πŸ’¬ rayBeacon: nRF52 on-the-go Development Kit




  • Hero Member

    Nice work! I think yours may be the first to include a NFC antenna connector or use a Tag-Connect. And the nRF52833 too.

    Are you having it professionally fabricated, or are you able to do the reflow at home using just a stencil and solder paste? If the latter, how do you manage it? For instance, I doubt I could align the parts well enough doing it only by hand.

    Also, what does the MEMS silkscreen on your 3D rendering refer to? Are you planning to add a MEMS microphone, or is it some other kind of MEMS that it's referring to?

    Is the nRF52833 a simple drop-in upgrade, or did you have to do something extra to accomodate it over what's normal for an nRF52840?



  • Thanks!

    The board uses aQFN73 package which is kinda two-row BGP with 0.25 balls, so soldering it at home may be quite tricky indeed. I've ordered assembly πŸ™‚

    The aQFN73 is common package for both nRF52833 and nRF52840. In this particular board you may safely use either nRF52833 or nRF52840 of your choice (need 105ΒΊC and direction finding, or rather more memory and the CryptoCell unit?) The only other thing you have to do is ensure pi network uses correct components for the selected SoC (I'll update the BoM as we can tune it) - the PCB remains the same. Generally speaking, many features are just matter of your BoM. Just do custom assembly by dropping support for USB (C20), NFC (J1, C18, C21), IR LED (or replace it with usual LED), buttons, nRF DCDC, 32KHz crystal, and so on.

    On the other hand, if you need an extra stuff for your device (like a MEMS, or microphone, or air quality sensors), you may develop and attach an extension "slice" board. The "slice" supposed to be placed on the back side, i.e. right behind the CR2032 battery. Thus way it will create a kind of sandwich (or probably better said, burger): the Raybeacon board - battery - custom slice board. The red board on the screenshot is an example of such slice developed for my friend. It provides ultralow-power accelerometer, magnetometer, and gyroscope - all in all, we have just CR2032 for that.



  • By the way, for hand-soldering version I planning to employ nRF52833 in 5x5 QFN40 package when it will be available. It won't be possible to install anything but 833 there, but the PCB itself should be way more affordable to manufacture and assemble. I think the new board will be 100% compatible with existing "slices" . The current form factor depends on battery size in the first place, and I think it will remain the same. Unsure those 5mm will make big difference if we switch from 2032 to 1632 and loose about 50% of capacity.


  • Hero Member

    @mishka Just a thought, but since you have the skills to do antenna design, maybe you can leverage that by somehow retro-actively improving upon the designs of some inexpensive modules that lack good antennas. Right now the smaller the module, the worse the antenna, but maybe there's some way to improve on that after-the-fact with a design that's easily hand soldered, where, say, a pcb antena is soldered onto the module and the module's antenna (if any) is scrapped. It might perhaps be a similar approach to the HopeRF paradigm used for other radios.

    HolyIOT had some really tiny modules that @Nca78 and I tried out once (thinking back it may have been the nRF52832 though). They were very inexpensive, but the range was not at all good. Ironically, though, because of chinese economics, it may be cheaper to buy such a an already soldered and tested module with castellations and/or large bottom pads than it would be to buy even just the nRF chip by itself. Not sure how it plays out with 40 pins, though some of those would be entirely consumed on the module and shouldn't extend beyond, even if it were possible.

    Or, failing that, maybe there's some kind of bolt-on antenna that would nonetheless be a lot better than a cheap chip antenna: https://www.digikey.com/products/en/rf-if-and-rfid/rf-antennas/875?FV=1851|129348%2C1851|129459%2C1851|129922%2C-8|875&quantity=0&ColumnSort=0&page=3&k=pcb+antenna&pageSize=25&pkeyword=pcb+antenna I'm not sure about the 2.4ghz options, but a number of us did have a generally good experience with aftermarket 915Mhz antennas when attaching them to an RFM69 module. So, maybe there exists something as good or better that's meant for 2.4ghz. On the plus side, because of the shorter wavelength, it would probably be even smaller.

    e.g. maybe this? https://www.lairdconnect.com/rf-antennas/bluetooth-antennas/nano-ant-series-wifibluetooth-internal It's a mere 3x4x10mm in size.

    Any thoughts?



