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Hi Everyone,

I'm trying to work out the logistics of networking a large number of Arduinos via a wireless method that would ideally approximate something like RS485 (i.e. addressing lots of individual nodes based on IDs). I've got quite a bit of wired networking experience but have only ever wirelessly interfaced between with one arduino and a laptop over a bluetooth serial connection (which worked very nicely).

Ideally I would like to have around 50 nodes on the network, though if this is impossible I would consider lower numbers. All of which should be able to receive and possibly send serial data. The bandwidth can be pretty low, updating maybe only at 1-10Hz. I'm really not sure if this is possible with bluetooth, or if it is, if it would be painfully slow to initialise all those virutal serial ports and might make comms really sluggish. I'm initially envisioning a latop as the master, though it would be great to replace this later with some embedded hardware.

I'd love to hear your suggestions on this problem and am totally open to ideas regarding other wireless technologies than Bluetooth (Wifi, Xbee etc.)

Many Thanks,

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So work up a wireless protocol where everyone listens, and when commanded only sends an amount of serial data - can be a predetermined amount, a commanded amount, an indefinite amount but with the amount that will be sent included in the response. Everyone else just listens for when they're commanded to send something. Maybe a master-call, slave-ack, master-call, slave-send, master-ack:

Master: Slave #3, you alive have data to send?
Slave #3: yes, 8 bytes to send
Master: Slave #3, send 8 bytes
Slave #3: sends 8 bytes
Master: Slave #3, data received
Slave #3 then deletes the data & preps for next data

Could also end with:
Master: Slave #3, resend the data
Slave #3: sends 8 byte
Master: Slave #3, data received
Slave #3 then deletes the data & preps for next data

Technology depends on how far you want to send.
434 MHz.  2.4GHz such as nRFL2401+. Frequency hopping DNT24P. etc. Other types as you've mentioned.
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Hi,

The serial protocol itself isn't so much of a problem, it's more about choosing hardware that would enable all the nodes to connect to the same master. So if each Arduino was equipped with a Bluetooth module would it be possible for them all to listen to the same transmission? Would they all pair with the same serial port on the master device or would they each require they're own COM port? Managing 50 virtual serial ports sounds like it could cause problems and be slow to initialise. I'm imagining the connectivity would be different with other technologies...

I think all the nodes will be within a 10-20 meter radius.

Cheers,

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If missing a few transmissions isn't a major concern, you could go with some of the basic RF modules out there.

JeeLabs has some good, cheaper hardware for this. They also have a nice simple library to use with the HopeRF transceivers.
« Last Edit: August 29, 2012, 02:48:15 pm by Arrch » Logged

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May I suggest Freakduino Chibi boards, are Arduino compatible boards with an Atmel 2.4 GHz radio installed.

Regards,
Dario.
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