I am building a network of devices that I would like to talk to one another.
They will communicate via a bespoke mesh network broadcast protocol.
My problem occurs, as I don’t know a great deal about RF technologies.
I am in the UK and the units will need to ‘talk’ (without a licence) upto ~1km away.
Ideally, they will use either SPI or RS232 or USB to talk to the host system.
Do any canned units or modules spring to mind?
Yes, MaxStream/XBee Pro Series 1 modules. Line of sight, 1kM is do-able with good antennas. Don’t do meshing unless it is essential, you have a lot of nodes (high density) and the nodes move.
Instead, do star or cluster tree.
stevech:
Yes, MaxStream/XBee Pro Series 1 modules. Line of sight, 1kM is do-able with good antennas.
I’ve taken a look at the XBee wireless modules, but I’ve been informed that they won’t really do the job I’m looking for.
I’m after a means of wireless communication that I can place in a self contained plastic box (the smaller the better). This box will have GPS capabilities and will broadcast its whereabouts every second or so. Other units in the area (max of 1km) will pick up this data packet and try to determine where all the other units in the area are in relation to itself.
NB: This unit will be used in the air rather than on the ground.
I’ve been looking at some 9xxMhz and 4xxMhz transceivers, but as yet, I can’t find anything strong AND low power enough.
Does that make things a little clearer about what I’m trying to accomplish?
stevech:
Don’t do meshing unless it is essential, you have a lot of nodes (high density) and the nodes move. Instead, do star or cluster tree.
Due to the nature of the nodes i.e. there could be many and they will almost certainly move, I see no other suitable means of networking them.
I’m thinking of a broadcast system i.e. every unit says “Here I am!” and every other unit hears it.
You might want to look then at the Aerocomm AC4790-1000 modules - they support meshing and have up to 1W RF power output (apparently 20 mile range) in the 902-928MHz band. However in the UK you’d have to check your laws regarding maximum EIRP - if you fall under Europe’s RF laws you will have to reduce your transmit power.
A friend of mine is working on the UAV Outback Challenge here in Australia, using those as his primary communication method from ground station to UAV. So far we haven’t had a single problem with them.
Krogoth:
You might want to look then at the Aerocomm AC4790-1000 modules - they support meshing and have up to 1W RF power output (apparently 20 mile range) in the 902-928MHz band. However in the UK you’d have to check your laws regarding maximum EIRP - if you fall under Europe’s RF laws you will have to reduce your transmit power.A friend of mine is working on the UAV Outback Challenge here in Australia, using those as his primary communication method from ground station to UAV. So far we haven’t had a single problem with them.
Looks good!
I’ve emailed the company, as I’m not too sure if that frequency range is legal to use (without a licence) in the UK.
Good suggestion.
doing 1Km wireless data with simple antennas in an unlicensed band is not viable.
802.15.4 modules can do 1Km line of sight, if you choose the 60mW modules and put a 6dBi or better gain antenna on at least one end of the link. I’ve done it. Can’t beat the cost.
Next step would be 902-928MHz in No. America using, say, Digi/Maxstreams XTend modules. But in the UK, you may need an 868MHz version.
Oh dear! That’s not good to hear.
What range do you think I could get with the (legal) technologies available then?
My ideal solution would be a small wrist worn device that can ‘talk’ to several other devices via broadcast packets.
All devices will broadcast at ~1Hz, and all devices will have to successfully receive every other device’s broadcast.
Any suggestions?
Aerocomm AC4790-1000 - This looked great, but we’re not allowed to use it in the UK.
Aerocomm AC4868-250 - Is the solution I could use and is legal, however, it uses a client/server protocol.
Aerocomm AC4424-100 - Higher frequency, but same as above.
In that case you’ll have to wait until the XBee Pro v2 is released - if the UK has the same laws as we have here on the 2.4GHz band (max 4W EIRP with min 72 frequency steps with adaptive frequency hopping) then you’ll be able to use it fine.