  • Hi @NeverDie, unfortunately, not much of the skills πŸ™‚

    Generally speaking, it's matter of choice between gain and size, that's right. Among all modules there are two options available: uFL connector (or other connector, or a hole) and a pre-mounted antenna (either PCB or ceramic). Although it should be virtually possible to replace a board-mounted antenna with any other solution, the new antenna will extremely likely require tuning, and this may kill the whole idea to replace it at home (until you have a vector network analyzer to tune it, of course). However, assuming very low cost of some Chinese modules it may worth to give them a try with a wire antenna. A raw conductor of half-wave length (or quarter-wave if you have too few space, plus some excess for tuning) may be a tricky yet simple solution. Connect it just right after the RF matching network (on my design the point is between L2 and C22) and scrape the rest of the layout. If unsure - scrape only the PCB antenna and solder the wire in its place through a drilled hole. Then tune it by measuring radio performance and cutting the wire a little until it will work best. Eventually you should end up with something like this: http://www.embien.com/blog/wp-content/uploads/Wire-and-Helix-Antenna-300x203.png

    A module with uFL-alike connector is much easier to extend. You may connect any of those antennas on the link above and they should provide acceptable performance out of the box. You may also create custom board with a high gain antenna (such as http://www.ti.com/lit/an/swra350/swra350.pdf) and put uFL on top of it, and then connect them via uFL-uFL 35mm cable. But the ugly thing is that the cable itself may cost more than $5, and you have to pay for balun and connector on the module. Anyway, it depends on application so connecting something like the SWRA350 or this one - https://martybugs.net/wireless/biquad/images/complete.jpg - may worth it.

    Finally, speaking about the nRF SoCs - by default they use 0dBm power for transmission (auto adjustable on connection though), so if connection from module to a central is weak it might be reasonable to bump it a little with +3dBm or +4dBm using sd_ble_gap_tx_power_set() call.



  • And getting back closer to the Nordic - they maintain a list of modules at https://www.nordicsemi.com/Software-and-tools/3rd-Party/3rd-party-modules. Many of them offer really good specs. For example: "Range between two BM833s is estimated at 1400 meters at 125 Kbps; between two BM833F is estimated at 2300 meters at 125 Kbps".


  • Hero Member

    @mishka Yes, if cost is no issue, the Fanstel BT840X and BT840XE have by far the best range out of all the modules I tested. I had hoped their price would come down by now, but, if anything, I think their price may have actually gone up instead. Presently, $24.82 on digikey for a BT840XE. For that reason, I was hoping: is there any chance it would be possible to match their performance with a inexpensive bolt-on to a cheap module?



  • @NeverDie do you really need it so far? From what I see the BT840XE uses active RF amplifier which boosts it up to +21dBm (BTW may be cumbersome to use it legally in open air). In any case, I'd look for either cheaper alternative, like this - https://www.aliexpress.com/item/32951920205.html. Or use high gain antenna, like this: https://www.gearbest.com/networking-communication/pp_257707.html


  • Hero Member

    OK, so maybe this makes the point better: at $3.48 (including delivery) for a complete nRF52840 module, such as: https://www.aliexpress.com/item/32944356249.html?spm=a2g0o.detail.1000014.25.6dbb36481kBpeJ&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.133222.0&scm_id=1007.13338.133222.0&scm-url=1007.13338.133222.0&pvid=b2b2c812-9dd8-457d-be28-379855aa8aff

    as compared to $6.38 for just the chip itself (plus delivery): https://www.digikey.com/product-detail/en/nordic-semiconductor-asa/NRF52840-QIAA-R/1490-1071-1-ND/7725416

    The main limitation of the above module is the limited range caused by the chip antenna.

    Do I really need better? Maybe. Maybe not. I'd never say no to extra discretionary link budget, especially if it can be had for very little extra cost.

    I don't mean to dissuade you though. By all means, proceed. I'm just wondering if there isn't a good arbitrage to be had, and I only ask because you apparently have the antenna skills to maybe (?) judge whether it's possible. Or maybe have ideas on how best to do it. Sorry for the vagueness of the question. If it resonates at all with you, then great. If not, I'll just leave it at that.


  • Hardware Contributor

    @neverdie said in πŸ’¬ Raybeacon: nRF52 on-the-go Development Kit:

    as compared to $6.38 for just the chip itself (plus delivery): https://www.digikey.com/product-detail/en/nordic-semiconductor-asa/NRF52840-QIAA-R/1490-1071-1-ND/7725416

    This is a bad example, you can get the chip at $2.824 at Arrow.
    You only need to buy 7,000,000 of them πŸ˜“



  • Well, looks like the CDEBYTE did great job by placing all required components. From the datasheet (yes, there is one, and that's awesome) I see the only missing part is 32.768kHz crystal which is not an issue either.

    The antenna is huge. If it was tuned properly it may give us up to +5dBi easily. Also, the 840 can be boosted up to +8dBm. IMHO this module looks like being serious about long range. I think you may get up to 1 km of it as is.

    Another good thing about the module is that it has easily accessible waveguide. Probably it may be possible to unmount the antenna, crop the board a little, and inject an RF front end (like SKY66405-11) to gain some +10dBm more. As I said, the antenna is good so it's worth to reuse it and save little bit more money. Tune it once and then call it a reference design. I don't know can someone make it to 5 km, but would be interesting to see the range.

