RFID reader affected by things against it's backside?

W9GFO

Due to space constraints, if I want to include an RFID reader inside my project box (I do), it will have to be mounted such that the battery pack is sitting right on top of it. The RFID reader is flat against the bottom of the box and the battery pack is on top of the reader. The box is plastic so the tags would be read by passing the tags under the box.

Should I expect any degradation in performance with the batteries so close to the reader?

Rich H

Mike Green

Yes, but how much is hard to say.

RFID readers, in general, work by generating a pulse of RF energy that is picked up by the tag, rectified to power the tag, then the tag transmits its information back to the reader using the power provided by the original pulse from the reader.

Batteries are made of conductive material and will absorb and dissipate some of the energy from the RFID reader and reduce the range of the RFID tag.

Since the RFID reader is mounted on the active surface of the box and the tag presumably will be passed very close to this surface, you may be ok since the range is very short, but don't expect anything like the range you'd get if the battery pack were not there.

W9GFO

The tag-reading range turned out to be better than I expected. The tags are being read reliably when within 2.5 inches (precisely) of the back of the box. The tags can also be read if placed on (or swiped by) the front of the box.

In the first picture you can see the RFID reader at the bottom right. It is underneath a six cell battery pack and the Gadget Gangster Propeller Platform. At the upper left is a socket for an XBee Pro.

The second picture shows the underside of the lid. It has a Parallax 4 x 20 serial LCD, it had to be cut to make clearance for the battery pack. To the right of it is home made pcb which holds the analog joystick(with push button) and above it is a GPS. Just out of view in the upper left is another push button. Then, on the left side of the box is the power switch, charging jack and a potentiometer. The side furthest from the camera has an IR led and IR receiver.

The last picture shows one of the robots that this box is intended to control. You can just make out the holes for the IR led and receiver on top, and to the upper left of the screen you can see where the five leds are mounted for the XBee.

Rich H