Have a little project on the go and need a wireless link max 1-2km. I was originally looking at using a RFM23Bp but there doesnt seem to be a lot of info and code around for it that I can modify/learn off to work out what to do. There is a bit more info on the RFM22 but i dont think im advanced enough to understand it all!
The project is very simple, An arduino at one end with a moisture sensor, when it gets wet, it sends a signal wirelessly to and arduino at the other end which sets off a buzzer.
Fairly simple i would think, but am unsure how to tackle it.
Im a noobie, but can manage to copy/modify code to get things working.
Whatever transceiver you consider, get one that complies with your (legal, range...) requirements, and that comes with Arduino libraries and example code.
Wireless transmission depends on sender power and antennas. A good antenna is the best signal amplifier, look also what antennas are suggested and offered for the transceiver, where to mount the antennas of the transmitter and receiver (outdoor, roof...). For point-to-point transmission, between stationary transceivers, directional antennas will be the best choice - if available.
Where I live, i Can transmit on the 915-928mhz range up to 1w.
But I cannot transmit on a sinlge frequency. See the wording below
Frequency hopping transmitters
915–928
1 W
A minimum of 20 hopping frequencies must be used.
So I was just wanting to make sure that in the RF module I end up buying, it can be in the code somehow that it can use programmed hopping frequencies to make everything legal.
Have a look on the RFM69 as well, there is a standard and a high-power version. They also include AES-128 encryption via hardware, which I think is a great feature: http://www.hoperf.com/rf_transceiver/modules/RFM69W.html. You should be able to find the module from $5-$6/unit.
The only thing you need to pay attention if you wish to build the module yourself is that those modules, and also the LoRA RFM95, they're 3.3V only, so connecting to a 5V Arduino is very likely to produce the magic white smoke
Regarding the frequency hoping, transmission power, etc. You'll need to find the local regulations, I wrote a small summary and provided the link for US, Australia and Europe here. In your project will run in an open area, is very likely you'll need just a few mW of TX power as those modern radios have high RX sensibility.
Also an option to me is 433mhz. But i am limited to 25mw, but i do not have to worry about frequency hopping in that band. So that may make things simpler
Also, if you plan to transmit only short messages with significant time between each instead of continuous transmitting data, you might not have to worry at all.
Yes, what im planning, will only transmit for only a second or two, every 15-30 mins.
How am I suppose to work out whether that complies?
If this is a one-time project for your own interests, I suggest not to worry about "complying". It is extremely unlikely that such a low power, low rate transmission, in a legal ISM band, will interfere with other services.
If this was a private project I wouldn't even worry. But it's a proof of concept for potentially a commercial application. So I need to know it will be ok if sold.
The RFM69 433MHz module actually works from 424Mhz to 510Mhz, so it can be used on the 433MHz band or this special band mentioned above and available here in Australia. But as jremington mention you probably need some legal advice and very likely certification for C-Tick and RCM if you plan to commercialise a final product in Au.