    Anyhow, I've just spend $5 for my couple, thanks for the link! πŸ™‚

    Regarding the Raybeacon module - it was created as a tiny board for development on the go. I could take a Feather, but this one is smaller and has battery attached. Someone may also consider it as a reference design for own boards (as we in Raytrails do). Long range wasn't the goal here. I totally agree - employing a module is a good practice. Unfortunately, I just found no module with zero clearance for antenna so decided to go this way.



  • Hi,

    I'm very gald to post an update to the project. Revision 0.6 features fully round shape for the main board (and hence all extension boards). The battery placement is off-centric now, but it should fit just fine together with the extension socket. Please note, the dedicated ground pad has been also moved and now it's conveniently located right below the USB pads.



  • And here is the revision 0.7.

    It adds 2x4 1.27 pitch pin header on the front side of the breadboard part. The connector is fully matches the Raybeacon extension socket - you may safely break the breadboard part off, and then solder a pin header there in order to use the detached piece as 1.27 to 2.54 adapter.

    With this change, need for a dedicated dock board is perhaps even less. If so, flip the SWD socket bottom up.



  • @neverdie said in πŸ’¬ Raybeacon: nRF52 on-the-go Development Kit:

    I'd never say no to extra discretionary link budget, especially if it can be had for very little extra cost.

    By the way, the module should fit just fine into a can. Lowest price guarantee B-)

    Also, it should help avoid interference from bazillions of other sources.


  • Hero Member

    @mishka Makes sense, but in that scenario wouldn't it still need some kind of tuned antenna on the module itself to let the energy out of it during Tx?


  • Hero Member

    The F-type trace antenna on the esp8266 esp-12F seemed to be the best all-around solution, so I was previously guessing the same would probably be true for the nRF52 as well.

    alt text

    Then again, the Fanstel BT840X trace antenna seems to be by far the best so far, and it's bigger than the esp-12F antenna:
    alt text

    I'm guessing maybe part of the reason it does so well is because it has less insertion loss than an externally mounted antenna. So, to your earlier point, putting a BT840X inside a cantenna should easily beat externally mounting it to one.

    That said, my best experience to date has been with dipole antennas. They're larger still, but they're also very easy to make. Some people have even hacked them onto nRF24L01's and report much better range. I'm guessing that's at least partly because it compensates for the too small ground plane on those devices:

    alt text

    Luckily, at 2.4ghz the antennas wire length isn't as awkward as it is at sub-ghz. Maybe it could be shrunk down using two squiggle traces instead of just one?



  • @neverdie said in πŸ’¬ Raybeacon: nRF52 on-the-go Development Kit:

    The F-type trace antenna on the esp8266 esp-12F seemed to be the best all-around solution, so I was previously guessing the same would probably be true for the nRF52 as well.

    Well, antenna parameters are relevant only to resonant frequency. As long as it matches 2400-2485MHz it should work just fine.

    This one on the photo looks like SWRA117 by TI. I used those from KiCad standard library as a simple drop-in solution and they are quite nice.

    Then again, the Fanstel BT840X trace antenna seems to be by far the best so far, and it's bigger than the esp-12F antenna:

    Yeah, where reduced size is a must, meandered antennas (like the SWRA117 above) are good compromise to straight inverted F-type antennas. Otherwise a straight IFA might show slightly better efficiency.

    I'm guessing maybe part of the reason it does so well is because it has less insertion loss than an externally mounted antenna. So, to your earlier point, putting a BT840X inside a cantenna should easily beat externally mounting it to one.

    Placing antenna into a can makes to it about the same thing as acoustic guitar body to sound wave - it helps create standing wave and direct it into one particular direction. This simple trick promises to give +10..+15dBi - about the same gain as a power amplifier.

    The difference, of course, in radiation pattern. This actually defines the need: do we need long range connectivity in one direction, or it has to be rather omnidirectional? For the first case - use directional antenna, then shape the beam with a can (cheap) or parabolic reflector (affordable), if still low - amplify. Of course, size matters so a small and simple properly placed reflector would make it too. For the latter case just stick to omnidirectional antenna and amplify.

    That said, my best experience to date has been with dipole antennas. They're larger still, but they're also very easy to make. Some people have even hacked them onto nRF24L01's and report much better range. I'm guessing that's at least partly because it compensates for the too small ground plane on those devices:

    Bigger ground plane usually promises better performance indeed and the module looks very small.

    But to be honest, I don't know will the dipole improve anything or not. The nRF24 has balanced antenna feed line so at least it should be possible to connect dipole directly to the module (which is not the case with nRF5). But in order to do this all extra networks must be cut out, and even in this case it's very unlikely the antenna and RF output will match each other. Assuming that both the DIY dipole and the Cypress MIFA are omnidirectional antennas I don't think that the detuned and very likely out of band dipole would beat the original design, sorry.

