View Full Version : RFID Help Needed

07-22-2006, 04:09 AM
I am having problems with the Parallax RFID reader (with
the 2 inch buttons) using a Stamp2p. The reader will read the
tags but the reading distance is highly inconsistent. I suspect,
the code, the operator, or the test set-up
The Code
enable pin 1
sout pin 0
T2400 con 1021
idx var byte
chkChar var btye

low enable
serin 0, T2400, [Wait($0A), SPSTR10)]
high enable
For idx = 0 to 9
Get idx, chkChar
Debug chkChar
Debug Cr

the Operator
started with a BS1 in 1994, a BS2 in 1996, been away a looong time

the set-up
The tag is set up vertically leaning against a wood block
and the reader approaches slowly with the faces parallel.

the result: sometimes consistent readings are achieved at 3 inches
sometimes readings are not achieved until less than 1 inch
sometimes the reader has to be waved back and forth for a few minutes

With the setup rotated so that tag and reader are horizontal, the tag
is never read until within one inch of one another.

Using a power supply, the reader is using 5 volts and about 110 ma.

I'd appreciate some suggestions on how to achieve consistent results.



John R.
07-27-2006, 08:32 PM

I've seen some of the same inconsistancy, and have been working on some "controlled" testing. I've had to put the project aside, but will bring it back out and get you some quick findings. My "preliminary" playing around showed things more consistant than they first appeard, but I was using some 12mm "capsules". I've got some of the round tags, and I'll give those a try, possibly tonight, or over the weekend at the latest.

I'm using a BS2 off a wall wart for power.

John R.

8 + 8 = 10

John R.
07-30-2006, 06:16 AM

I've got the RFID module back up. Using the round "World Tags" I get the following response very consistantly. My reader is fixed, and I move the tags. I was holding the tags by my finger tips, and also got the same results when "folding" my fingers over my palm with the tag inbetween. Having the reader horizontal or vertical didn't make a difference. My reader is also in "free air" with nothing behind it.

With the face of the tag parallel with the reader, approaching "on center", I get a reading on all 5 of my tags between 2.5 and 2.0 inches. This holds true as long as the "center" of the tag remains within the boundries of the antenna. Once the center of the tag is outside the boundaries of the antenna, I need to get within 1" or closer. It doesn't take much past the center to get a very rapid fall off in response. The antenna acts very "directional". This distance holds true for me when approaching perpendicular to the plane of the antenna as well as when "swiping" the tag parallel with the antenna.

When holding the face of the tag perpendicular to the plane of the antenna I get a reading when the center of the tag (not the leading edge, but the center) is between 2.0 and 1.5 inches. Note that there are some "gotchas" with this orientation. If you approach from "perpendicular" to the antenna, and are "on center" reading is very inconsistant. I almost suspect that if I had a smaller tag, I might be able to pass right through the antenna. Once I get a bit "off center" all is well again. When the axis of motion is parallel to the plane of the antenna, response is very constistant at 1.5 inches from the face of the antenna to the center of the tag. Response at 2" is spotty.

Most of my work has been from the face of the antenna opposite the components, but a few tests from the component side show similar results.

I've attached my code. I have a BS2, and am using a Parallax serial LCD for the readout. I'm only displaying the last four digits of the tag, and let the display just "overwrite" itself. I really should work on the spacing, as it just burps out 5 characters (4 for the tag, and one space) and the dispaly has 16 chars...

I hope this helps, and would be willing to do more testing and sharing of results. In addition to the World TAGs, I also have 0.5 buttons and 12mm "capsules".

John R.

8 + 8 = 10