Wireless communication

Started by Igor Janjatovic October 7, 2005
Hello,

I'm looking for RX+TX wireless communication module with following
requirements:

- 3.3V operation,
- low power,
- small package (for example: 50x50mm)
- global frequency standard (2.4 GHz I guess??),
- up to 1000m range,
- can be configured for multidrop networking,
- simple interfacing to PIC MCU with no significant code overhead,
- baud rate is not critical.

Any ideas? Links, manufacturers, standards... anything? :-)

Regards,
Igor
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Hello Igor,

Did you consider Zigbee?
See www.maxstream.net
There are Zigbee modules with running at low speed.
UART interface has 115200 bps with simple communication.

Regards,

Mada. ----- Original Message -----
From: "Igor Janjatovic" <kodrat@kodr...>
To: <piclist@picl...>
Sent: Friday, October 07, 2005 3:24 PM
Subject: [piclist] Wireless communication > Hello,
>
> I'm looking for RX+TX wireless communication module with following
> requirements:
>
> - 3.3V operation,
> - low power,
> - small package (for example: 50x50mm)
> - global frequency standard (2.4 GHz I guess??),
> - up to 1000m range,
> - can be configured for multidrop networking,
> - simple interfacing to PIC MCU with no significant code overhead,
> - baud rate is not critical.
>
> Any ideas? Links, manufacturers, standards... anything? :-)
>
> Regards,
> Igor >
> --
> No virus found in this outgoing message.
> Checked by AVG Anti-Virus.
> Version: 7.0.344 / Virus Database: 267.11.13/123 - Release Date:
06.10.2005.
>
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> Did you consider Zigbee?
> See www.maxstream.net

That was my first choice but since I never used any of wireless technologies
I thought that it might be good idea to ask about this.

Thanks,
Igor
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No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.344 / Virus Database: 267.11.13/123 - Release Date: 06.10.2005.


--- In piclist@picl..., "Igor Janjatovic" <kodrat@p...>
wrote:
>
> Hello,
>
> I'm looking for RX+TX wireless communication module with following
> requirements:
>
> - 3.3V operation,
> - low power,
> - small package (for example: 50x50mm)
> - global frequency standard (2.4 GHz I guess??),
> - up to 1000m range,
> - can be configured for multidrop networking,
> - simple interfacing to PIC MCU with no significant code overhead,
> - baud rate is not critical.
>
> Any ideas? Links, manufacturers, standards... anything? :-)
>
> Regards,
> Igor >
> --
> No virus found in this outgoing message.
> Checked by AVG Anti-Virus.
> Version: 7.0.344 / Virus Database: 267.11.13/123 - Release Date:
06.10.2005.
>

Some things aren't immediately obvious when looking over the large
range of devices available for this.

You haven't mentioned connecting to a PC, so you could effectively
rule out devices classed as 'rf modem' . This is because mostly they
have a built in RS232 connector and firmware to deal with the data
transmission, which all just adds cost. You haven't mentioned if
your data is two-way or one-way (duplex or simplex), I've mentioned
both a little bit

2.4GHz is a good, if not busy, band to use. Before picking your
final solution it's a good idea to try to get the use of a radio
scanner or a receiver for the frequency which you hope to use. You
could lose hours of quality time tracking down a fault with your
design only to later discover that it is interference.

Looking at www.rfsolutions.co.uk as an example of a supplier (I
have no connection with them !) they sell small rf modules with
ranges rating upto 100m. These are cheap from most suppliers, and if
you are going to transmit a small ammount of data and the range
isn't quite 1000m, and assuming you have a clear line of site, then
the effective ranges can be increased by using a high gain receiving
antenna.

The antenna and it's position are so critical to the effectiveness
of a communications link that they're worth a mention. If you take a
pair of 'average' 2.4GHZ transceivers with small helical antennae,
put one in your house and one in a friends house 300m away, there is
a good chance that in the average built up area you won't get any
signal at all between the two units. Even 100m could be hoping for
too much if there are other strong 2.4GHz units in the vicinity, and
a few leaky microwave ovens for good measure.

If on the other hand you position your units on facing windows of
the two buildings things can get that much better because there are
fewer internal walls for the signal to travel through before getting
out into the open space outside. But if you take a piece of coaxial
cable from each unit and run it up to the loft, or even outside the
house at the highest point and remount your antennas there you will
realise a far superior and more reliable link. There are even yagi
type antenna's which look like small tv aerials, which are
incredibly directional because they work to focus the signal in one
direction more than any other. A pair of these pointing at each
other could extend the quoted 1000m range to 2000m or more. I'm not
sure about the legality of using such high gain antennas though, on
a lower frequency band, the 433MHz public access band has a
restriction for transmitting antennas to produce no gain in signal.
A Yagi antenna produces significant gain.

Your biggest enemy is going to be noise and restrictions on the
location of the antenna.

Looking at the RFsolutions site , at the 'smart radio ' tab they
offer 433MHz units with a 250m range. These are slightly better than
the basic radio modules shown in the tab above them because they
deal with things like handshaking,data encryption and other host
interface functions.

