I would agree with RichG, 100% accurate detection of a car passing the start/finish line is the most important point.
In my latest project (for a single lane rally track) I've used a 741 Op amp to compare the resistance in two LDRs mounted in the side of a bridge. One LDR is placed low down (where a car would cover it) and the other is placed well above nowhere near the car or track. On the other side of the bridge are two high powered white LEDs shining directly at the LDRs. When a car passes, the Op amp compares the difference and sends a signal to the output (this is where you need to think about the counting part of the project and what you need - I suggest you ask your Electronics teacher what is available). Some companies are able to supply complete counting kits as electronic projects for schools. I'm pretty sure but the exam board won't be expecting something to rival the best Scaley/Ninco/SCX can offer so don't over complicate it!
Good luck
Alan
In my latest project (for a single lane rally track) I've used a 741 Op amp to compare the resistance in two LDRs mounted in the side of a bridge. One LDR is placed low down (where a car would cover it) and the other is placed well above nowhere near the car or track. On the other side of the bridge are two high powered white LEDs shining directly at the LDRs. When a car passes, the Op amp compares the difference and sends a signal to the output (this is where you need to think about the counting part of the project and what you need - I suggest you ask your Electronics teacher what is available). Some companies are able to supply complete counting kits as electronic projects for schools. I'm pretty sure but the exam board won't be expecting something to rival the best Scaley/Ninco/SCX can offer so don't over complicate it!
Good luck
Alan
