wireless 125khz tag reader question

Hello rob,

I made a Manchester decoder with a U2270B and an AT89C2051 a while ago and if I can remember correctly, the decoding algorithm given in the TEMIC applications book was all I needed. There's no need for any other hardware. The OUTPUT pin of the U2270 goes directly to a uC port pin.

Since the bit stream repeats itself, all you have to do is start somewhere, count and store 64 bits and then look for the preamble byte (we use EM400x compatible transponder chips, so it may have been something other than E6). You've now found the beginning of your circular buffer and can now decode the rest.

I found the U2270 quite prone to noise and the output is always wiggling, even if there's no tag anywhere near it. The other thing is that the self-check resources of the 400x transponders boil down to a few parity bits, so this, coupled with the noisy U2270 resulted in loads of false reads. This should be even worse with the 5530, which doesn't even have those parity bits.

Good luck,

Viktor

somewhere,

E6).

Done the same with a pic. I made sure the header pattern (i used 0x7e) never reappears by encoding a 0bit after five successive 1bits. Hmmm, or something like that. I've got code somewhere if you want a look.

Noise hint, do not use tantalums for decoupling purposes on 125kHz RFID systems. For some reasons, tant's act like a nice bandpass filter for frequencies around 125kHz. It also helps by throwing a CRC into your tag data, that way you can do 1 or 2 bits of error correcting.

Hi there. Thanks for the replys. Is there anywhere on the net that I can get a copy of this TEMIC applications book. Cheers Rob

applications

Probably not anymore. However, try ATMEL as they have purchased Temic. You may find the old temic stuff in a revised atmel format.

Just had a look at the Atmel site and the U2270 docs are there. Have another go and if you still can't locate them drop me a mail.

You

Hi there. I have the datasheets for the u2270 and the 5530 , but they don't give decoding info. I have found another applicastion note however " Electronic emmobilizers for the automotive industry" which seems to have some info on this. Now all I have to do is figure out what the hell they are talking about :0) Thanks for the help guys!! Rob

What micro are you using? I have some code to read temic tags for a pic12c509. You can have it if you want it. It can be adapted to other pics if need be.

I am using an 89c4051 micro.

Hi to all again. I have picked up something odd while doing a bit of research on manchester decoding. The more sources that I look at the more discrepencies I find. Every second article gives me a different answer. Some say that a logic one is sent as a 1 to 0 transition and the others say 0 to 1. Here are just 2 examples:

decoding.

Since it's not defined anywhere, it's up to you, pick the one you prefer. The principle stays the same.

Michael

manchester decoding.

second

as

I only recently came across this thread--I've been playing with a similar setup--trying to read the data from an Atmel u2270b. I'm feeding the data output into the inputcapture pin of a BasicX system, and I'm defintely not getting what I'm expecting. I'm getting all sorts of odd-duration pulses, even with no tag nearby. Does anyone know what the u2270b should be putting out when there are no tags present? My reader circuit is probably suspect too, as I'm not exactly an electronics expert, and based it off of an example in the Atmel docs. If anyone can give an example of the proper way to hook this baby up, I'd appreciate it. Rob--you said you had a working reader circuit--any chance you'd be willing to share it? Thanks, Bob.

"Bob Stegmann" wrote in news: snipped-for-privacy@corp.supernews.com:

Hi there. I would give the design / diag to you , but my boss may have something to say about that.It is based predominantly on the design in the data sheet, the one for close coupling. If you build that you should be able to get a working cct. Range is not great , about 2 to 3 cm , but that is good enough for our app. I also had lots of noise at the output of the u2270b even when there was no tag present. This seems to be a problem with the u2270b chip. I did find that if you use a 1n4004 instead if the 1n4148 as detector as in the datasheet diag it improves things a lot.Have no idea why. Maybe someone can shed some light on this!! Maybe it is a capacitance issue. If you are still struggling give me a shout and I'll see if I can help. You can get me at snipped-for-privacy@yahoo.com Obviously remove the nospam. Cheers Rob

i am thinking of building a system like this but i want a range of about 1.5 metres whats the chance of this?

Tim

I don't think that it is possible with this system (U2270 & 5530 tag) to get 1.5m range. Well it certainly would not be easy. If you DO succeed, give me a shout and tell me how :0) There are a lot of devices well suited to that sort of "range" , but they tend to be self powered. I think they work at around 13Mhz( not sure if this is fixed) if I remember correctly. cheers Rob

snipped-for-privacy@orange.net (Tim) wrote in news: snipped-for-privacy@posting.google.com:

A lot of companies make 1-2m readers with 125kHz technology. A rule of thumb is that the antenna diameter is equal to the range. You can also increase the coupling factor by making the transponders larger (use a transponder chip and wind your own coil to make frisbee-sized tags). Driving a 1,5m antenna can be quite a challenge, though. The more power you put into the antenna, the harder it will be to extract the returned signal. I've never actually seen one of those big antenna systems and I'd be curious to know if they use just one coil or two: one for generating the field, the other for reading the tags.

Viktor

I don't think you will get that sort of range with the tk5530 tag chip though. The chip is only 11mm x 2mm x 4mm. If you were able to couple enough energy to the chip at 1.5m I doubt it would be able to dampen the field enough to detect with any sort of ease. Of course you could probably enclose said tag chip in a larger coil and couple enough energy that way....who knows. Cheers Rob