XBee Pro RF Interference with X-Band?

Subject: XBee Pro RF Interference with X-Band?

Dear Sir,

I originally addressed the following email to Digi tech support. I've also called tech support at Parallax and got their suggestions. I've sent the email to Arduino tech support with the hope that my issue might not be too far out of bounds. I await Arduino's response. The suggestions I have gathered are included below. I will now see if the user community has any recommendations.

I've put together a motion detector using:
Arduion Uno, Arduino wireless SD shield, X-Band motion detector and a XBee Pro (XBP24-AWI-001 revC).

I initially assembled the detector on a breadboard and got the system to work most of the time. Early on, I had trouble positioning it near a plotter I have. For some reason, I my motion indicator led was flashing rapidly even when nothing was moving. By adjusting the detector's position I was able to stop the rapid flashing and could use the system effectively to detect motion. I call this unit the transmitter henceforth. It is important to note that the unit was working at this point.

I then assembled the transmitter on a PCB board and put it in a project box. From this point on, even after making another attempt on a breadboard, the rapid flashing returned permanently. No adjustment can get rid of it while the XBee is transmitting. I made certain I keep all sensitive devices away from the heat of my soldering iron. I made no changes to the transmitter's script.

The Arduino wireless SD shield has a USB/micro switch. When set to USB, the rapid flashing stopped and the tx led lit up on the shield. When set to micro, the rx led lit up and rapid flashing starts. I'm wondering if the 1, 2 & 3's I'm sending via Arduino script and the XBee is interfering with the X-Band unit.

I have focused in on the XBee by:

  1. Setting up the detector without the XBee and Arduino wireless SD
    shield. Using only the Arduino Uno, I was able to get a stable device, no rapid flashing.
  2. Using the Arduino Uno and the wireless shield, I got a stable device again regardless the
    USB/micro switch setting.
  3. Using the Arduino Uno, wireless shield and the XBee from my receiver unit, I got the rapid
    flashing again with the USB/micro switch set to micro. So it wasn't just the XBee I used in the
    transmitter that is causing the flashing, both XBee's give the same result.
    Conclusion: Something about having XBee in my system is interfering with X-Band detector.

While I was writing this email, I received a call from Digi tech support. The tech thought the XBee's RF signal could be interfering with the X-Band. He suggested putting a RF cage around the X-Band to see if it would stop the flashing. I cover the X-Band with several layers of aluminum foil to see if it would stop the flashing. It didn't. He suggested getting a wire mesh. I'll see if I can find some at the hardware store. He suggested removing RF induced line ripple with a filter capacitor. This suggestion has almost exceeded my knowledge and ability to attempt. There are three devices in this system that may require this potential fix. I don't know where to begin. Maybe putting it on the 5V power line from the Arduino to the X-Band might be tried. The X-Band has four pins: EN, OUT, 5V and GND. The OUT pin is the source of the detected motion. I just don't know what to do.

I'm finishing this email so I can address Arduino and Parallax (X-Band mfg) with this information. And I'm sending it to Digi tech support with the hope someone there might have some other suggestions.


P.S. I called Parallax and the tech didn’t have a specific solution for me but agreed there might be a RF interference problem that might be solved by placing a decoupler capacitor between the OUT of the X-Band and GND (setup a parallel circuit). He recommended getting capacitors with values between 0.2 and 1.0 microfarads from Radio Shack and finding out if any of them or a combination of them help. He’s suggesting the wire attached to the OUT of the X-Band may be acting as an antenna.

Hi Chirs,

I have just encountered with the problem you explained. Just wondering you can solve the problem now?