Simple i/o sensor to detect contact/touch

Hi all,

Basically I am trying to build a slot car race track with an arduino with some modifications. I have a timer and I want the time to print when the "car" reaches the finish line. The "cars" will be traveling at extremely slow speeds and only weigh a few ounces.

I am looking for a simple sensor that sends a signal to the arduino when said sensor is touched; so when the "car" crosses the finish line. In theory I think that I can use a force sensor but I really don't want the analog values and feel that the varying numbers could cause more issues then needed because this will be moved a lot. So is there some conductive pad or other preferably inexpensive sensor that could be like an on/off (touched/not) value that can be passed through? Note again that the weight applied will only be a few ounces.

Thanks for any help! Been rattling this around for a while and want to open it up for more solutions

I would use an IR beam for the cars to break. Or a reflective optical sensor under the track pointing up through a hole.

As they said an IR beam, out them down a tube at each end as you want as narrow a beam as possible. Place the IR emitters on the bottom and the receivers above the track. There are piles of pinewood derby setups that use this method.

Thanks for the replys. I was hoping not to buy 4 IR sensors, one for each track. I've seen the slot car setup that uses a photocell under the track that triggers when there is less light(car over it at end). I think I've decided on making a contact switch out of two close pieces of copper that connects the circuit when the weight of the car touches them. Freeish and easy. Just have to work to get the connection to be reliable. If anyone has other suggestions please post them!

The problem with copper is that it will oxidise forming an insulating layer. Aluminum foil is better but connecting to it is tricky. The other problem with foil is the restoring force is not always sufficent to open the contacts when the car is gone.

An other option is to use a coil or hall effect sensor to sense the car through the track.