[chbot] OT RFID tags

[Andrew Errington]

On Wed, 26 Oct 2011 10:26:57 Marshland Engineering wrote:
> I can't seem to make any headway with finding a solution to our problem. It
> is for lap timing for motorcycle racing. There are many 'passive solutions'
> out there but they fall into the same category as the evaluation one I have
> on test. It doesn't work over a wide track!!.Active tags overcome this
> problem but I can't seem to find the supplier of tags and readers only
> sales companies who have very little real info on the systems. Anyone know
> much about this ?  There are many "suppliers" in the $8000 range but I'm
> looking for a low cost tag and reader.
>
> Cheers Wallace

My first thought is OCR.  Large, high-contrast, reflective tags (QR Code?  
Barcode?  OCR font?  A small set of unique colours?), lots of light, and a 
fast shutter speed to catch the image/images in the field of view quickly.  
You don't need a fast decoder, just a fast capture.  You can decode almost at 
leisure (in computing terms).  In fact, once the image has been snapped a 
human could take a few seconds to decode the tag, and the timing information 
is in the snapshot timestamp.  It's probably not enough to have one camera, 
you might need several across the timing line, but with a fixed mount you 
could set them up quite accurately.

Another option might be IR light.  Have an IR light 'curtain' across the track 
on the timing line.  Modulate the IR beam at a known frequency.  On the 
motorbike have a tuned circuit that is triggered by this frequency, and a 
sensor at a fixed position on each bike.  When the bike sensor detects the 
curtain have it send data by some means (radio?  IR?) with a message 
indicating "I was triggered x ms ago.".  Repeat the message many times and 
recalculate x every time.  By knowing x and the latency of the system you 
could accurately derive the trigger time.  Or you could have a high-accuracy 
clock on the bike (GPS-based?) to record the actual trigger time.

Or figure out how the $8000 guys do it and copy it.  I have no experience of 
motorbike racing but I do know that RFID tags are finicky, and they are 
difficult to 'fix' in free space, i.e. the timing line would be more like 
a 'timing cloud'.

Good luck- sounds like fun!

Andrew