Looking for "beginner" PCB for an Arduino Pro Mini paired with RFM95/96



  • Hi everybody,

    I'm new to this community and have spent the last two weeks setting up simple nodes with a couple of Arduino Pro Minis (3V3/8MHz) and basic sensors like DHT22, BME280. I'm aiming for easy to build/solder basic nodes running on a LiPo (for example an 18650 with a MCP1700) of 3x AAA NiMh; as fas as I gathered I should get at least a couple of months, perhaps a year runtime, but that's not my point here.

    What I wonder is are there simple PCBs for soldering an Pro Mini, but with an RFM95?
    Of course I found a lot of nicely designed boards like jmodule2/nmodule/EasyPCB, but those were all for NRF24 (which I have discarded for now as we have a lot so steel inforced concrete walls in our house and because I'm planning to additionally tap into TheThingsNetwork later) of the older, seemingly pin incompatible RF69HW.

    Perhaps anyone has seen a simple PCB I could order to tidy up things before deploying my nodes (in fact I'm planning to also bury some in the garden with capacitative soil moisture sensors)?

    Thanks in advance and also for the fabulous MySensors Library,

    Joost


  • Mod



  • @joost I wouldn't get too hung up on Lora to begin with or indeed the high power RFM69, the standard 433MHz modules have remarkable penetration of RC structures, much depends on aesthetics such as whether a110mm antenna is acceptable domestically.
    Second @mfalkvidd 's recommendation of the easyPCB by Sundbergh https://www.openhardware.io/view/389/EasyNewbie-PCB-RFM69-HWW-edition-for-MySensors as it is well thought through, and is widely known so help is always a keyboard away for all those WTF moments...
    Easy enough to build a pair using standard RFMs to test comms at the worst expected locations, you then re-assign for other Nodes if you require the HW in a set location and can incorporate to accomodate the "problem".



  • Hi guys,

    thanks very much for your rapid responses!
    I have a few explanations, also I am perhaps mistaken on some points.

    • I'm located in germany, that's why I got me 10 RFM96 868MHz transceivers already, assuming I have to get 868MHz and not 433MHz (?) due to regulations. I'm not especially after LoRa, just thought it would be low hanging fruit as I am already using compatible transceivers.
    • I browsed openhardware.io and had already seen the excellent Easy/Newbie PCB, wich looks 110% like what I'm after. I was so happy already, and then delved into the details... Here it says:
      "This is the RFM69(HW/W) edition"

    As I do not have an RFM69 to compare directly, I looked online for hints regarding pin compatibility to RFM95/96 and found the also splendid moteino site, especially this excellent picture:
    https://lowpowerlab.com/wp-content/uploads/2016/09/LowPowerLab_transceivers-1.png

    This made me believe that it is designed for the leftmost pictured RFM69H/HW, which looks incompatible to the transceivers I have (second column from the right, RFM95/96).

    Am I mistaken here?



  • Ah, the plot thickens, I have bought a batch of engines, can anybody recommend a car they may fit 😂
    The C series are smaller than the standards as is the Lora, I have a few C series RFM69s bought it "error", so can verify they are completely different.
    I recall coming across adapter boards which may offer some flexibility, but that rather depends on whether you are up to soldering your own boards or want to go the pre-built Moteino route...



  • Hi, I'm not sure I completely follow with the car analogy...
    Nevertheless, I started with RFM95 as that was/still is what my local shop here has available. Been trying to avoid ordering stuff in single digit quantities from the other side of the world, though I'll probably not be able to do so indefinitely.

    Looking at the picture with the different transceivers again, it seems as if the RFM C-Versions just are a bit shorter than the standard/non-C models, but have the same widths. This initially gave me hope that I might be able to use the EasyPCB with my radios by soldering just one row of pads and add some kind of short wire bridges to the other row of pads (which, by the looks of it, won't reach the pads), but I found in the RFM69 datasheets that they are pin incompatible between standard and C- models 😞

    So it seems to me right now there are no available options right now. Time to learn KiCad I guess 🙂

    But to get something done before Christmas I wonder if I switch to RFM69(H). Are these modules still preferred/advised (I mean as they seem superseded by the C- version, but this is just a feeling of mine), or are there downsides which the C- revision overcomes?

