap your card on the reader, the RFID or NFC antenna in the reader creates an electromagnetic field. This field powers the card's chip, which in turn sends the stored information back to the reader.
3. Balance verification: The card reader checks the balance information received from the card and compares it against the fare required to enter the transit system. If the balance is sufficient, the reader sends a signal to the gate or turnstile to open or unlock, allowing you to pass through. Simultaneously, the reader updates the card's balance by deducting the fare.
4. Backend processing: The card reader communicates with a centralized database or server, synchronizing the transaction and updating your card's balance information in the system. This allows the card issuer and transit authorities to track usage and maintain accurate records.
It's worth noting that there are different types of bus and metro cards with various implementations, such as disposable paper cards, reloadable plastic cards, or mobile wallet-based cards. The exact process and technology may differ depending on the specific transit system and card issuer. However, the general concept of wireless communication and balance verification remains the same.
RFID & NFC
RFID (Radio Frequency Identification) and NFC (Near Field Communication) are related technologies, but they are not the same. Both RFID and NFC use radio frequencies for wireless communication between devices, but they have different purposes, ranges, and frequencies.
Here's a comparison of RFID and NFC:
1. Purpose: RFID is primarily used for identification and tracking purposes, such as inventory management, access control, and asset tracking. NFC, on the other hand, was specifically developed for secure, short-range communication between devices, enabling contactless payments, data exchange, and device pairing.
2. Range: RFID can operate at various ranges, from a few centimeters to several meters, depending on the type of RFID system (low-frequency, high-frequency, or ultra-high frequency). NFC operates at a much shorter range, typically up to 10 centimeters (~4 inches), making it more suitable for secure, close-proximity interactions.
3. Frequency: RFID operates at different frequencies, including low frequency (125 kHz - 134 kHz), high frequency (13.56 MHz), and ultra-high frequency (860 MHz - 960 MHz). NFC is a subset of high-frequency RFID and operates at a single frequency of 13.56 MHz.
4. Communication: RFID communication is typically one-way, with a passive RFID tag responding to a signal from an active RFID reader. NFC, however, allows for two-way communication between devices, enabling more complex and interactive data exchange.
5. Security: NFC has built-in support for secure communication and encryption, making it suitable for applications like contactless payments and secure access control. RFID, in general, does not have the same level of built-in security, though additional security measures can be implemented.
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