Quote

2. From a PC or other embeded board I would like to transmit a command to
all the 20 Arduino fios and get them to respond with the data.

4. The Ardunino Fios will be in sleep mode and wake up and transmit their data and go into  sleep mode
every 30 minutes.
You say that the data needs to be broadcast in response to the request for data. The Arduino and XBee have to be awake to receive that broadcast.

Before choosing hardware and sleep modes, you need to get your requirements straight.

Hi, I forgot to remove point #2. as I was typing the message.

My idea is this..

A. FIO should wake up every 30 minutes ( the XBEE should stay sleeping)
B. FIO checks for light, no light? goes back to sleep , if light detected FIO wakes up the XBEE and transmits
    puts the Xbee to sleep and goes into sleep mode.


Allan

If you are wanting the end devices to AUTOMATICALLY respond with data without any arduino sketches
then you have to consult the Xbee manual. and use the Xbee config program.

however if you have the ALL the XBEE connected to Arduino or other microprocessors, you have to
send your data in such a way so that the end device knows the message is meant for them as each
xbee has an address.

You should use the AT command  set to send out a broadcast /unicast.
Then the other 2 Xbees are also in AT command mode and your Sketch must wait for
the data to come in. When the command is received, the other 2 Xbees send their
response using the AT command set back to the coordinator.


You would need a ring buffer in your coordinator sketch to store the data
as it comes it quite fast. you then check your ring buffer to see if there
is anything to process.

Your solution is in this thread below
http://arduino.cc/forum/index.php/topic,104648.0.html

see how people are using it.
http://arduino.cc/forum/index.php?topic=61238.0



Allan

Hi
 Yeah the 433 mhz is a good option.. you mean it has automatic repeater
function built in? This means I can simply power up some rfm22s and leave
them repeat signals around blind spots? Thanks for the tip, I will study it
carefully.

I stil would like to hear what the Xbee Gurus say about my requirements.

I went to the WASPMOTE product web page. Seems they
have an impressive range of 'plug and play' solutions. however
its very pricey and my farmer has an end of life for this project
of 2 years.

http://www.libelium.com/products/waspmote/hardware


Regds
Allan

Hi
 I need help in  choosing an XBEE 868 MHZ part so that I can
solve the following problem. I am new to XBEE..

I have a small farming prototype which I am going to choose
the arduino FIO.

I chose 868 mhz for long range and low transmit power.
my data can be as slow as 1200 baud.

1. I would have 20 Arduino fios with some soil and temperature sensors
and light level sensors.


3.0 I would like to try to change batteries every 2 months or longer if possible.

3.1 I would be using alkaline batteries
 (FIO is limited to 3.3 volt but the FTDI cable is actually providing 5 Volts so 3 D sized
alkaline batteries providing 4.5 volts when new should work? or should it be 4 D
sized providing 6 volts when new?)

4. The Ardunino Fios will be in sleep mode and wake up and transmit their data and go into  sleep mode
every 30 minutes.

4.1 transmission would be turned off when no light is detected using a LDR (nighttime)
if growing lights are turned on, the transmission will start again since I am also
measuring light levels.

5. The main receiver would have a very large battery or is AC powered, like
a LAPTOP.

I understand XBEE 868 digimesh is a restricted export controlled product.
so I would like to avoid that as much as possible.

I am counting on the long range of the 868 mhz to avoid having to buy
digimesh based products that can self repeat infomation.

My terrian would have some small undulations on it as it is a farm
in a hilly area. Range would be about 1 kilometer square.

Which XBEE 868 model can I choose to make this successful?


Allan