Sensor Ideas

Using Arduino Sensors
1

Well hello all. I'm am fairly new to the Arduino game, have been fiddling around with it for a few months in a class and now am trying to develop something useful with it all.

What I'm trying to do is alter a timing system for dog races (yes, dog races). The added challenge is that these are dog swimming races, so my sensors need to be waterproof as well. What needs done is the final "trip" at the end of the race. The dogs are still in the water at this point, so it's a big of a challenge, can't use the same trip laser used at the start of the race. Basically, I see three options.

1: An impact sensor as the dog hits the exit ramp on the water.

2: A motion detector rigged above the end point.

3: An underwater trip laser, if such a thing exists.

Each option has it's own set of challenges. The first one has to be waterproof, sensitive enough to detect small dogs, and tough enough to withstand hard impacts from big dogs. The second has to be able to able to have a very narrow field of view for consistent timing, and not over-sensitive to respond to waves in the water. The third, well honestly I don't even know if this is feasible/possible, couldn't find any info on underwater trip lasers after a bit of research.

Just curious as to all of your more experienced thoughts on all these options are, and am open to suggestions.

2

Perhaps a piezo element might be a place to start - waterproofing it might be tricky, but they respond well to impact especially if mounted on
slightly flexible material like a plastic sheet - perhaps epoxied on with epoxy covering the piezo disc and the connections to water proof it.

They are cheap and sensitivity is set by choosing the right resistor in parallel. Don't be confused by piezo beepers, you want a raw
piezo element like this: http://www.maplin.co.uk/piezo-transducers-3202

They are quite brittle, so make sure they are mounted to a stiff enough sheet. In the past I've used these loosely stuck onto the
side of a drum to pick up impacts - works well.

3

Thanks Mark, I'll give that a shot. Waterproofing will be a challenge as you mentioned and I'm a little unsure of where on my impact board I'd mount something like this, but with a bit of creativity I might be able to make this work. Any other ideas? I'm willing to spend a bit of cash on something that I am confident would work well and is reasonably priced.