Robert,

Thanks for the reply. I took a coil off a working EM4001 transponder, and
assumed that the Q would be good enough. I also fitted as close to a 74pf
cap as I could get in parrallel with the coil. A parrallel resonance cap of=

this value is integrated into the EM4001 chip. I have also got quite a
powerful tag reader that reads normal tags at a distance of 10cm
comfortably.

The carrier modulation frequency is the common 125khz. The bit rate is 64
times the carrier frequency. The EM4001 chip uses the carrier frequency as
its clockin. I have not done this. I just tried to time things as close as
possible with nops. Is this most likely where my problem lies in your
opinion and would the input of the pic be able to detect this timing signal=

alright?

I don't have an oscilloscope at the moment so I'm working in the dark.

Jason

-----Original Message-----
From: Robert Rolf [mailto:robert.rolf@UALBERTA.CA]
Sent: Thursday, February 27, 2003 19:08
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: how do I emulate a rfid tag on a PIC12c508


What is the Q of your coil? It is probably not high enough so the
reradiated field strength is insufficient. You said nothing about a
tank capacitor so that may be your problem. The reader sees
no reflected energy so it has nothing to 'lock' to. An open coil does
not 'couple'.
Is the modulation depth what the reader is expecting?
Does the EM4001 use frequency division? e.g. 500khz carrier?
If so, your modulation must be synchronous with the divided carrier.

Have you eavesdropped on a 'real' device to see what the field
densities and modulation look like?

Robert

Jason Dini wrote:
>
> Does anybody have experience with pic-based tag readers. I am trying to
use
> a pic to emulate an EM4001 tag (125khz, manchester encoding, amplitude
shift
> keying, 64 bit ) for data logging purpose. I have connected a coil betwee=
n
2
> pins and I am modulating according to specification to cause the required=

> "back scatter" but I am having no luck. Can anybody suggest anything or
head
> me in the right direction?
>
> Thanks
> Jason Dini
>
> Jason Dini
> tel: (021)915 6505
> SOUTH AFRICA
> mailto:dinij@orchid-sa.co.za
>

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