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 there is a small U,FL connector where an LTE antenna should be connected. The antenna must have 50 ohm impedance and should be mounted according to the manufacturer’s specifications.

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 break 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, on this board the second UART is used for communicating with the LTE modem.
• 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).
• 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 onboard 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 SARA R410M.

The board uses the second UART (UART 1) of the MCU to connect to the LTE modem. In addition to the RXD and TXD signals the RTS and CTS signals are also connected to support large data transfers. Three more GPIO pins are connected to the power on and reset pin of the device.

• GPIO4 acts as UART1 TXD
• GPIO5 acts as UART1 RXD
• GPIO6 acts as UART1 CTS
• GPIO7 acts as UART1 RTS
• GPIO13 is connected the power on signal of the SARA R410M module.
• GPIO14 is connected to the reset signal of the SARA R410M module.
• GPIO15 is connected to the LDO that supplies the modem with power.

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