I have a question regarding RF serial communication.
Basically, I am building five Arduinos that are equipped with RF transmitter/receiver pairs that are wired to the Arduino’s Rx/Tx pins. I want these 5 Arduinos to be able to talk to one another, and have tried the Laipac 434A RF pair (http://www.sparkfun.com/commerce/produc … ts_id=7815).
The setup works only when there is one transmitter module connected, i.e. only one Arduino serves as the broadcaster, while the others only have their receivers connected. If I were to try putting the transmitter modules in, the first Arduino’s RF signals will not be picked up by the others.
edit: I’d like to add that the requirements for the serial communications are really low; all I am sending between the 5 Arduinos are simple serial strings that do not need to have a very high transmission speed.
The Mirf2s have a carrier sense circuit. This detects ambient RF on the assigned frequency and can wait until it is clear to send. Using multiple transceivers, this helps keep data collisions from happening. It sounds like this is what you need. Range on 2.4 gig is more limited than 434, but these guys are neat. Right Brennan?
when you get to $20 or more for a data transceiver, you are at the cost threshold where you could opt for an 802.15.4 module for the same cost. And all the protocols for transmission, addressing, error correction, and if you wish, meshing, are included. Also, there are many vendors for these standards-based modules, so you benefit from the competition.
MaxStream XBee and XBeePro have been the price and volume leader, but there are at least 12 others. Panasonic and OKI are in the same price area. All are sold by Mouser, DigiKey and others. I wish SFE would sell some of these here. An XBee breakout board is sold here. Jennic is on this site but they are low in my preferred vendor list due to the nature of the product and software.
RonnyM:
The Mirf2s have a carrier sense circuit. This detects ambient RF on the assigned frequency and can wait until it is clear to send. Using multiple transceivers, this helps keep data collisions from happening. It sounds like this is what you need. Range on 2.4 gig is more limited than 434, but these guys are neat. Right Brennan?
Ron
Yes, the MiRF-v2 boards (specifically the Nordic nRF24L01 chip that is on this breakout board) does indeed have a carrier detect (CD) signal, which can be polled by the micro to see if any 2.4 GHz devices are communicating in band. As RonnyM said, this is very useful when you are trying to operate a protocol in which multiple nodes can transmit at one time in order to avoid data collisions. To my knowledge, the nRF2401 chip that is on the board that you linked to (the original MiRF), does not have any type of carrier detect.
As far as the ZigBee modules that stevech mentioned, I have not used them so I can’t really offer any guidance with them. You may be able to benefit from the mesh routing, etc. that these chips offer.
If I were you I would probably weigh either buying the MiRF-v2 breakout or the ZigBee board. I would avoid the original MiRF and really the nRF2401 in general because it pales in comparison to its newer replacement, the nRF24L01 that is in the MiRF-v2 boards.
I’m using the XBee ZigBee modules now, and without going into the nitty gritty details, I have this to say: they work! I’m just a beginner dabbling with electronics, and the ease in implementing them on my circuit has been a great boost. I’m sure I will learn alot more the hard way through those 434MHz modules, but my project’s on a deadline and I need to move on.
Thanks for all of your suggestions, they have been really helpful.
Oh, and if anyone’s interested, the Arduino playground has this link on how to connect up the XBee: http://mrtof.danslchamp.org/AXIC
On another tangent: Yes, it’d be great if Sparkfun is allowed to sell the XBee modules. When will the XBee breakout boards be back in stock?
XBeePro modules worked well at 1 mile line of sight.
XBee modules are 1mW and of course less range.
I’m concerned that MaxStream’s adoption of Ember’s modules for 802.15.4 and ZigBee - called “XBee Series 2” means that they may drop the XBees which are based on Freescale’s chip.