The Challenger RP2040 NFC is a small embedded computer, equipped with an advanced on-board NFC controller (NXP PN7150), in the popular Adafruit Feather form factor. It is based on an RP2040 micro controller chip from the Raspberry Pi foundation which is a dual core Cortex M0 that can run on a clock up to 133MHz.

For more information about the RP2040 you can look here.

The RP2040 is paired with an 8MByte high speed flash capable of supplying data up to the max speed. The flash memory can be used both to store instructions for the micro controller as well as data in a file system and having a file system available makes it easy to store data in a structured and easy to program approach.

The device can be powered from a Lithium Polymer battery connected through a standard 2.0mm connector on the side of the board. An internal battery charging circuit allows you to charge your battery safely and quickly.

The NFC section on this board is based on the NXP device PN7150 which is a one-chip solution for implementing a NFC system on a very limited space.

The PN7150 is connected to the micro controller using an I2C channel (Wire1) and a 2 GPIO signals to handle interrupts and reset to the PN7150. The NFC antenna (coil) is hooked up to a FFC connector on the rear end of the board.

Short introduction to the board

PCB
The board is based on a popular form factor called “Feather” which is created and maintained by an American company called Adafruit. The entire specification for the Feather format is available here. The size of the PCB for the module is 50.80mm x 22.86mm but the entire module is a little bit bigger as the Type C USB connector protrudes about 1 mm outside the board.

Antenna
On the opposite end from the USB connector the you will find the NFC antenna connector. This is a 1mm pitch FFC connector that works very well within the frequency band of NFC. When mounting the antenna into or onto any enclosure you should make sure to keep stuff like cables and/or walls from the enclosure away from the antenna as much as possible. Anything mounted in the vicinity of the antenna will affect its performance.

Headers
On each of the longer sides of the PCB there are holes intended for soldering pin header connectors. If you don’t want to use connectors for some reason you can also solder a wire directly into the hole, making a permanent connection to your external device. If you go this way please make sure that the wires are fixed in place, otherwise vibrations can cause the wire to brake at the soldering point.

LED’s
On each side of the USB connector there is a small indicator LED placed. The LED which is marked CHG is the charge control indicator. This red LED will shine whenever the connected battery is being charged, and when the battery is fully charged the LED will turn off again. If you haven’t connected a battery to the board this LED will not come on at all.

On the other side of the USB connector there is a user programmable green LED. This LED is connected to pin D15 and can easily be controlled by the user program.

Hardware details

Pins

The on board micro controller (RP2040) have a number of communication channels that have been routed out to the side (header connector) connectors.

• UART – One UART channel have been routed to the header pins (RX, TX). The micro controller have 2 UARTs but on this board only the first UART is used.
• SPI – One SPI channel have been routed to the header pins (SCK, SDO, SDI).
• I2C – One I2C channel have been routed to the header pins (SCL, SDA) and the second channel is routed to the PN7150 NFC controller
• Analog pins – The micro controller have 4 analog input pins that all are available on the header pins (A0-A3).
• PWM – All pins can be used for PWM.

The pin chart below shows the placement of all pins and their respective functions. When working in an Arduino environment (or Platform IO) use the blue pins when writing your code and when working with CircuitPython use the orange marked pin assignments.

Power

The board can be powered from multiple sources. The most obvious way to run the board is by plugging it in to a USB cable and attach it to your computer. In this mode you can write software and test the board with all its functionality.

There is also a third way to supply the board. This way is more invasive and will disable the onboard 3.3V power regulator.

You will have to pull the EN header pin low and then supply your own 3.3V voltage on the 3.3V header pin. Please note that when disabling the onboard power regulator you will have to supply the 3.3V also when running the system on battery power.

Battery

As described earlier the board can be powered from a LiPo battery. The battery can be connected using a standard 2.0mm JST connector through the battery connector on the right side of the board or ff the battery is an integral part of the system that you are designing it is possible to connect the battery through the BAT pin instead.

Switching between the battery voltage and the applied USB voltage or external 5V is done seamlessly by the on board circuitry.

Charging of the battery is done by either connecting a USB cable or by connecting a 5V power source to the header pin marked USB on the board. If you do this make sure you connect your voltage through a 1A schottky diode to avoid any excessive current draw in the system when the two levels are slightly different.

Please note that providing external charger circuitry could destroy the internal charger on the Challenger board.

Connection between MCU and the PN7150 NFC controller.

The board uses the second I2C channel (Wire1) of the MCU to connect to the PN7150 device as well as a two GPIO pins to communicate with the module. The pins used are as follows.

• GPIO10 (SDA), GPIO11 (SCL) is configured as an I2C bus 1 (Wire1).
• GPIO9 (Arduino name PIN_PN7150_IRQ_B) is connected to the interrupt signal from the PN7150.
• GPIO12 (Arduino name PIN_PN7150_RST_B) is connected to the reset signal of the PN7150.

Antenna

We have also developed an antenna that is optimized for use with this board. You can check out more information about this antenna here.

Bi2C

Like most of our other boards this board also comes with the tiny I2C expansion connector. This system allows you to add I2C expansion units from both our own Bi2C system collection but with an adapter you can also add Stemma and Qwiic units. Read more about this innovative system here.

Documentation

• Schematic