LowPowerLab Forum

Hardware support => RF - Range - Antennas - RFM69 library => Topic started by: Dirk on August 02, 2013, 02:14:49 PM

Title: starting with RFM69
Post by: Dirk on August 02, 2013, 02:14:49 PM
I am just starting with a few RFM69's. Thanks to the nice library for it, it was no problem to get some signals through the air. But, I have a few questions:

- do you need a vertical wire antenna? Or are there other good options? Maybe even a specific pattern for pcb? Without antenna the signal doesn't even get across the table.

- the examples are called node and gateway. But there is nothing special about the gateway I think? All nodes can communicate with each other without the need for a gateway as far as I understand it now.

- are these devices usable for driving something like an rc car? Or more interesting, a swarm of vehicles? There is probably a correct word for it, but I guess it comes down to respons time. Is it possible to send control signals continuously? Or will there always be a delay or dropped messages?

Title: Re: starting with RFM69
Post by: Felix on August 02, 2013, 02:31:13 PM
As far as antenna goes, you will need some kind of antenna. I use 1/4 wavelength monopole wire antennas and that's how Moteinos ship.

The monopole will yield maximum signal strength when it is straight and perpendicular to the board (not coiled). I think coiling will concentrate the signal but will cause some signal strength.

Node and Gateway are just examples for a sender and receiver, you can adapt those examples or pieces of it to make any node communicate to any other.

You can use them however you want. You will need to use smart code to keep the transmissions short and keep traffic low. High traffic or many nodes will increase chances for collisions. So while you may have 2 nodes with high continuous traffic, adding more may cause some delays because of the carrier sense strategy used in the library.
The RFM69 radios actually support other types of communication which may yield streaming. In my library I am using the packet mode since that includes encryption and packet handling which is something I need for reliable transmission of packeted data.

I encourage anyone to contribute, improve and come up with better/alternative libraries given my starting point.