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Cheap Wireless modem, Zigbee or what?

Hey all,

I was asked this week if I could come up with something simple to trigger an alarm light in a noisy industrial environment. The direct distance is only around 80 metres, but it's around a corner (approx 60

  • 60 metres walking) and there are quite a lot of large 3-phase motors and inverters etc. in between.

Just FYI, I have a pair of Jaycar 433Mhz modules and a pair of Oatley modules, also a pair of these

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These modules are for my own use (if we ever get a rainy day again :-), and given that I don't want to spend my own (unpaid) time and components, making circuits, writing code and testing comms, thought I might ask you guys if there are any cheap alternatives around.

I've done some simple stuff with AVRs (using GCC as a compiler), but again don't have the time to implement comms with error correction - ie. manchester encoding, so instead thought something like an ATtiny13 interfaced to a radio modem may be the way to go, something like this...

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I notice that this has - from a blurry magnification, an ATMEGA-something chip onboard (probably for comms only).

One problem I've found - after Googling for quite a while now, is that although they have radio modems, resellers (especially in Australia) appear to be a bit embarrassed with the prices of these units, and thus don't show them. I could request quotes, but really, I just want to see prices and buy the effer! Other good places like Dontronics and Futurlec don't seem to carry anything appropriate.

The other way I could go is to try starting out with Zigbees so that I have a basis for future data aquisition, but not a cheap way to go I think.

Anyway, enough of my rambling. Any thoughts people?

Cheers, Phil.

Reply to
Phil
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The big guys like Telstra etc plan their RF links before implementation.

They know what is

- The minimum RF signal level required at the receiver for RELIABLE valid data.

- What are the path losses from the transmitter to the receiver

- Add in a loss fade margin.

Based on the factors above the can compute the minimum transmitter power.

A signal fade might be if a big truck parks between the transmitter and receiver and reduces the signal. OR A near by transmitter reduces the receiver sensitivity.

RF losses through walls and other structures are a significant factors.... transmitter / receiver ranges quoted in "open free space" and severely reduce through structures.

If you just have a transmitter and receiver - what happened if another transmitter in the 433MHz courpts the signal.. Will you send additional redundant data to make sure the transmission goes through.

Will you use 2 transceivers and send data and wait for reply.

Reference: Electronic Communication Techniques (Young)

At 433MHz the Australian legal limit is 25mW EIRP... hence you can deduce what the range might be like, knowing the other factors.

Just a few thoughts.

Joe

Reply to
Joe G (Home)

Simple - that would be a piece of cable wouldnt it ?

I would not bother for this application just keep transmitting the Light status continually

It may be a nuisance running 80 M of cable but by the time you write the code etc for the AVRs and worried about interference, Antennas etc I suspect that running a length of cable may not be such a drama after all especially if there are cable trays etc - current loop or contact closures are pretty reliable

Reply to
Richard Freeman

Hi Joe,

Thanks for your thoughs. Much appreciated.

Well, after more searching I'm still thinking that these may be the way to go.

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and combined with a simple ad hoc network protocol with 'station ID' checking. Because these modules do all the low level data checks this will make coding easier and more compact for the smaller AVR micros..

Something like...

  1. Station 1 sends to Station 2 - AVAilable?
  2. S2 sends ACK to S1 - AVAilable YES/NO - OR NAK
  3. S1 to S2 - CMD + ReaDY? - Switch relay 1 ON
  4. S2 to S1 - VERify + AVAilable YES/NO + data_received ^
  5. S1 verifies original_data against data_received
  6. If data OK, S1 sends EXEcute to S2
  7. S2 switches relay ON and sends OK message to S1

Simple ASCII data would probably look like...

  1. S01S02AVA
  2. S02S01YES
  3. S01S02CMDRDYDO001ONN
  4. S02S01VERAVAYESS01S02CMDRDYDO001ONN
  5. Data S01S02CMDRDYDO001ONN == S01S02CMDRDYDO001ONN, so OK.
  6. S01S02EXE
  7. S02S01OKK Now, these are just some initial thoughts, probably some wrong ones.

I may have example code for a simple State Machine already (somewhere in my collection).

Cheers, Phil.

Joe G (Home) wrote:

Reply to
Phil

Hi Richard,

Thanks also for your reply. Indeed the voice of reason.

Just to explain how this idea came about. After years of coding business software my new boss decided that my electronics hobby may be put to use at work, and damn, do I need to do something different at work! Yes, we could just call the 'leccos' and ask them to run cable, and maybe I could take some photos of them doing it for posterity :-). That would be fine (and quick), also wiping the teardrops off my keyboard would be an easy task ;-(

Just kidding, really your thoughts make much more sense.

Thanks, and regards, Phil.

Richard Freeman wrote:

Reply to
Phil

I would expect the call should be made a licensed cabler , most sparkies don't have a suitable ticket , and for the small fee a cable would expedite matters considerably .

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will provide you with a suitable person in your area

Reply to
atec 77

suspect

especially

I've got to agree, in both video and comms I've often looked at and tried wireless solutions, and the overwhelming conclusion is that in any situation where it's possible to run a cable, you should run a cable.

Reply to
Poxy

Well If the cable is not connected to power distribution or Telecommunciations network then does the sparky/whoever runs the cable really need to be licensed ??

Reply to
Richard Freeman

The law says if the cable is connected to or MAY be connected to the telephony system the installer must be licensed If you have any further query perhaps you should ring the Govco Dept .?

Reply to
atec 77

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