Seeking help for a 2 lane finish line for cub scouts cubmobi

[sporty]

Hello,

Im not very electronic smart. Thought someone could help me out.

I am a volunteer on a Cubmobile committee for CUb Scouts.

We have a Cubmobile race coming up.

However we need a finish line (winner)

its a 2 lane race, each lane 4 foot wide.

The 1st car to break the beam, would win, a light should turn on to announce the winner of the lane that one.

I found alot of stuff out there for Pine wood derby races. However, the components and so forth are different.

meaning since the beam has to travel 4 feet in day light and sun. compared to less than 1 foot for a PWD race.

I was hoping someone would be able to tell me what kind of IR diode or laser I should use and strength. and so forth.

Sporty

 

[viclick]

Re: Seeking help for a 2 lane finish line for cub scouts cub

Hi Sporty,

Nice thing to do - donating some time to kids. I had bad luck with IR in sunlight (I'm not "not very electronic smart" either) when trying to implement a sensor across my garage door. I did manage to get two Pulnix PS-30SE sensors to work though. I got them on eBay for about $35 a set (I think). Bright sunlight can blind an infrared sensor if it isn't compensated very well, even if it is modulated.

Lasers would be a good way to go but they require pretty precise alignment, and all that entails.

Ultrasonics would work very well. Parallax makes a nice unit (it's called the PING) that will work very well across four feet. Put a board across the lane to refelct the sound off of and you're in business. When there is no car, the distance across the lane is fixed. When a car passes, the distance changes. No alignment needed, no sunlight problems. One sensor might interfere with the other but that might not be a problem in just four feet (the beam spreads more the further something is away).

Another idea is to put a photo sensor on the ground pointing up. When a car passes over it, the amount of light it detects is much less which can be easily measured. Here you are also looking for a change - a dramatic decrease from ambient light. Some compensation may be needed for ambient light changes (a sunny day that turns cloudy, for example) but probably not. This is a very easy way of doing it.

Regardless of the detection mechanism used, the electronics will have to decide on the winner or a tie - you've probably already seen that in your pine derby research.

Good luck. Keep us posted. You can email directly if you like.

Vic