Communication between two XBees - very basic!

Hi all,

Firstly, I’d like to say that I’m a CONSUMATE ANALPHABET in electronics!

My problem: connect a ship equipment called AIS (Automatic Identification System) to a remote PC. This is a mandatory equipment that transmits ship’s data by VHF; data is output by a COM port, by default set to 38400/8/N/1. No problem to connect directly.

After reading about the XBee, I wished to try it. I bought two modules from SparkFun and two Explorer boards: one USB, which I intend to leave at the PC side, and a serial, intended to the receiver side.

My very basic doubt: one module is 900MHz (XBee Pro 900 RPSMA) and the other is 2.4 GHz (XBee Pro 60mW Chip Antenna). Do they communicate? If so, how should I configure them - I read about routers, endpoints etc and I’m a bit confused… they are still packed.

Thanks in advance and excuse me for taking your time with so basic stuff.

The 900 MHz module will NOT communicate with the 2.4 GHz module. Only modules of a similar type can “talk” with each other over the air.

As far as which type of RF module to use, how far from the Remote PC is the AIS? What sort of RF path exists between these two points? What type of traffic will be going across this wireless RF link, assuming a path exists?

Thanks very much to your reply! Fortunately I’ll travel soon to the US, so I’ll be able to get the matching modules.

For this project, the receiver will be on top of a silo, about 150m straight line from the PC. Can’t be line of sight, some walls lie between. There are some administrative PC along the way, not involved with the traffic monitoring, so I wonder if a Xbee module could be left on them if needed or even a wall router, if the signal is not strong enough.

The traffic varies a lot, but I prefer to deal with a continuous flow. This is due to the AIS specs. If several vessels are around at high speed, they update their info at maybe 3s interval; moored vessels, at 30min; vessels carrying dangerous cargo may be polled every second. The protocol they use is self organizing TDMA - one transmits and reserves the next slot. AIS hardware defaults to 38400 8 N 1 and some is even fixed on these parameters, so I’d like to leave like this.

There are some situations where I simply want to avoid cabling or I want a simple setup for demonstrations, with receiver and PC at the same room or at the next door. For these cases, I have a Roving Networks’ Bluetooth stick with a DB9 connector that I leave at the receiver and it talks nicely to the notebook’s Bluetooth at short range.

More ambitious projects in the future could deal with AIS repeaters and radars at long distances, like 10-20 miles range. For those, what about the XTend RF modems?

Thanks in advance.

I wonder if the best bet - not only for this project, but also for on site demonstrations - wouldn’t be the iDigi™ X4 Starter Kit ZB.

At $149, I’d get a gateway, a wall router and another module. With the gateway I can integrate all the modules, even if they are of different features, right?

On the PC side, the traffic monitoring software allows me to choose where to read from: a COM port, file based, TCP port etc. I can point it to the gateway. I suppose that the NMEA strings output by the serial port of the receiver are being broadcasted by the XBee attached to it, received by the gateway and made available at its Ethernet port, am I sure?

You would need a python app to facilitate the communication between the RS232 adapter attached to your receiver and your application. Since your app allows use of TCP ports, the TCP Sockets script might do the trick: