Introduction

The RP2040 Connectivity Board is a comprehensive IoT solution designed for modern applications. This board combines the capabilities of LTE, WiFi, and BLE into a single platform, making it ideal for a wide array of IoT projects. Based on the Raspberry Pico chip and compatible with the Arduino/PlatformIO, this board is perfect for both professional and hobbyist users who need multifaceted connectivity in their projects.

Key Features of the RP2040 Connectivity board are:

• High-Performance Microcontroller: Powered by the RP2040 from Raspberry Pi, featuring a dual-core Cortex M0 processor at 133MHz, equipped with 8 MByte of FLASH memory and 264 Kbyte of integrated RAM.
• Diverse Connectivity Options:
  • LTE (Cat M1/NB-IoT/eGPRS): Includes the SARA-R412M module for international GSM and LTE-M/NB-IoT coverage, offering robust IoT security and efficient data transfer.
  • WiFi/BLE: Integrated with the ESP32-C3FN4 chip, providing a full range of WiFi and BLE functionalities, including various operating modes and advanced features.
  • USB Type C Interface: Equipped with a modern USB Type C port, ensuring compatibility with contemporary devices and enhanced durability.
  • BConnect interface connector.
• Built in LiPO battery charger and standardized battery connector

Enhanced Power Efficiency:

• Low power supply design, enabling lower battery voltage operation and extended battery life.
• On board battery charger that charges the attached battery with up to 500mA, enabling rapid charging times.

User Interface and Programming:

• Two accessible buttons for easy reset and UF2 mode activation.
• Flexible antenna design with options for on-board chip antenna or U.FL connector for external antenna use.

Additional Specifications:

• Backward Compatibility: Ensures seamless software integration with previous board versions.
• Nano SIM Card Slot: Supports various prepaid SIM card options, including 1NCE IoT Flat Rate for LTE connectivity.
• Versatile Application Potential: Ideal for remote monitoring systems, smart connected devices, and other IoT applications.
• BConnect interface that allows the user to hook up a wide range of peripherals such as NFC readers, accelerometers etc.

The microcontroller

Again we have used the popular RP2040 from the Raspberry Pi Pico. An extremely well suited embedded processor for doing cool projects and managing high end communication devices such as the embedded modem. With its dual core Cortex M0 at 133MHz, 8 MByte of FLASH and 264 Kbyte of integrated RAM it will take a very long time before you run out of resources.

LTE (Cat M1/NB-IoT)/eGPRS

The module we selected to handle the cellular communication is the SARA-R412M series module. This module can be software multi-band configured, enabling international multi-regional coverage in both GSM as well as LTE-M/NB-IoT/eGPRS radio access technologies.

The SARA-R412M module is ideal for mission critical IoT solutions, as it includes a unique and immutable root of trust. It supports IoT security as a service and provides the foundation for a trusted set of advanced security functionalities. The scalable, pre-shared key management system offers data encryption and decryption, both on-device as well as from device to cloud. Utilizing the latest (D)TLS stack and cipher suites with hardware based crypto acceleration provides robust, efficient and protected communication.

Communication with the modem device is done over one of the hardware serial ports of the RP2040 and the board is configured for hardware flow control which allows you to use high data transfer speeds to and from the modem.

The supplied cellular antenna is connected to the board through a U.FL connector at the rear of the board. The antenna can then be attached to a plastic enclosure by peeling of the protective film and pressing it in place.

SIM Card

The board needs a nano SIM card in order to be able to connect to an LTE network and transfer data. Here you can either get it yourself or use our prepaid cards from 1NCE. The IoT pricing of the 1NCE IoT Flat Rate contains 120 months of connectivity services for 150 SEK. It is a one-time-payment only with no hidden costs. 1NCE offers one IoT data plan where all necessary features are included:

• 500 MB data volume with speeds up to 1Mbit/s
• 250 SMS
• SIM card
• Global coverage in 130+ countries (Check if your country is covered here)
• All mobile standards (2G, 3G, 4G, LTE-M, NB-IoT)

The SIM card that we supply is for evaluation only, If you want to take advantage of 1NCE full flexibility with their top-up option and their API’s you should get in touch with them directly here.

WiFi/BLE

The RP2040 Connectivity board is equipped with a powerful combined single chip solution that provides the WiFi and BLE connectivity of this board. The chip we are using is the ESP32-C3FN4 from Espressif and it is a complete WiFi subsystem that complies with IEEE 802.11b/g/n protocol and supports Station mode, SoftAP mode, SoftAP + Station mode, and promiscuous mode. It also implements A Bluetooth LE subsystem that supports features of Bluetooth 5 and Bluetooth mesh.

