Mehrdad Majzoobi's Raspberry Pi NFC Add-On Works Even When the Pi Is Powered Off
NXP chip gives this I2C NFC add-on board the ability to operate in both active and passive modes.
Maker Mehrdad Majzoobi has released another side-product of the Ubo Pod project: an open-hardware near-field communication (NFC) radio add-on for the Raspberry Pi family of single-board computers, with both active and passive operation modes — meaning it can work even when the Raspberry Pi is powered down.
"I recently designed an open-source HAT [Hardware Attached on Top] to bring NFC functionality to [the] Raspberry Pi," Majzoobi writes of his latest board, built as part of the ongoing Raspberry Pi-powered Ubo Pod project. "The design uses [the] NXP NT3H2211W0FT1 NFC Forum Type 2 tag with I2C interface. The cool thing about this chip is that it has power harvesting capability and works even if the Pi is not powered up."
NFC, a spin-off of radio frequency identification (RFID) technology that allows two-way communication between two devices, is designed for short-range tap-based communication — and most commonly found, these days, in retail terminals for both physical cards and smartphone payments. The technology has active and passive modes, with the latter used for cards: a large antenna captures energy from the reader and uses it to power an on-board system long enough to transmit a response.
The NXP NT3H2211W0FT1 at the heart of Majzoobi's board supports both modes of operation, which means that a Raspberry Pi equipped with what he is calling the Ubo NFC HAT can either participate in the NFC conversation itself or farm that off to the NXP chip — which will continue to operate in passive mode even when the host Raspberry Pi is powered off.
"In addition to the NFC chip, I decided to also include an addressable RGB LED ring (12 LEDs). The NFC chip has a Field Detect pin that you can monitor with your Raspberry Pi and show different patterns on the [status] LED (blink for detect or show progress wheel if data transfer is in progress, etc) to provide visual feedback," Majzoobi adds of the board's features. "The software side is quite straightforward as you can just read/write to given register addressed via [the] I2C bus to send/receive data (device goes on 0x55 address by default)."
A KiCad project for the board, which should be compatible with any model of Raspberry Pi accessible general-purpose input/output (GPIO) header, is available on GitHub under the same reciprocal GNU General Public License 3 as the rest of the Ubo Pod project; additional information is available in the maker's Reddit post.