What is the minimum hardware I need in order to get two Arduinos to communicate with each other over a distance of just 5 metres or so? It needs to be NOT line of sight. I believe that the XBEE shields are no longer available/supported. Presumably I can get some software guidance on this site somewhere, if not some guidance would be welcome.
It needs to be NOT line of sight.
That implies that there will be something in the way. What that something is has a BIG impact on the choices available.
I believe that the XBEE shields are longer available/supported.
Since lots of companies make XBee shields, I find this hard to believe. In fact, impossible is more like it. Sparkfun has XBee shields in stock.
Probably the only things in the way would be things like people walking between the two, or maybe one of the Arduinos moving around the room and facing in the wrong direction. Would XBEEs be the way to go then or is there something more suitable?
Would XBEEs be the way to go then or is there something more suitable?
Personally, I would use XBees, but only because I already have them. At roughly $30 each, and another $30 each for the shields and Arduinos, you are looking at $120 to get two Arduinos talking. Maybe that doesn't matter.
There are cheaper radios.
On the other hand, you haven't said anything about the type of data to be exchanged. You may not even need an Arduino at each end, which would cut the cost considerably.
It's only an experimental project for my own interest and learning. At this stage I just need the moving Arduino to send a couple of dozen or so 'digitalWrite' instructions to the stationary one every few seconds. Nothing too complicated.
GooseBeat:
It's only an experimental project for my own interest and learning. At this stage I just need the moving Arduino to send a couple of dozen or so 'digitalWrite' instructions to the stationary one every few seconds. Nothing too complicated.
The XBee actually has a microcontroller built in. That is what makes it a better choice for a radio, since it can handle retries and all that stuff that makes for reliable communication. What it also has is 20 pins, only two of which are involved in communication, plus two for power and ground. The other 16 are not there to keep the XBee in the shield. They are there to be used as general purpose IO pins, just like the pins on the Arduino. So, depending on how many things you need to connect to the Arduino, you might be able to connect them to the XBee instead, and skip the Arduino(s) and shield(s).
The NRF24L01+ 2.4GHz transceivers are cheap and effective. This tutorial may be of interest.
...R
At this stage I just need the moving Arduino to send a couple of dozen or so 'digitalWrite' instructions to the stationary one every few seconds. Nothing too complicated.
You have not said whether you are ultimately interested in bidirectional communications or if you plan to have only transmit (talk) and receive (listen) with a TX and RX arduino/xbee.
If you are not planning to use bidirectional communication than you could use the basic 310/433 MHz radio modules at a lower cost than the XBEEs. You will need an Arduino for both units and use the VirtualWire communications protocol. If you go this route be sure to purchase a superheterodyne receiver module and not very lowest cost the super regenerative type.
It's only an experimental project for my own interest and learning.
What areas of Arudino programming and hardware you want to learn about? That might help you pick a wireless route. Wireless Buying Guide - SparkFun Electronics
Thanks for all the help, there is now a lot for me to think about. I will have one device (be it Arduino or possibly something else) moving rapidly around. This will be continually monitoring one analogue and one digital input which will be attached to it. This information then needs to be transmitted to a stationary device (I would imagine an Arduino) which will display the results on an array of LEDs.
PaulS:
The XBee actually has a microcontroller built in. That is what makes it a better choice for a radio, since it can handle retries and all that stuff that makes for reliable communication.
Robin2:
The NRF24L01+ 2.4GHz transceivers are cheap and effective.
I'm a fan of both XBees and nRF24L01+ transceivers. The nRF24L01+ transceivers (about $2 each) also have multiple retries (up to 15 by setting the lowest four bits of register 4) when auto acknowledgement is set (register 1).
The nRF24L01+ transceivers can do lots of cool things but I agree XBees are easier to use.
Another easy wireless option is Bluetooth. HC-05 can be either master or slave and at $4 each, it's almost as easy as XBee (possibly as easy though I doubt it's as reliable).
Edit: I don't know what I did to quote myself, but I did. Ignore this one.
DuaneDegn:
I'm a fan of both XBees and nRF24L01+ transceivers. The nRF24L01+ transceivers (about $2 each) also have multiple retries (up to 15 by setting the lowest four bits of register 4) when auto acknowledgement is set (register 1).
The nRF24L01+ transceivers can do lots of cool things but I agree XBees are easier to use.
Another easy wireless option is Bluetooth. HC-05 can be either master or slave and at $4 each, it's almost as easy as XBee (possibly as easy though I doubt it's as reliable).
Duane, have you nothing better to do than talk to yourself ? 
...R
Robin2:
Duane, have you nothing better to do than talk to yourself ?...R
Um. . .
I was demonstrating the nRF24L01+'s ability to automatically send repeated messages?
A more likely story is I'm back from having a crown and the nitrous is still clouding my brain.
Edit: I figured out what I did. I hit "Quote" instead of "Quick Edit".
You could try 2 of these.
http://www.seeedstudio.com/wiki/images/a/a8/HC11_User_Manual.pdf
They are a simple 433 Mhz serial ttl transceiver.
No special coding is needed to use them.
You simply feed serial data in from a serial port at 9600 bps and you get the data out from the other one , ie they act like a piece of wire.
The default state, when delivered is bi directional transparent mode, so whatever you feed in at either end comes out the other end.
For most apps this is all thats needed.
They dont have end to end error checking, or flow control ,so that if you need either you would need to write your own protocol to achieve it.
Much cheaper than Xbees at around $4 each.
Theres also a higher power version the HC-12 which is around $12.
Id use nrf240l+ , they are cheap and good.