💬 rayBeacon: nRF52 on-the-go Development Kit

[NeverDie]

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.

[Nca78]

@neverdie said in 💬 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 :sweat:

[Mishka]

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! :-)

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.

[Mishka]

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.

[Mishka]

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.

[Mishka]

@neverdie said in 💬 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.

[NeverDie]

@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?

[NeverDie]

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.

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:

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:

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?

[Mishka]

@neverdie said in 💬 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.

[Mishka]

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!

[Mishka]

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:

Have a nice time!

[Mishka]

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

[Nca78]

@Mishka said in 💬 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.

[Mishka]

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.

[Mishka]

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

[Mishka]

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.

[Mishka]

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.

[Mishka]

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:

Have fun!

[NeverDie]

@Mishka Very nice work indeed. One question though: I don't see an antenna of any kind built into the PCB. Maybe I'm just not seeing it, or is there none? I do see a connection for an off-board near field antenna, but off-hand I don't see where the antenna is for 2.4Ghz RF.

Oh, I see it now. You're using a chip antenna. Got it.

Well, now that you've been using it for a while, how is the Raybeacon working out for you?