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  • Author Author: shabaz
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Adding Wireless Capability to Custom RP2040/RP2350 Projects: Pi Radio Module 2 - Anyone tried it?

shabaz

I just noticed the other day that this thing existed; it supports 2.4 GHz wireless (not 5 GHz), and Bluetooth LE (BLE); the manufacturer part code is RMC20452T , also known as RM2 and it costs about $4. 

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Underside; the board is 16.5 x 14.5 mm in size (but you'll need some space for a ground plane):

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The RM2 is useful for custom RP2040 or RP2350 projects where WLAN (again, annoyingly just 2.4 GHz)/BLE is needed; not useful for anything else as far as I'm aware. From a software perspective, coding should be no different to using a Pi Pico W.

The RM2 should be very easy to drop into KiCad projects, since the footprint/symbol/3D model is available.

The RM2 datasheet (PDF) seems easy enough to follow, but is extremely basic; and I found it a bit confusing regarding a 'reset' line it mentions, but the text is silent on that later. It is not clear what line that refers to.

There are no suggested layouts (there might be if you sign an NDA, I wasn't willing to do that), the PDF just states a good ground plane is needed, and shows the copper fill keepout area.

Note that there isn't a version with antenna connector, however, one workaround would be to place the module on a PCB (large enough to have a ground plane, or perhaps use parts of an enclosure for that) and run the interface wires a short distance to the microcontroller, if you needed the antenna positioned somewhere not feasible on the main circuit board. Personally, if it were me, I would try to use the module in that way, i.e. on a separate PCB with short wires, before integrating onto a larger PCB; I'd much rather have it separately and position it for the best signal.

Anyone see a use for this module? Or if anyone has seen it in use, any photos showing how it was deployed in the design would be great to see. 

At some point I'd like to experiment with creating a PCB for it (EDIT: I've now created one), but I was wondering if anyone else had given it a shot, or were planning to, or would like to!

Thanks for reading.

 

Example Circuit and PCB

Here's the circuit I used:

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50 x 23mm PCB render, all passives are 0603-sized, and the LED can be 0805:

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The Gerber files, and KiCad source files are downloadable here:

export_gerber_wlan_ble_rev1.zip

rm2_wlan_board.zip

  • Here's an attempt (the link to the KiCad files and Gerbers has been placed in the blog). The board size is 50 x 23 mm, which costs £6.67 for ten PCBs (I will populate these by hand, the parts are large and easy to solder), including tax/shipping. A combined board with this and CC1101 would be good, I might try that at some later point, since I can see use-cases for both together.

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  • in reply to shabaz

    Oh, I realized that there some FEM for the same device mentioned in the datasheet. That supports 20dbm

  • in reply to shabaz

    That wasn't too difficult.. I decided to extend the 10-pin GPIO header to become 14-pin, and insert in those four connections (shown in yellow):

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  • Using the schematic mentioned by  just four GPIO connections are needed to the RP2040, and I was curious roughly were the module could fit on a minimal RP2040 design (e.g. (+) Making a Custom RP2040 Project with KiCad, Part 1! - element14 Community ). The illustration here shows the four required connections in yellow, and approximately where the module could be placed so traces could be routed easily (I'm not planning to do this with the particular circuit I'm working on, but will consider it for future, or maybe place a SIL header there, for wiring up later.

    Aside from those four connections, GND and 3.3V is needed of course (The Pimoroni Pico 2 W uses a ferrite bead on the supply), and the module has three GPIO, one of which is used for an LED, and another is wired to a potential divider attached to the USB 5V supply, but seems unnecessary (I don't think the firmware does anything with that, it is just for developer use if they want to see if the USB supply is present, so I think that could be omitted if it simplifies PCB routing).

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  • in reply to shabaz

    haha, nice tiny little device, but the TX power is bit low it is 12dbm max. I have seen some modules with +20dbm and that will increase the comm. range for sure. Another thing that I would look is how to make P2P link secure and hackproof. That way I am good to go.