Hi, wonder if anyone can help/point me in the right direction.
I've built a rfid reader using the atmel u2270b front end chip, after a lot of poking about I've got it to reliably read fdx-b protocal animal tags. (I can now identify my sheep!) I bought the iso 11784/5 standards and unfortunatly the rfid tags I have for my cattle are of the hdx type. In the standards it states that the activation field should be turned off to enable the hdx tags to respond, they charge a capacitor then transmit. I've programmed the pic to turn the field on and off via the u2270b and using my cheap scope can see the response of the hdx tag. The signal is taken via a diode to a capacitor divider then to the input of the atmel. I tried putting a op amp in to amplify the hdx signal and was hoping to use a pic with on board comparators to read the signal (which uses fsk). Unfortunatly for me this is where my knowledge lets me down, I've no formal electronics education and have taught myself as I work on stuff like this, so there are quite big gaps in what I know. When the op amp is conected the reader will no longer read fdx-b tags, I guess the modulation of the field is a small signal and gets drained off? I was hoping I could use a transistor to switch the signal to the op amp after the field is deactivated? The pic could switch the transistor at the same time as the field, my question realy is what type of transistor do I need? The field is turned on by a high output from the pic. Sorry for the rambling post.
Thanks Geoff

 

Hello,

Can you post a schematic of what you have upto now?

Bertus

 

Hopefully there should be a very basic pdf attached, if I connect the scope across the coil I can see the field start and stop, if I hold a hdx tag next to the coil I can see its response, unfortunatly my scope won't let me zoom in on the tags signal, using the trigger function it starts when the field does. I'm not sure I have the op-amp correctly connected, I found a few pages on the net about rfid and the op-amp is set as a band pass filter? I dont know what that is but was hoping I could isolate the tags signal. However when I connect its input to the u2270b's input the reader will no longer read the fdx-b tag. On a side note, what software do people recomend for drawing schematics?
Thanks Geoff

 

Been pluging away at this, I've now put a 2907 transistor in my circuit, its collector is connected to the input of u2270b, and base via a resitor to the pin of the pic thats turning the field on and off, I've read up a bit on op amps and set it as a negative feedback amp, however the problem I have now is the output from my pic isnt a square wave as I would expect. The pic is a 16f818 and i'm using portb,3 as my output. This affects the signal the op amp is reciving. On the plus side the fdx-b part is still working. Any suggestions would be welcome.
Thanks Geoff

 

Hello,

Do you have a datasheet or a link to the datasheet of this u2270b ?
I want to have a look at the specs of this.

Bertus

 

Hopefully the data sheet should be attached.
Thanks for looking, Geoff

 

Hello,

Is the system not sensitive enough?
The standard fequency is 125 kHz.
This could be the case if the frequency of the 2270 is not correctly adjusted.

With the resistor on the RF pin the frequency can be fine-tuned.

Bertus

 

Have just been looking at my circuit, wonder if I'm going about it the wrong way? The signal from the HDX transponder is very small, I can see it across the coil but by the time its been trough the capacitor divider its all but gone? Someone suggested using a PIN diode to connect a op amp to the coil after the field has been turned off, knowing very little about PIN diodes I've looked up a bit of info, unless I've missunderstood it I would have to put 80-90v on the diode to turn it off? The voltage on the coil is around 80v when its active, the signal about 5mv! Alternativly is there a op amp that wont be cooked by 80v, the pic knows when to try and read the signal.
Thanks Geoff

 

Hi, the chip works fine to read the fdx transponder which as I understand modulates the activation field. The hdx transponder transmits after the field has decayed, the 2270 wont output this signal. However I can see the signal across the coil, its this signal I want to amplify. (I think!)
Thanks

 

in response to your question about schematic editors, I like using Eagle. it's free and has a fairly large library available out on the interwebs.

 

Thanks, had a quick look but didn't look very free! As regards reading the HDX transponder, I think I was making my life to difficult?! I now have a working circiut to read both types. I used the tms3705 from texas to read the hdx and the u2270b to read the fdx.

 

http://www.cadsoftusa.com/downloads/freeware/ <-- this explains it, there are paid versions, the limitations of the free version are only noticeable to me in the PCB editor (size limit 4x4 or something).

 

Thanks, had a quick look but didn't look very free! As regards reading the HDX transponder, I think I was making my life to difficult?! I now have a working circiut to read both types. I used the tms3705 from texas to read the hdx and the u2270b to read the fdx.

Hi Geoff - I've been trying to make an animal rfid chip reader using tms3705, to identify neighbourhood cats at our catflap. It returns the diagnostic byte indicating that all is well but I never get any data. I know this is a long time ago, but do you have any firmware you could share?

Thanks - Philip

 

Hi,
The only stuff I have is a mpasm sci reception routine, but I guess if your getting the diagnostic byte you've cracked that bit?
I've a feeling most of the implanted animal transponders here in the UK are fdx-b which the tms3705 won't pick up.
Where about are you? The best thing would be get a hdx transponder so your starting with something you know should work?
Good luck , Geoff

 

Hi Geoff -

Thanks for the quick reply! I'm in UK too - Herts.

I started off with a 125KHz reader RDM6300 - quite cheap on eBay - as I read somewhere that at a pinch it might read 134KHz. It contains an LM358 dual op amp and a 20 pin QFP chip marked SIL F330 which looks like it may be an 8051 clone. I also got a bunch of EM4100 tags which it reads.But it didn't work on a friend's cat.

So I went for the TMS3705. But when that didn't work (beyond the diagnostic byte) on the friend's cat I got some 134KHz tags on eBay advertised as clones of the tags you test a microchip-enabled cat flap with. But it didn't read them either. But the RDM6300 did! The TMS3705 doesn't work either on a credit/debit card, a passport or a Herts County library book.

It looks like you're right - the TMS3705 is hdx but it seems the RDM6300 and all the tags I have are fdx.

What would you suggest for a cat reader? It seems the u2270b may be end of life though it looks like I could get one for around a fiver from China. It'd be nice if I could hack the RDM6300 but I'd probably first have to hack some form of 8051 programmer. And are there any cheap hdx tags I could get hold of just to check I was driving the TMS3705 correctly?

Best regards - Philip

 

I used the u2270b for a bit until it was going end of production, farnell still have some for just over £3, the other alternative is the em4095.

Have you got a scope ? If your going to do much RFID you need one, you can check the field is being activated then?

If you can wait a bit I've nearly finished my latest RFID reader and was considering selling some module's, would be on a UART interface.

Cheers Geoff

 

It looks like my RDM6300 ought to do the biz but for some reason its sensitivity seems to have plummeted since I first tried it, only detecting a tag if it's within the coil and at a specific angle. That may be why it didn't work on a real cat. If not I might get an EM4095. I threw out my 45 year old Telequipment 3MHz scope a couple of years ago (but saved the valves to flog on eBay) after getting a cheap Chinese £20 1Msps DSO which takes up a tiny fraction of the desk space. It can see the RF in the coil but isn't really up to debugging - hopefully that wouldn't be necessary to follow a reference design.

I'll be interested to hear when you have your modules for sale (do you have a website you'll be advertising them on?), but to be honest I wouldn't be up for spending much more than a few quid.

Regards - Philip