I just checked http://www.digi.com/products/wireless/z … module.jsp and apparently it’s already released and approved for use in Europe, except you’re restricted to 10dBm transmit power (at 17dBm it gives 1 mile range apparently). However, it does support meshing, weighs next to nothing and costs $34 - so it may be worth investigating how well it performs on your aerial platforms even if it doesn’t meet your maximum range requirement. Remember, that range is point to point, so even if your nodes are spread out over many kilometers, as long as each node is within range of another node it will still communicate with the mesh network.
Krogoth:
In that case you’ll have to wait until the XBee Pro v2 is released - if the UK has the same laws as we have here on the 2.4GHz band (max 4W EIRP with min 72 frequency steps with adaptive frequency hopping) then you’ll be able to use it fine.I just checked http://www.digi.com/products/wireless/z … module.jsp and apparently it’s already released and approved for use in Europe, except you’re restricted to 10dBm transmit power (at 17dBm it gives 1 mile range apparently). However, it does support meshing, weighs next to nothing and costs $34 - so it may be worth investigating how well it performs on your aerial platforms even if it doesn’t meet your maximum range requirement. Remember, that range is point to point, so even if your nodes are spread out over many kilometers, as long as each node is within range of another node it will still communicate with the mesh network.
Note that the XBee “Series 2” modules use Ember’s chipset whereas Series 1 (the original) uses Freescale. I’m told by Digi that the series 2 modules are ZigBee only. Most applications don’t need / want the complexity of ZigBee.
stevech:
Most applications don’t need / want the complexity of ZigBee.
Quite!
When I ran the idea of using ZigBee through a friend, they told me that it doesn’t suit my application.
All I need is a small, simple, broadcast communication solution that I can use over distances of <1Km.
There’s me thinking this kind of thing was going to be easy. 
I found this over the weekend: http://www.gpsflight.com/Main/ST900%20Overview.htm
The module this unit uses is the sort of thing I’m looking for.
However, that frequency range isn’t legal in the UK without a license.
ljkenny:
stevech:
Most applications don’t need / want the complexity of ZigBee.Quite!
When I ran the idea of using ZigBee through a friend, they told me that it doesn’t suit my application.
All I need is a small, simple, broadcast communication solution that I can use over distances of <1Km.
There’s me thinking this kind of thing was going to be easy.
ZigBee is not 802.15.4 though some use the terms interchangeably.
As I said earlier - 1Km with simple rubber-ducky type antennas is not practical in unlicensed bands.
stevech:
As I said earlier - 1Km with simple rubber-ducky type antennas is not practical in unlicensed bands.
What sort of distances would you class as practical/realistic?
Maybe the product line of http://www.bigredbee.com/ contains something you can use. It seems that their transmitter can be modified to a legal frequency for your country (somewhere in between 300 and 900MHz).
Unfortunately, that unit requires an antenna which is unpractical for my use.
ljkenny:
I found this over the weekend: http://www.gpsflight.com/Main/ST900%20Overview.htmThe module this unit uses is the sort of thing I’m looking for.
However, that frequency range isn’t legal in the UK without a license.
Actually, that device (www.gpsflight.com) can work with any type of radio, including the zigbee radios from Digi. Just order the unit with no radio, and plug in your own.
The idea is to make a unit like that specific for skydivers, rather than buy it off the shelf.
What kind of university project would that be? =:-)
jandirks:
Maybe the product line of http://www.bigredbee.com/ contains something you can use. It seems that their transmitter can be modified to a legal frequency for your country (somewhere in between 300 and 900MHz).
Actually ‘line of sight’ is the key. I have used the 100mw digi radios and have gotten well over 25 miles line of sight with simple 6" antennas in the 900mhz range and more than 1 mile with the high power zigbee radios with nothing more than wire antenna. The trick is line of sight and keeping the fresnel zone clean.
Ham radio stuff that sends data over voice links can work like the bigredbee stuff, but that method is really not optimal for data given the comparatively poor db involved in voice links compared to data links. For example, the digi radios can deliver data out to -110db, and you are very lucky to get -70 with a voice link.
Clearly working in lower frequencies like 200mhz if you have a license can get you better range at the same output power, but at a much lower data rate. A ‘ham link’ in these lower frequencies will allow much longer range when not ‘line of sight’.