Problem with U2270 and EM-40001 transponder

[volod_ua]

Hello.
I have a problem with U2270B and EM-4001 transporder.
Antena I have L=627uH. And build other shematic, work but I don`t have good card code.
In Em-4001 the first 9 - bits is 1, I have this bits but last bits is not good.
In pin U2270 - Output a have f = 0.4~2.4Hz when put card f = 1.54~1.65;
In coil f = 122.5Khz. Use 220nF and 1.5 nf for pin HIPASS,Input.
For decode I use AVR .
Can you help me.
volod_ua@yahoo.com

 

[wek]

u2270b output

> In Em-4001 the first 9 - bits is 1,
> I have this bits but last bits is not good.

I am not familiar with em4001. so just general questions, maybe some of them will give a clue.

How do you mean "not good"? Is it "all 1", "all 0", changing each time, or...?
Is the "first 9 bits = 1" a method of synchronising? If so, is the rest of code such that there is no 9 consecutive 1?
Try also to capture the raw output of U2270B on a digital oscilloscope (or logic analyser - the simplest will do) and do the "decoding" "by hand" - maybe your decoding fw is flawed...
Also try to tune the antenna circuit, if the transponder has a built-in antenna/oscillator circuit, it might be off the nominal frequency slightly (try from 115 to 135KHz)

wek

 

[volod_ua]

output u2270b

How freq must be in pin Output(U2270B) when transporder is not present

 

[wek]

u2270 output

This is a bad question. The U2270 effectively demodulates a very weak AM modulation of the 125kHz "carrier". When the transponder is not present, the output of U2270 is effectively noise, and the character of that noise depends on many factors present in the system and in the environment.

If you cannot get (borrow) a digital storage oscilloscope (DSO) or a logic analyser, you can try to sample the output from the U2270 into the AVR and then send it out in raw into PC (not attempting to decode it). That will give you clearer picture of what happens there.

wek

 

[volod_ua]

problem u2270b output

Maybe you can tell me program for analis data

 

[wek]

Help U2270

Do you mean Manchester decoding on AVR? Sorry I don't have any (using different type of modulation; but even if I would have Manchester, I couldn't give that away, and, anyway, it's not on AVR)...

I am trying to give you clues but obviously you have to work it out yourself.

wek

 

[BoardMan]

Re: Help U2270

I notice that at the output pins on U2270B there exist noise, which goes to detector diode and demodulates as random signal. I tried to fix that without luck. I think that the noise goes from the IC' output buffers or OSC block. I think that for some short period the outpus are switched off, when there is no transponder. When the transponder present then the amplitude of demodulated signal is much higher than the noise that comes from the output driver. Does anyone know some tips to remove that noise?

 

[wek]

Help U2270

You have to remove that noise in program, i.e. when decoding the Manchester or whatever modulation.

The U2270B is a very sensitive IC - the modulation on the carrier is really very small, even with good coupling between the "base" coil and transponder - so it is unavoidable to pick up some noise.

You might be able to decrease the sensitivity (I don't know I never needed to decrease it only to increase), but I don't think you will be able to get rid of the noise completely.

JW