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redrok

Senior Member

Joined: 15/09/2014
Location: United States
Posts: 209

Posted: 04:31am 17 Mar 2018

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Hi Andrew;

Andrew_G said Hi Redrok,
BlueTooth is out of my league but I am happy with the little HC-12 units.
I am trying to pack a lot into a small box and was checking (what I suspected) about orientation etc. The responses have helped me a lot. I'll put external antennae on some but not others.

If by "timing" you mean "collision" of data streams - yes I think it may be an issue.
At present I have five remotes sending say 20 ASCII characters (at 2400 baud) every 10 minutes - so it is OK. (There is one other sending data every 10 seconds. That may cause problems so I may have to separate sender and receiver off to another channel).

At present there is no common time-base so even if the start times were staggered clock drift could lead to problems. Given that they sleep for nearly all of the 10 minutes between transmissions I can't see a sensible way of coordinating time.

I guess I could, at say 04:00, broadcast the time (and date) every say 10 seconds until they have all responded "OK Time reset" (or whatever) and then stagger their transmissions (I could also keep the remotes awake longer around 04:00).

For the battery powered remotes it is not critical if I miss a few 10 minute streams of data.

Does that help explain what I am doing?

Cheers, Andrew

Actually I was thinking about a different problem.

This is clearly outside my pay grade also. I just know enough to ask this question.

I believe, and that's a big if. that the actual communications between devices is nothing like what you see doing into and coming out of the ports. Just like ZigBee, and the Internet the input is "packetized" and and sent to the other paired device where the packets are reassemble and stitched together "In Order" before it is outputted.

Bluetooth has full error detection and re-transmission, I think, so the packets can arrive out of order. That's why the "internal" data is always kind of out of sync with time.

Since the data rate is Very Fast you won't, normally, see a problem until it crashes. Again I think.

Off Topic:
When we, Kansas City Space Pirates. were competing for the Space Elevator X-Prize
we needed a precisely timed flashing LED beacon on the climber. We thought ZigBee would be perfect for controlling the flashing. ZigBee is a very robust radio link for long distances. Unfortunately the data packetization effect caused timing regularities. Ya the data was perfect but the timing was not. We reverted back to an old fashion analog radio link which work much better for us.
Back on topic:

So I was thinking when using Bluetooth past it's intended range of 10m or so there could be problems with the handshaking between the paired devices, even when the signal strength was good.

I hope I made it clearer what my question was.
Amy body out there who knows about how this all works???

redrok

Andrew_G
Guru

Joined: 18/10/2016
Location: Australia
Posts: 871

Posted: 05:22am 17 Mar 2018

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Thanks Redrock - I think I understand . . .

I have another detailed question that Rob Rozee may be best to answer?
In Rob's translation of the HC-12 manual it says:

"FU2 mode is an extreme power saving mode, with an idle working current of about
80uA. In this mode, the module only supports baud rates of 1200bps, 2400bps, and
4800bps, with the baud rate in the air uniform at 250,000bps ."
If the module is subsequently set to any other serial port baud rate, the module will not be able to conduct wireless communication normally."

Is that so? I believe that I have been to and from FU2 several times without noticing any problem. Can anyone enlighten me??

Cheers, Andrew

grunto
Newbie

Joined: 07/01/2015
Location: Australia
Posts: 15

Posted: 05:30am 30 Mar 2018

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If you are interested in antennas check out Andreas Spiess' recent video on the subject. Towards the end he talks about some of the issues associated with cheap antennas and also describes some DIY designs.

Andreas Spiess Video

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