    Thanks for any insights,

    Joost



  • @joost "not sure I completely follow with the car analogy" - You bought the radios before identifying what it would be paired with, just my attempt at humour.

    From memory the Standard RFM69 versions are pin compatible, viz W and HW, but the CW and the HCW are not. Had to physically check, and you are correct that the C is shorter physically than the standard but the same width.
    I may be wrong here but from a cursory glance the RFM69W pads were labelled the same as RFM96_Lora... Perhaps you might verify that as your idea of extending wires (at the opposite end to the antenna only) may well be an option (You had checked compatibility only for the C variants, not between standard and the Lora).
    If not perhaps an adapter board is available, either way that brings the easyPCB back into contention.
    Perhaps @sundberg84 has observations on this since it is his creation.
    EDIT - Wrong on rechecking pad labels.



  • @Joost For the price, this could be a simple way to start
    https://www.electrodragon.com/product/atmega328p-arduino-plus-lora-sx1278-board-loraduino/, though it's not exactly what you're asking for.



  • @zboblamont
    Hi, thanks for confirming.
    I will probably look into KiCAD this weekend or the next week to see if I can import/adapt the nrf2rfm69 https://github.com/tbowmo/nrf2rfm69 board to accomodate an RFM69*CW size and pinout (which would be the same as RFM95/96), which would pave the way to all kinds of NRF24 based PCBs as far as I see. On the above GitHub seem to be KiCAD files already, I hope the learning curve won't be too steep.

    @ncollins
    Thanks for this new suggestion, looks pretty good!
    Will check the pinouts of SX1278 to see if it's compatible to SX1276 (it probably is, but it's too late right now :-), so my option would be to get the barebones ATMEGA328 board and fill in the RFM96 transceiver. Will dive in a bit more in the coming days; they have a link about low power usage which states some problems in the beginning, but it seems some folks have overcome them already, so this might pretty well be worth a shot. Thanks again!



  • @joost Although an adapter plate for your RFM96 would be by far the most compact arrangement for such as the easyPCB, there are other devices such as the Moteino built specifically for that series of devices, which can be ordered minus the transceiver. Not cheap though.

    @ncollins highlighted a remarkably cheap option, and doubtless there are others in the market since I Iast looked at what was available.



  • @joost I bought a few of these https://diycon.nl/product/lora-node-pcb-203-interface-pro-mini-rfm92-95, work fine, you can put a DHT22 on it too



  • @sweetpants Wow, that's just ...🙄 ... exactly what I am looking for! Thanks for the link!

    This gives me a pretty sweet-sour feeling though... In the last days I invested quite some time to get into some basic PCB designing with KiCAD and hacked something together as a starting point, and just now you link to the perfect solution for me 😝 😳

    I will upload the raw guts of my attempts here, perhaps I will continue with it nevertheless. In the last decades I never needed PCB designing skills, but perhaps with all this sensors stuff it might still be worth for me following along with KiCAD.



  • @joost The advantage of the version @Sweetpants posted is having solder pads for an antenna coupler...
    Glad you found a solution though...



  • Yeah, that's true. For now the copper coil antennas have been doing well for me, though I am curious what happens when I start to move the sensors out of the house and begin burying them with capacitative soil humidity sensors attached.
    Right now am starting to feel more comfortable already with KiCAD (v0.2 already has a BME280 footprint included), might include the antenna coupler pads as well.
    I read somewhere that the traces to the antenna pads should not be too long; would crossing the trace RFM module underneath count as "too long" as well? Then I would need to rotate the module, no big deal though.



  • @joost RF circuits are not simple, but a good rule of thumb is that the antenna should be free to radiate without obstruction. Coils are ok in free space, electrically the same as a whip, but I'll stick with the latter thank-you. At these frequencies a 1/4 wave is already pretty short...
    I would not recommend burying an antenna, but by all means try for yourself 😉



  • @sweetpants 👍 Thanks for the positive feedback.


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