[TriEmbed] Long range digital communication (long range wifi, XBee?)

Thu Oct 25 16:17:46 CDT 2018

Hmm.. I pasted this to the wrong stream I think.  Sorry if this is a duplication

I would suggest using a 900Mhz base station someplace on the property where there is an RF view to the rest of the property.  You are allowed 1 watt with a frequency hopping system.  Then use stations in the robots and wherever your control system is, all within almost line-of-site with your base station.  You can get 100kbits/sec shared bandwidth.  you’d have your base station set up as a channel control device offering up time-slots to your mobile assets and the control station.  If you had 2 robots you’d probably end up with 2000 or 3000 bytes per second per robot, split between robot transmissions and robot receptions. 
Part 15.247 FCC rules I think.

no cost for operation.  

This isn’t going to work for full motion video but snapshots should be possible and you can do reasonably high speed navigation with GPS, sonar ranges and Remote Control motor management in real time with this kind of system.  

Vendors:
Search the web for 900mhz spread spectrum radio”    You’re looking for 15.247 I think if you need to narrow the search. 

This can be in-house manufactured too depending on your volume.  There are plenty of single chip 900 radios.  Many of the LoRa radios can be used in FSK mode for this but you’ll need a PA to get the range you need I think.  In the short run you can do in-house testing with bare modules based on the SemTech 900 radio-on-a-chip if you want to go it from scratch.  

FHSS rules are that you can stay on one frequency for up to 400mS, you generate your own transmit sequence and apply it in every device.  You have to hop through 25 or more frequencies.  You can repeat every 20 seconds.  The base station would send some synchronization info every time it ends up on your hop sequence channel 0 or something like that.  Any device which has lost the FHSS sequence index would camp out on channel 0 until it hears the base station send out the synchronization info.   

     Tadd

Tadd / KA2DEW
tadd at mac.com
Raleigh NC  FM05pv

“Packet networking over ham radio": http://tarpn.net/t/packet_radio_networking.html <http://tarpn.net/t/packet_radio_networking.html>
Local Raleigh ham radio info: http://torborg.com/a <http://torborg.com/a>  

> On Oct 25, 2018, at 3:23 PM, Charles West via TriEmbed <triembed at triembed.org> wrote:
> 
> Hello!
> 
> I'm in Lansdale, PA now but I was hoping I might be able to pick you guy's brains.  My current big project is trying to build one or more robots to deliver food/drinks on golf courses.  I'm currently trying to figure out the best way to maintain continuous(ish) contact between a access point/basestation at it's base of operations and 1 or more robots operating on the course.
> 
> At a minimum, I would like to have the robot report its basic status (battery percent, GPS position) but it would also be great if it could stream video when required to allow teleprescence steering or determination of what is going on.  The robot would probably be about 1 km from the base station at max. 
> 
> I'm currently considering 3 possible solutions but I'm pretty open to ideas:
> 
> 1.  Use a mobile hotspot/cell modem:
>         For fixed $130 and monthly $20, I can get a mobile hotspot which provides one gig of data per month and more data for $5/gig.  If I keep the reporting really light, this could work but the communication would have to be kept pretty limited.
> 
> 2.  XBee:
>          These modules seem to float somewhere between $25 and $60 in prices, so a pair would be somewhere in the $50 to $120 range.  Sparkfun had a good guide to XBee (https://www.sparkfun.com/pages/xbee_guide <https://www.sparkfun.com/pages/xbee_guide>) but they are listing almost all of their products as retired (besides old series 1) and most of the stuff I read about XBee is from 2015-2016 so I am not sure what the best options are anymore.  In any case, it looks like it would provide a low baud rate connection over the desired range.  The main problem is that it requires working through XBee and making my basestation have to have special software to forward information.  I'm also not sure about security and it is certainly not going to be streaming video.
> 
> 3.  Long range Wifi:
>         Rodney's done some work in this area before with his weather balloon projects.  I don't recall off the top of my head how far he managed to get but I do remember he had to use higher power than allowed without a higher grade amateur radio license.  That power level would not work for a commercial operation.  There are some companies that are selling solutions aimed at farms (http://ayrstone.com/www/?v=7516fd43adaa <http://ayrstone.com/www/?v=7516fd43adaa>) and there seem to be off the shelf solutions that can get 500 ft (mostly aimed at hotels).  The hotel systems seem to be in the $350 range and the farm systems in the $500 or so.  The robot could use a high gain antenna, but it is not clear how much it helps.  These systems have security built in and potentially can stream video if the range is long enough.  Like hotspots, writing software for them would also be easy.  
> 
> What do you guys think?
> 
> Thanks,
> Charlie
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