Good point about simultaneous passing of cars, the track in question does
not have any gantry or bridge over the track unfortunately which will make
it difficult.

The way our timing operates is as follows:

The timing marker is placed about 1/2 way round the track. The car enters
the track from the pit area and has that 1/2 lap to warm up, on completion
of the session (4 laps), the car passes the beacon mid track and has 1/2 a
lap to cool down.

This has the fortunate benefit that we can place the beacon in the middle of
a corner mid track, rather than on the straight where passing would be more
prevalent. This would minimise the problems associated with cars passing on
the beacon, and this, coupled with the second method of detection using RF,
would mean that we wouldn't have much problem with missed cars.

Perhaps a tall beacon, pointing down at the track at 45 degrees or so, and
with a 'tall' IR swathe would paint the whole track and allow detection of
simultaneous cars?

-----Original Message-----
From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On
Behalf Of 0xDEADBEEF
Sent: Wednesday, 17 March 2004 12:48 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: Identifying cars

I can see a problem... what if two cars do pass the finish line nearly at
the
same time just with a difference of less than a car length? I tell you, no
IR
method from either the right or the lift side, or even both will work. You
need to detect a passing car from over or under the track!

So the easiest and cheapest solution that comes into my mind now is to place
a
frame on the finish line. this frame holds a set of IR diodes in place over
the track.
The cars will be equipped with IR recivers turned upwards and RF
transmitters
to send the ID signal. (the IR recivers must be placed at the front of all
cars, so they're all at the same place relative to the car, to be fair.)
When a car passes the frame and catches the IR signal it will send its ID
signal via RF. This signal can be catched up by a computer that does all the

needed calculations and processing. The RF ID circuit can be a cheap digital

circuit connected to a cheap RF transmitter module.

A more advanced and professional method would be to put RFID's under the
cars
and the reciver units under the track. The powering reciver units hafe to be

powered very low, to limit their range to the finish line. Everytime a car
passes the line its RFID get's powered by the reciver and sends its ID
signal
back. This ID signal gets a time stamp when recived and then you have all
needed data for processing...

MfG,
Do.Pe.

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