LoRa Expansion Card

I have designed a LoRa expansion card. You can find it here.

At this moment I haven’t made it yet, so no guarantees that it works. If anyone is interested and want to review it, feel free to do so. I think I’ll order parts in a few weeks.

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I’m really interested in this but for some reason the link doesn’t work for me. Maybe the project is private?

You are right. Should be public now.

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Looks very cool! I look forward to hearing about your build!

@S115 this is awesome. Have you looked into using an integrated matching/balun part? You can potentially simplify the layout a lot with something like 868/915MHz IPD for Semtech SX1261 & SX1262 LoRa - Johanson Technology

The other interesting option is to use an off the shelf module that is pre-certified. This one has an RP2040 built in to interface to USB: RAK11300 WisDuo LPWAN Module Datasheet | RAKwireless Documentation Center

There’s also stuff like this that is smaller but would need to be attached to an MCU: https://files.seeedstudio.com/products/317990687/res/LoRa-E5+module+datasheet_V1.0.pdf

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The Johanson filter is a great option. That will for sure be a better option than the “large” filter I have now. Thanks for the tip!

Unfortunately I haven’t found an off the shelf modules that will fit as a retro fit. The one you link for example is 3mm thick, which will already be too much.

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I am looking at the mechanical aspects of the expansion card but am struggling to fit the SMA connector nicely. At the moment I designed in Taoglas EMPCB.SMAFSTJ.B.HT but that sticks out 0,7 mm above the card.

The best solution I can come up with is to use this connector, but mount it floating centred to the PCB. Instead of how it is supposed to be SMD mounted. But mechanically that is not ideal.
My best solution
How it is supposed to be

Anyone know a better solution?

Interesting potential module that just launched today: Type 2GT(LBAA0XV2GT-001) | LPWA Products | Murata Manufacturing Co., Ltd.

I looked into RF connectors before, and remember MMCX seeming like the smallest that could fit within Expansion Card constraints.
Not necessarily this specific one, but
a mid-mount MMCX could work: 0734150969 Molex | Connectors, Interconnects | DigiKey

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That is a nice module indeed. I have requested a datasheet and price indication (as it is not publicly available yet). Let’s see what they say.

I think technically an SMA connector should just about be possible. But practically have not found one that fits. I think for a first version I’ll go with my less than optimal solution since most antennas use an SMA connector. For a final version MMCX might be the nicer solution.

I have also been working on a LORA expansion card. It is based on the Heltc HT-CT62. (https://heltec.org/project/ht-ct62/). My plan is to have two screw on connectors recessed into the side of the expansion card (much like a current pcie wifi card) as well as a small fractal antenna included inside the module (from another laptop probably) so the external antennas aren’t needed but can be used to increase signal integrity… waiting on the heltec module to ship and make the first version.

Which screw connectors are you planning on using? Maybe I can use those as well.

I was thinking just using SMV if I can find them, otherwise SMB vs SMA may fit a bit better. The rough plan was to have the antenna screw into a slightly recessed SMB (or V or whatever) male connector that is in the expansion card itself so the SM* connectors aren’t protruding from the card when the external antennas aren’t in use to minimize the chances of damage to the connecters. A SMA to SM* adapter can be used to connect any type of SMA female antenna like these: SMA to SM* (or similar)
Also I was thinking of making small silicone plugs similar to the ones sold on ebay for macs or other computers to plug usb ports and what not to keep dirt out of the connectors when not in use. The one nice thing about the Heltec module is it is pretty inexpensive (roughly 7$) and has ipex connectors on the chip itself which is a huge benefit as far as not having to try and find SMA surface mount connectors for a circuit board that fit inside an expansion card. The one thing I still am trying to figure out is how to connect a laptop fractal antenna like this: (space permitiing) laptop antenna and the SM* connectors to the same ipex connectors on the module. I am not very fluent in radio interference calculations so I don’t know what the most optimal setup would be…

The general plan is to have the Heltec module in the expansion card and have the D+ D- pair as well as power and ground to the USB-C port inherent to the expansion cards and hopefully the module will be able to use the USB data pairs to flash and use the Heltec module as a serial LORA modem basically. I still am unsure if SPI or another protocol is necessary on the module to be able to flash and use the HT-CT62 normally, the product datasheet is a bit unclear about that and I am a bit naive to how exactly the module integrates. I am going to just throw it into a 3d printed module case and see how it all fits and work from there, I’m sure as I iterate more problems with come up and be solved as I go…

this a great SMC to SMA connecter I just found, so maybe ipex 1 to SMC internally in the expansion card and then use the SMA to SMC connector to attach whatever SMA wifi antennas you want…

I’m no EM specialist either but I don’t think all the metal close to the expansion card will be very helpful for an PCB/chip antenna.

Anyway I designed in the Murata module and made a “render” of the assembled card. (Although I do not have actually have the datasheet of the module yet, they have publicly posted a version of the 2DT version. Which I think is the same, just with GNSS added.)


First rough fit is very promising… now to design the 5v to 3.3v step down and usb connection. Hopefully then i’ll be able to iterate on antenna designs as you have…


This is a rough learning curve, but I’m getting there… There is also plenty of room for a 2.4g pcb antenna on the bottom of the pcb… i wonder if it is worth adding it for when the larger antenna arent plugged in

Well, as long as you are on the learning curve your heading in the right direction :wink: I don´t know if you were done with your rough layout already. But a small suggestion on the voltage regulator. You generally want the capacitors close to the regulator. If you have trouble fitting the ones you have, you can use multiple smaller ones as well (as long as the values add up to the same total).

For the antenna I suggest you check the datasheet of the module. It will probably have a section on how the antennas are handled. It could be that you can switch, but it is also possible that there are different hardware versions of the module.

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Thanks for the heads up!