A versatile easy to use XIAO RP2040 LoRa Fusion

In this post, we will look at a versatile easy-to-use XIAO RP2040 LoRa Fusion. The SEEED Studio Xiao RP2040 should, by now, no longer be a stranger to any of us makers and electronics enthusiasts. At its heart, it contains the same RP2040 processor that is used on the Raspberry Pi Pico.

What makes, the Xiao RP2040, special is its size, only 20.00mm x 17.5mm, as well as the carefully curated combination of GPIO pins, single-sided board construction and castellated pads to make incorporating it directly into a design an absolute pleasure.

Features

  • Powerful MCU: Dual-core ARM Cortex M0+ processor, flexible clock running up to 133 MHz
  • Rich on-chip resources: 264KB of SRAM, and 2MB of onboard Flash memory
  • Flexible compatibility: Support Micropython/Arduino/CircuitPython
  • Easy project operation: Breadboard-friendly & SMD design, no components on the back
  • Small size: As small as a thumb(20×17.5mm) for wearable devices and small projects.
  • Multiple interfaces: 11 digital pins, 4 analog pins, 11 PWM Pins,1 I2C interface, 1 UART interface, 1 SPI interface and 1 SWD Bonding pad interface.

Specifications

Value
Dual-core ARM Cortex M0+ processor up to 133MHz
2MB
264KB
11
4
11
1
1
1
Type-C
3.3V/5V DC
20×17.5×3.5mm

The AI-Thinker RA-02 also need no introduction from me, as I have used it extensively in quite a few projects before. With the worldwide chip shortage, building solutions around the easily available RP2040, and RA-02 makes perfect sense, as these two modules are also super cheap. For this project, I have also decided to try out a fully factory-assembled PCB to compare quality, as well as the convenience of being able to focus on software without doing assembly first, not that I mind assembling my own boards though… More on that experience later…

What were my intentions with this project?

I had the following goals/needs: 1. A modern, easily obtainable processor, that is not only cheap but also energy efficient. The RP2040, in the form of the Xiao RP2040, fits that goal perfectly. 2. An as-small-as-possible footprint for the main processor, without having to resort to manually designing a Pi Pico derivative – The RP2040 chip is a bit tiny for my eyes 3. The minimum of external supporting components to make the design function 4. Flexible power options ( 3v or 5v )

As to my use intentions, I use quite a few LoRa devices for various different purposes, so adding another option seemed like a good idea. In the current design, providing that the Arduino libraries stay compatible, the new design will support not only LoRa but also FSK and OOK, with all the advantages of those. By changing the position of only 3 jumpers, I can also use the PCB for a general-use RP2040 development platform, or another RP2040 project. Taking all of this into consideration, the device will thus be ideal for any remote sensor application, as well as using it on the bench-top for prototyping

What features are on the PCB?

  1. All of the Xiao RP2040’s pins and pads are broken out onto the PCB, including the SWD port.
  2. The Xiao also has a user LED, and a NeoPixel on-board, which can easily be used for signal indication.
  3. Level shifted 5v I2C port, in addition to the standard 3.3v I2C, because all of our sensors are not always 3.3v compatible, and using external level shifters is not always so convenient.
  4. Access to the RA-02’s GPIOs (DIO1-DIO5) is provided, but most people won’t need to worry about these.
  5. Jumpers to connect some of the Xiao RP2040 GPIO to the special use GPIO on the RA-02, for example, GPIO1 and GPIO2, sometimes used with some of the more specialised LoRa libraries.
  6. Provision or powering the device via a dc barrel connector, or screw-terminal, as well as via the 3v input pins (make sure your supply has a capability of more than 300mA)
  7. A power management chip to reset the Xiao RP2040 when the supply voltage falls below 3.0v – To prevent unstable operation and possible lock-up. ...
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