Challenger RP2040 NFC by Invector Labs

The Challenger RP2040 NFC is an Adafruit Feather format board based on the Raspberry Pi RP2040, with an NXP PN7150 NFC controller on board. Unlike a simple NFC tag, the PN7150 is a full reader/writer: it polls for NFC-A, NFC-B, NFC-F and NFC-V targets and speaks NCI over I2C, so CircuitPython can read and write NDEF messages on NTAG/Ultralight, MIFARE Classic, DESFire and ISO15693 tags.

It shares its layout with the rest of the Challenger RP2040 family (USB-C, 8 MByte of flash, a LiPo connector and charger, and a NeoPixel), so it drops into a Feather-shaped project like any other board in the series.

Using the NFC controller

The PN7150 sits on its own I2C bus, exposed as board.NFC_SDA and board.NFC_SCL, with board.NFC_IRQ and board.NFC_RESET for the interrupt and VEN lines. That bus is internal to the board and does not appear on the headers; board.I2C() is the separate header bus on GPIO0/GPIO1.

circuitpython-pn7150 is a single-file driver for the controller that imports nothing outside the core modules. It reads NTAG/Ultralight, Mifare Classic, DESFire/ISO-DEP, ISO15693 and FeliCa, decodes and writes NDEF, and can emulate a Type 4 tag so that tapping a phone on the board opens a URL. It recognises this board’s pin names, so PN7150.from_board(board) wires itself up:

import board
from pn7150 import PN7150

nfc = PN7150.from_board(board)
with nfc:
    for tag in nfc.scan():
        print(tag.type, tag.uid_hex)
        if tag.ndef:
            print("  ->", tag.ndef.value)

It is in the CircuitPython Community Bundle, so circup install pn7150 fetches it, or you can copy pn7150.mpy from the latest release into CIRCUITPY/lib/. ElectronicCats_CircuitPython_PN7150 is the other driver for this chip; it covers tag detection, and its example needs frequency lowered from 400000 to 100000 to run here.

The on-board bus has no external pull-up resistors, so this board is built with CIRCUITPY_I2C_ALLOW_INTERNAL_PULL_UP and busio.I2C enables the RP2040’s internal pull-ups on it. Those are weak, so construct the NFC bus at 100 kHz. 400 kHz will time out. Note also that i2c.scan() does not list the PN7150: it ignores the zero-length write that scan() uses and only answers real NCI frames.

Technical details

• Raspberry Pi RP2040 dual core Cortex-M0+ @ 133 MHz
• 264 KByte SRAM, 8 MByte flash
• NXP PN7150 NFC controller with integrated firmware, on a dedicated I2C bus
• Reader/writer for NFC-A, NFC-B, NFC-F and NFC-V targets
• 1 hardware I2C, 1 hardware SPI and 1 hardware UART on the headers
• 4 x 12-bit ADC inputs
• NeoPixel and a red user LED
• LiPo charger and standard LiPo battery connector
• USB-C connector

The board ships without an NFC antenna. iLabs sells it as a kit with one, or you can attach your own to the antenna pads.

Purchase

• Invector Labs

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