hi I know what I want to achieve but not sure how to do it. I used to be really good at electronics at school but that was some time ago now and I fear I have forgotten more than I learned. I am building a model bus layout with a working vehicle. The vehicle has a magnet on the bottom and I have a reed switch under the road which activates an led every time it passes. What I want is a circuit that makes it so the light only comes on every 3rd or 4th time or even better on random passes. I have tried search engines but am that far out of it I dont know what type of circuit I am looking for. can anyone point me in the right direction?

 

To be clear, this is for a small, model vehicle and track, right?

How random are we talking? Should the number be between1 and 10,1 and 100, 1000?10000000?
If you don't mind a 2^n limit, a LFSR(Linear Feedback Shift Register) can do this.

Or you can go an easier route and slap a microcontroller on there...