Debbie wrote: > --- peter green wrote: > > >> what are you using theese counts for? >> > > Sounds like they want to check up on ticket sales vs cars in/cars out. > > >> do in cars and out cars take different routes? >> > > Yep. > > >> what accuracy do you need (e.g. what proportion of counts can you afford to >> gain/lose before the data becomes useless to you) >> > > Basically, want to log all cars. The vehicles will be pretty close to the > sensor and slow moving (<15 k/h) so should give big magnetic sig? Path width > should be, say, <5metres. It's a sports event - as the car park fills up, they > move the poles, path and traffic wardens someplace else. Ditto car counter. So > you probly don't want a gizmo that needs turf dug up or dangles loops or is > fiddly to align. I'm thinking magnetic would be the way to go? Those Honeywell > sensors have analogue o/p but that wouldn't be a big drama. > Thanks -Debbie > > > > ____________________________________________________ > On Yahoo!7 > Answers: Share what you know and you might make someone's day > http://www.yahoo7.com.au/answers > The system I was familiar with used a loop buried in the concrete. The loop (plus the concrete) formed a tuned circuit. When a car drove over it, it detuned it because of the metal of the car. It was rugged and durable. Very easy to design, too, and insensitive to people and small objects over it. About 2m in diameter, buried about 4" deep. About 100 turns of #24 magnet wire. Very similar to the familiar "metal detector" design, where a loop of wire, covered with a lead foil shield, was embedded into a plastic wheel. You have to have the shield to stop capacitive (leaving only the inductive) effects. These are used in airport parking lots to dispense a ticket when a car drives up, as well as to verify that the car has left the dispenser. --Bob -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist