BT antenna questions.

[enaon]

As some may know, I have been using espruino on many watches, as a dash for electric unicycles (EUC).

My main problem is that in all of the watches I tried, BT signal was bad. I get that most watches are good enough for watch to phone connection, but watch to EUC is a different scenario, connections have to be strong to withstand motor noise, urban city noise etc.

I have tried the DSD6, the DK8, the P8, the P22, the magic3 the rock and the bangle.js 2.

The P22 is the best one out of the box, but still not good enough to be flawless.

But I find it strange, that using a different length on the monopole makes a huge difference, the modified p8's I have are better than my phone, the same goes for the modded rock and dsd6's, they are flawless.

I think this is due to the manufacturers using "proper" monopole lengths (~26mm length), but plastic alters the behavior, they should not be standard length if enclosed in a plastic container. But I am not sure, so I opended this thread to have a talk if anyone cares.

I now have some years of experience, I know for sure that modified watches work reliable for years, I cannot see why they still use 26mm length. Any thoughts?

[fanoush]

I think this is due to the manufacturers using "proper" monopole lengths (~26mm length), but plastic alters the behavior, they should not be standard length if enclosed in a plastic container.

So what length do you actually use? Is it same for all watches or does each need different length possibly based on PCB design?
When googling I see suggestions like 28 to 32 mm, 31 mm etc.

[enaon]

So what length do you actually use?

I am not sure what the correct length should be, I was using trial and error, cutting a mm closing the watch placing it in my wrist and testing, and not every watch works best with the same length, this is why I guess the casing is important. I opened this thread because the button broke on my original P8, the one you gave me, I fixed it and I was looking at the antenna mod I had done back then. This one is 5.1cm but not monopole style, I have it like half cycle inside the watch, and for some reason it is excellent.

For comparison, the bangle.js 2 cannot keep the connection to the EUC if I raise my hand at eye level, but this p8 can connect to a unicycle 5 meters away, in urban environment, different level.

When googling I see suggestions like 28 to 32 mm, 31 mm etc.

yes this is about 1/4 of the wave length on the 2.4 spectrum (12.5cm), it is common, in practice it should be a bit shorter, this is why most watches use 2.6cm I think. The magic3 the rock and the p8 are 26mm, cut by hand, so 26-29 mostly from what I have seen. The 51mm I have used makes no sense, but works excellent, I find it strange. The most strange thing is that length 51mm is worse than 26mm if the back plastic cap is not in place, but becomes a lot better when I close the watch.

on the magic3 the best length is 39mm, I just measured it, again it makes no sense.

[gfwilliams]

For comparison, the bangle.js 2 cannot keep the connection to the EUC if I raise my hand at eye level

That's extremely strange - what RSSI do you see when connecting it to a phone? With BLE long range I've seen two Bangle.js 2 communicate over 100s of metres, so it seems crazy you're having issues so close.

I wonder whether it could be to do with polling interval? If the Bangle is connected to your phone at high speed (7.5ms) maybe there's not enough free time between packets to properly service the EUC?

[enaon]

For comparison, the bangle.js 2 cannot keep the connection to the EUC if I raise my hand at eye level

That's extremely strange - what RSSI do you see when connecting it to a phone? With BLE long range I've seen two Bangle.js 2 communicate over 100s of metres, so it seems crazy you're having issues so close.

I wonder whether it could be to do with polling interval? If the Bangle is connected to your phone at high speed (7.5ms) maybe there's not enough free time between packets to properly service the EUC?

it is not strange I think. I do not have the bangle connected to the phone, I only use bangle to EUC. I do have hi speed (7.5ms), but this is what I used in all the watches since the dsd6 and it works fine with the modded ones. Using it on the EUC while riding outdoors, is not the same as being static or indoors. Indoors the bangle.s 2 is just fine, I can connect to the EUC even when I am on a different floor, 15 meters away is no problem.

Outdoors while moving is a different game it seems, even some phones to EUC are not perfect, and even good watches like the Garmins when connected to the phone outdoors while riding the EUC, as an extension to the phone, are not really usable.

If you like I can do an rssi comparison but a quick test outdoors, 15 meters away, shows -83 for the bangle.js 2 and -75 for the modded p8. For comparisson, the unmodded magic3 is at -84 and the modded one is at -78.

I will do some more tests on bangle.js 2, maybe my watch got worse over time, or maybe something changed in the software, I will try older version to rule it out, I remember I was happy 2 years back when I first tested it, it was looking really promising, but now I finished the porting of the scripts and the result is not good. But the bangle.js 2 is not bad per se, it is better that stock magic3 in practice, just not good enough for this use case, no watch really is very good, only some p22's are very good out of the box, this is why I opened this thread, because with a simple mod they could be, it is kind of sad.