    Luckily, at 2.4ghz the antennas wire length isn't as awkward as it is at sub-ghz. Maybe it could be shrunk down using two squiggle traces instead of just one?

    The RF output has 0dBm. Next, the default omnidirectional antenna tries to radiate it with 0dBi gain. Now it's possible either amplify, or shape the beam, or do both. A directional antenna (including reflector as part of it) could help gain up to +20dBi in front (which roughly means you'll have -10dBi in other directions). Amplifier could add +15dBm more in all directions. So it depends.

    IMHO the options (inclusive) are as follows:

    • Use reflector. Pros: high gain, cheap. Cons: size. Note: results in directed antenna (which may be both good and bad).
    • Replace antenna. Pros: better radiation pattern. Cons: needs tuning.
    • Install amplifier. Pros: immediate tx/rx gain boost. Cons: extra cost, needs tuning, may drain battery on low-powered solutions.


  • Hi,

    I'm pleased to announce that the first major release of the Raybeacon DK is out. The revision 1.0 offers all the mentioned features and can now be ordered from your favorite PCB service. For highlights please take a look to the OpenHardware description, for details (and sources) please visit the Raybeacon project page.

    I've published project BoM on the Octopart where you may easily estimate components. Please note, the aQFN73 package may push you to higher PCB production line. In particular, it suggests ENIG finish and also requires 5 mil track width / clearance, so expect increase in production costs. At the same time I've tried to keep design of the extension slices at the most affordable price so it should be easy to get 10 for $5 and have some DIY fun during Xmas holidays.

    The project still work in progress. Such, the radio was tuned for the nRF52840. The nRF52833 may work just fine or may be out of tune. I'm going to order several boards with 833 for that purpose, but it may take a while so please use 833 at your own risk.

    And, of course, please don't hesitate to share your feedback, it will be highly appreciated!



  • And in less than a week please meet the revision 1.1.

    This release addresses annoying NFC bug introduced in rev. 1.0. Such, to cleanup schematic I've moved NFC capacitors to a dedicated space where the C18 was turned upside down in order to improve text readability. This led to C18 net changes which were overlooked for the PCB. After zone refill it resulted in tying the GPIO_P0.10/NFC2 to the ground thus making the whole NFC antenna defunct.

    From the good, this revision adds highly requested mounting hole to the main board:

    Raytrails DK rev 1.1

    Have a nice time!



  • A little update. The nRF52833 test boards assembly was just finished. Now waiting for delivery.


  • Hardware Contributor

    @Mishka said in πŸ’¬ Raybeacon: nRF52 on-the-go Development Kit:

    A little update. The nRF52833 test boards assembly was just finished. Now waiting for delivery.

    Hello, who do you use to make the assembly ? Most PCB sellers who also do assembly have suspended the service at the moment.



  • Hi @Nca78, I've placed the order on the PCBWay in early January, so it's almost finished. The factory just recently restored assembly services for some kind of boards including this one. Hope to have it in hands within a week or two.



  • Assembly completed. Please see updated photos on the project page!



  • Hi guys, FYI the revision 1.2 just came out.

    After using the board for a while some non-critical fixes were introduced. To mention few:

    • The RGB LED got color and current optimizations. It's also recommended to stick to green or blue to minimize current consumption.
    • The breadboard adapter was inconvenient to cut-off and now fixed with a less fancy outline.
    • The board got AEC-Q200 qualified 32768Hz crystal.

    There are still some items on my TODO list (in particular, I'm not too happy about the extension socket - it can do more, and I'm going to address that separately), but the board is quite handy and definitely works. For this reason I think it's time to reset the W.I.P. bit and call the project stable.



  • The revision 1.3 is here! It adds hardware RESET feature to the SW2 push button, as well as to the SWD port. Not a big deal when attached to debugger, but so handy on the go.

    Please note, the change make break your firmware because SW2 was mapped to P1.02 GPIO and now linked to the P0.18 / RESET.



  • So, while here I've decided to close my TODO list. The revision 1.4 is likely to be the last chapter in this design, and now it can be considered safe to order. It introduces some important final touches to the board, in particular:

    • The orientation key (diameter 2.1mm) on the board edge. It's located between the Tag-Connect and the board main area, and initially can be used as an eyelet. After the Tag-Connect removal it works as an orientation key for the board.

    • Full rework of the silk layer. Just to mention few: I hid all designators and decorated the board with eye catchy "52" over the nRF52 MCU, touched the antenna outline, and moved the git hash to the mainland.

    • Review and cleanup the ground plane. The changes were tiny so it shouldn't detune the antenna, but aesthetics were definitely improved. You may also want to order the board in Afterdark colors now:

    raybeacon-afterdark.png

    Have fun!



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