DIGIMESH - RF Sync Signal effect on ON / SLEEP Line (XBEE)

Wireless & IoT
1

I am building a very time sensitive wireless application. I am basing it around the XBee as my wireless device and having a field wide accurate sync pulse would be very helpful. I was originally designing around point to point 802.15.4 and using point to point and doing piecemeal PINGs in order to get my timing. However, after talking to a digi engineer I found that if I moved to digimesh they have a very low level RF ping they do site wide that takes into account time delays as it moves around the mesh already built in.

I also found out that when this tightly controlled sync signal goes around it ‘blips’ pin13 (ON/ SLEEP output) and I could do my microcontroller sync based on that. However, this blip of that line is completely undocumented. This info came straight from one of the engineers who actually designed the digimesh protocol.

Do you guys know when this blip happens and what it looks like (edge conditions, HIGH/ LOW time, anything like that?) He wasn’t super specific, but he said I could scope it and find out. I’ll work on it this weekend but thought maybe one of you guys already knew the answer.

Thanks.

2

How accurate do you need these synchs to be?

802.15.4 is a CSMA/CA media.

You can do a broadcast from one to many (MAC address FFFFFF…) and all may receive the signal simultaneously.

Of course, there’s GPS and 1PPS to synch

3

I need to have an accuracy of about +/- .0004 preferably.

I’m starting to wonder if I have any chance of doing this with the XBees.

GPS timing would completely blow the budget…so that’s out. Plus they are often mounted indoors, so signal may be questionable.

4

accuracy of about +/- .0004 preferably

seconds?

I don’t think that XBees would work.

Maybe a simple OOK transmitter/receiver can be modulated with a time sync signal.

5

waltr:

accuracy of about +/- .0004 preferably

seconds?

I don’t think that XBees would work.

Maybe a simple OOK transmitter/receiver can be modulated with a time sync signal.

Yeah, you may be right.

On that note, can you recommend a good Trans/ Rec company/ model for my purpose? I need multiple frequencies, long range, low bandwidth

I found this stuff, but it is based out of Europe. http://www.cdt21.com/products/tx_rx/default.asp Have any good recommendations of your own?

6

Just checking DigiKey and found these:

http://search.digikey.com/scripts/DkSea … 23SK868-ND

http://search.digikey.com/scripts/DkSea … L-MS-ES-ND

http://www.linxtechnologies.com/Documen … _Guide.pdf

http://search.digikey.com/scripts/DkSea … -418-LR-ND

or something from this:

http://search.digikey.com/scripts/DkSea … %20modules