You can use the smaller radio modules which are generally the
cheapest way of all but you need to be aware of a few things. Your
data may need to be encoded using 'Manchester Encoding' in order to
make the link work properly. Thius is simply a way of encoding the
data such that there is a lower likelihood of there being a data
error caused by interference at the receiving end.

I used a pair of those basic modules, which cost less than 8 for
the pair and with good antenna design and placement exceeded the
range and got a good reliable link. I needed to add data checking
routines to the serial routines in order to create and validate a
checksum, which is where something like the Smart Radio products
come to the rescue. Bear in mind that they're true 'transceivers'
meaning that they combine a transmitter and receiver on one board to
become one half of a two way link. Using simple modules you need to
buy separate transceiver and receiver modules.

It doesn't make sense to overspend on products you don't really
need, remember that if you can get physical access to high points of
buildings you can mount the transmitter there and feed it the data
signal from a 3 core cable carrying Vs, Gnd and Data wires with a
really short length of coax to the antenna. if it's made in a
waterproof enclosure you can have a brilliantly reliable system up
and running for very little outlay.



Hello Chris,
 
> Some things aren't immediately obvious when looking over the large
> range of devices available for this.
 
True. Amount of information is overwhelming. Those dbm's and dbi's are especially confusing but I figured out 'what is what' :-)

> You haven't mentioned connecting to a PC, so you could effectively
> rule out devices classed as 'rf modem'.
 
Yes, I realized that after visiting few web sites. I'm looking for OEM module since it is supposed to be connected to PIC. I decided to go with ZigBee, as Mada Jimmy suggested (thanks Jimmy!), and it was my first choice so I guess it's OK.
 
> You haven't mentioned if
> your data is two-way or one-way (duplex or simplex), I've mentioned
> both a little bit
 
It is half duplex.

> 2.4GHz is a good, if not busy, band to use. Before picking your
> final solution it's a good idea to try to get the use of a radio
> scanner or a receiver for the frequency which you hope to use.
 
Good point. I will place order for ZigBee development kit and then test it to see if band is busy, as you suggested, and also to check range outdoors, since it's for outdoor use.

> Looking at  www.rfsolutions.co.uk as an example of a supplier (I
> have no connection with them !) they sell small rf modules with
> ranges rating upto 100m.
 
MaxStream seems to have very nice solutions with ZigBee networking, which means that most of the things that you mentioned as critical are already implemented. Module is controlled through simple AT commands and it handles package delivery with buffer for undelivered packages and reliable retry algorithms. Hopefully that should do the trick. I will check ZigBee specs, just in case.

> The antenna and it's position are so critical to the effectiveness
> of a communications link that they're worth a mention.
 
I am aware of that but since it's for outdoor use plus MaxStream has few very nice articles about Fresnel zone and antenna efficiency, I guess I'll be OK with this. I decided to go with antenna from Nearson, which seems to be stable manufacturer.
 
> I used a pair of those basic modules, which cost less than 8 for
> the pair and with good antenna design and placement exceeded the
> range and got a good reliable link.
 
Sounds great although I was looking for 'world wide' standard and 2.4GHz sounds like good choice. There is 100mW limit on output power in Europe but it's OK since I have 18 dbm module and with 2 dbi antenna I get 100mW of output power so it fits. This power is supposed to provide up to 1.6km range (outdoors, LOS), but since I'm OK with 1km max, I hope it will be OK.
 
Thanks for these advices. I really appreciate it. If you are interested in XBee-PRO modules I can let you know about the results once I test them? Seems like nice solution for wireless applications...
 
Best Regards,
Igor


--- In piclist@picl..., "Igor Janjatovic" <kodrat@p...> wrote:
>

>
> Thanks for these advices. I really appreciate it. If you are
interested in XBee-PRO modules I can let you know about the results
once I test them? Seems like nice solution for wireless applications...
>
> Best Regards,
> Igor


They'll do very well for you I'm sure !

Of course, any information from users not related to the manufacturer
would be very welcome :)

Chris



> Of course, any information from users not related to the manufacturer
> would be very welcome :)
 
What manufacturer??? :))
 
Regards,
Igor
 
P.S.
The only company that I'm related to is my own company (KODRAT electronics) but, as you probably noticed, I don't advertise on groups.


--- In piclist@picl..., "Igor Janjatovic" <kodrat@p...> wrote:
>
> > Of course, any information from users not related to the
manufacturer
> > would be very welcome :) > What manufacturer??? :))
>
> Regards,
> Igor
>
> P.S.
> The only company that I'm related to is my own company (KODRAT
electronics) but, as you probably noticed, I don't advertise on
groups.

What I meant, was pretty much what it says.
I can look at a manufacturers website and hear what they say - but an
opinon from someone not connected with them is going to be at least
as objective as the maker's opinion.

There was no intimiation that you were connected with them, trust
me :-)
Chris