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[aprssig] APRS RFID reader?

Patrick winston at winston1.net
Mon Feb 1 23:09:01 UTC 2010


The system I have uses dual frequency tags made by IPICO, has two read 
antennas each of which is 1 x 2m, and reads a bubble around 20cm beyond 
and above the mat.  That said it will also read up to around 100 tags at 
a time so is also a little overkill for this purpose.  Regardless of the 
system, at least with passive tags, the faster tags are moving the less 
likely they are to be read simply because it takes time to charge them 
so they can fire their id.

Diode-oring the readers is unlikely to be reliable because you will run 
into situations when the tag will be in between to readers and they will 
both be reading... In my experiments its actually more likely as you 
increase the number of readers because the power providing fields will 
work together.

p

Robert Bruninga wrote:
>> The setup I have for race results is self contained 
>> with ethernet and usb to computer.. I find around 
>> 90% read  success of runners passing through the 
>> read area.
>>     
>
> What is that read area?  With say a reliable 6 inch read range,
> I would think that for a 3 foot wide door mat, one would need
> about 6 separate readers probably spaced a foot apart in two
> rows.  Each of these I assume has its own "reader" electronics
> which really drives up the cost from one $30 reader, to 6.  I
> wonder if we can just diode-OR the 9600 baud outputs.  Seems
> only ONE would make a detection at the same instant.  Especially
> if we spread them out in the direciton of the walker...
>
> I have updated my web page www.aprs.org/aprs-rfid.html to show
> the new APRS boots idea...
>
> Bob, WB4APR
>   
>>> Robert Bruninga wrote:
>>>       
>>>> I still think APRS-RFID... Is a next thing for APRS
>>>> experimenting
>>>>
>>>> Every ham hat could have a $2 chip in it.
>>>>
>>>> Then we can tell who enters the clubhouse or EOC... (it
>>>>         
> gets
>   
>>>> converted to APRS...)
>>>> See http://www.aprs.org/aprs-rfid.html
>>>>
>>>> Problem is, the maximum range reader I can find is only
>>>>         
> good for
>   
>>>> 10 inches max and it costs about $24:
>>>>
>>>>         
> http://www.sparkfun.com/datasheets/Sensors/ID-12-Datasheet.pdf
>   
>>>> It has provisions for a  wind your own antenna but still
>>>>         
> can
>   
>>>> only get to about 10 " (25cm).  But since hams are RF
>>>> experimenters, it would seem that we could improve on this.
>>>>         
> One
>   
>>>> sentence in the limited docs says that there has to be
>>>>         
> enough
>   
>>>> energy to activate the chip.  This implies to me that the
>>>>         
> limit
>   
>>>> is on the energy transmitted to the chip, not necessarily
>>>>         
> the
>   
>>>> read range.  Frequency is 125 KHz.
>>>>
>>>> To get reliable coverage for people walking through a door,
>>>>         
> I
>   
>>>> think we need about 48" range...
>>>>
>>>> Does anyone want to fill us in on the details?  I assume a
>>>>         
> 125
>   
>>>> KHz carrier in the antenna coil provides the energy for the
>>>>         
> RFID
>   
>>>> chip (this can be scaled up... Just needs more power)...
>>>>         
> But
>   
>>>> then I guess it has some off cycles so the chip can send
>>>>         
> back
>   
>>>> the 32 bit code?
>>>>
>>>> Bob, WB4APR
>>>>
>>>>
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>>>>
>>>>
>>>>         
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>>
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>
>
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