This week on EYE ON NPI we're working without wires - it's the new RM2 module from Raspberry Pi (https://www.digikey.com/en/product-highlight/r/raspberry-pi/radio-module-2-wireless-connectivity) which will let you add 2.4GHz WiFi / Bluetooth LE and Bluetooth Classic over an SDIO interface at a great price.

The RM2 is built on the technology stack that Raspberry Pi has been working on for many years in adding built-in wireless to their microcomputers and microcontrollers. For example, starting with the Raspberry Pi 3 (https://www.digikey.com/short/59j9179b), the trading company has been integrating WiFi/Bluetooth to their single-board computers. With tight integration and onboard antenna, it's easy to bring up a new board with networking and native Linux kernel support. To do that, Pi has used the CYW43438 (https://www.digikey.com/short/8pfmdctc) and CYW43455 (https://www.digikey.com/short/99wr3vbq) which supports 2.4G and 5G.

When the RP2040 microcontroller chip (https://www.digikey.com/short/bnh55qj4) was released in 2021 along with the Pico board (https://www.digikey.com/short/0p02nwh2) - a year later they came out with the Pico W (https://www.digikey.com/short/bzjt9bcp) for only a few $ more. Instead of trying to design an all-in-one WiFi microcontroller, Pi decided to go the same route they did with the Pi SBC: have a co-processor that adds wireless and then offer the firmware support to make it easy for folks to make IoT projects with a powerful arm Cortex chip. Not surprisingly, the RP2350's Pico 2 also came out with a Pico 2 W (https://www.digikey.com/short/ph2b4dmn) variant pretty quickly. Both W boards have a tinned radio module at the end, reminiscent of the CYW chipsets on the Pi SBCs - in this case they feature the CYW43439 (https://www.digikey.com/short/2tj7twdc) which can do 2.4 GHz WiFi/BT/BLE but not 5GHz to keep the price low.

For folks who wanted to built upon the Pico W or 2W with their own design, integrating the CYW43439 (https://www.digikey.com/short/2tj7twdc) is non-trivial: it's a BGA chip which requires adding an antenna, managing traces and impedances as well as getting emitter certifications. So, it's not surprising that Pi trading has designed a standalone module that folks can solder into their designs to take advantage of the high-integration between the RP2 chipset and the CYW43439. The RM2 module (https://www.digikey.com/short/vp58vnh3) comes with antenna, tin and chunky castellated pads that can be pick-and-place'd or hand soldered. We've already seen this module used in some existing designs like the Pico Plus 2W from Pimoroni (https://www.digikey.com/short/rpjcp849).

Communication with the CYW43439 (https://www.digikey.com/short/2tj7twdc) inside the module is done over SPI plus some IRQ and reset lines. Note that while, in theory, you could connect this module to any microcontroller with a TCP/IP stack like lwip, it really is only designed and supported with RP2-series microcontrollers. That's because the Pico SDK (https://www.raspberrypi.com/documentation/pico-sdk/networking.html) which integrates the firmware uploading and WiFi stack is not really portable to other microcontrollers and there's a cyw32-driver (https://github.com/georgerobotics/cyw43-driver) that is not open source. We did notice that there's an 'open source' reverse-engineered driver on github (https://github.com/jbentham/picowi) - experimentation will be required for those interested! Bluetooth is more freely licensed via BTStack (https://github.com/bluekitchen/btstack)

If you want to add the new RM2 module from Raspberry Pi (https://www.digikey.com/en/product-highlight/r/raspberry-pi/radio-module-2-wireless-connectivity) to your next RP2xxx microcontroller design, for tried-and-tested wireless with lots of platform support, you can pick up some right now from DigiKey! Order today and your fresh modules will ship instantly so you can start integration by tomorrow afternoon.

https://www.digikey.com/short/vp58vnh3