Setup two unicast Xbee Pro pkg pairs, having communication drops

Question

Hello,

I have a total of 4 Xbee pro serial modems which need to transmit two separate sensor data streams to a single computer. The pairs will receive for a while, say 15-20 mins then one drops communication. After a few hours the other loses communication. If I reset both transmitters, then coms resume. What can I do to ensure a constant link?

Here are some additional details about the setup:
The sensors are SBG IMU's transmitting various packets at 115200 baud with a nearly continuous data stream. I've set the modems to unicast, meaning the MY and DL are switch between the pairs. I've also set the channels to be on opposite ends of the spectrum, one pair set to CH C, the other set to CH 17. The PAN id's are also different between the pairs. The power settings are set to minimum. The radios are setup inside a lab 40x20ft and the transmitters are spaced about 5 ft apart.

Thanks,

Ed

Answer 1

May be your issue has nothing to do with interference between network and you are pushing modules beyond their limits.

Turn down one network and observe if the issue persist. In that case, you need to trim down on data transmission end or use hardware flow control.

Answer 2

You appear to be running with the 802.15.4 XBee radios at a 115.2kbps data rate and streaming limit.

There are a few things you need to know about this product and that rate.

First, due to clock divisors at the 115.2kbps data rate, the closest rate that the module is able to achieve is 112kbps or 111,111bps. While this rate is within the nominal rate of 115.2kbps, it is on the lower side of the tolerance. If your devices connected to the radio is on the high side of the tolerance, a baud rate mismatch can occur. To help address that, either open the COM port up at 112kbps or use two stop bits instead of 1. The extra bit slows down the communications just enough to address the tolerance issues. With the information you have provided, I suspect making this adjustment will resolve the issue.

Second, the 802.15.4 XBee have a streaming limit of 80kbps with the ability to support data bursts of up to 115.2kbps. You most likely will need to use hardware flow control to keep from over running the buffers.

Answer 3

These are great suggestions. I'll cut the data rates down and report back.

Thanks,

Ed

Answer 4

Folks,

Thanks for the suggestions. I think you've fixed my com problems.

Ed