This solution is based on an RISC-V micro controller core and comes with 4MByte of internal flash and 408Kbyte of internal SRAM as well as the advanced 2.4GHz radio.

The ESP32-C3 device comes pre loaded with the ESP-AT interpreter already programmed into flash. This interpreter provides the system with everything from low level TCP/UDP functionality up to high level functions such as a on board integrated web server, MQTT server and client functions and much more.

From the get go the on board ESP32 delivers the following functionalities:

• Basic AT Commands
• Wi-Fi AT Commands
• TCP-IP AT Commands
• Bluetooth® Low Energy AT Commands
• MQTT AT Commands
• HTTP AT Commands
• Web server AT Commands

Setting an MQTT client up for instance is a matter of three lines of code, couldn’t be easier to use.

Antenna solutions

The board is equipped with a on board chip antenna for the WiFi/BLE radio and for the GSM/LTE part we have included a U.FL. connector that allows the user to hook up the antenna of their choice. We’ve also included a antenna detection circuit on the board which together with the appropriate antenna can detect whether an antenna is attached or not (requires special circuitry on the antenna).

External IO

We have equipped the board with a 26 pin expansion header that allow the board to connect a multitude of sensors, buttons, displays… well basically anything you need. Here’s a list of the connector pins and their functions.

Function	Pin	Pin	Function
GND	1	2	D2
D1	3	4	D3
D0	5	6	D18
SDI	7	8	D11
SS	9	10	D10
SCK	11	12	D9
SDO	13	14	D8
GND	15	16	GND
A3	17	18	3.3V
A2	19	20	VUSB (+5V)
A1	21	22	VBAT
A0	23	24	RESET (Active low)
AREF	25	26	EN (Pull low to deactivate module)

Buttons

There are two buttons on the board. The button closest to the battery connector is the reset button. Use it whenever you need to reset the unit. It has exactly the same functionality as the RESET pin. Then there is the BOOT button just next to the reset button. This button must be used in conjunction with the reset button to reset the RP2040 into UF2 mode. Press the BOOT button, then the RESET button for a short moment. Then release the RESET button (while still pressing the BOOT button) and shortly after that release the BOOT button. This will place the board in UF2 mode and show up in the computer as a mass storage device.

USB Type C

In the recent years we have noticed that we are seeing more and more USB Type C cable laying around the lab due to the fact that all new phones and accessories use them. As of yet we haven’t seen any shortage of micro USB cables but we are not getting any new ones any more and old ones do break occasionally. So we decided to go for a USB Type C connector for this board. A bonus of this is that they are quite bit more durable and you don’t have to fiddle with the cable before plugging it in.

Product Summary

The “RP2040 Connectivity Board” is a testament to the convergence of technology and innovation in the IoT space. Offering unmatched processing power and a suite of connectivity options, this board is your go-to solution for IoT projects demanding versatility, reliability, and ease of use. Elevate your IoT projects to new heights with the RP2040 Connectivity Board – your all-in-one solution for modern IoT challenges.

Pin chart

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.

GPIO connections between MCU and SARA module.

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 (D4) acts as UART1 TXD
• GPIO5 (D5) acts as UART1 RXD
• GPIO6 (D6) acts as UART1 CTS
• GPIO7 (D7) acts as UART1 RTS
• GPIO12 (D12) is connected the DTR signal of the SARA module.
• GPIO13 (D13) is connected the power on signal of the SARA module.
• GPIO14 (D14) is connected to the reset signal of the SARA module.
• GPIO15 (D15) is connected to the power supply circuit that supplies the SARA module with power.

GPIO connections between MCU and ESP32 device.

The board uses UART0 to communicate with the on board ESP32 device. In addition to the RXD and TXD signals there is also a reset signal and a boot select signal that is connected to support flashing of the device on board.

• GPIO16 (D16) acts as TXD of the RP2040 and is connected to the RXD input of the ESP32.
• GPIO17 (D17) acts as RXD of the RP2040 and is connected to the TXD output of the ESP32.
• GPIO24 (D24) is connected to the reset input of the ESP32.
• GPIO25 (D25) is connected to the boot select pin of the ESP32. Holding this pin low while releasing the reset pin will cause the ESP32 to enter programing mode.

Other internal GPIO pin usage.

• GPIO19 (D19/LED_BUILTIN) is connected to the user LED. Setting this pin high will light the on board green LED up.

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Documents:

• Schematic