Dr Skip wrote:
> alan smith wrote:
>   
>>   I've sent an email to the end user asking to describe what isnt working exactly.  Of course I expect an answer...it doesnt activate when stepped on....hmmm...guess its broken.  I'd rather not make too many trips to site, waste of time and fuel (but I charge these guys mileage at least)
>>
>>   
>>     
> That's kinda why I suggested looking at failure modes. If it's wet, and
> muddy, there's lots of possibility for the pressure sensor not having
> anything to press against underneath as mud softens, if I understand the
> design right, and any design that depends on up/down motion will
> probably fail. Mud will get in the gap, cavities can form under the
> stone, grit can seize moving parts, etc. The design has to be able to
> return to the start position under all mud conditions most likely, so
> any motion has to be sealed. I would also guess the travel is small,
> since stepping on stones that move a lot would be annoying, and this
> makes the affect of grit or shifting worse.
>   

Yes. I imagine the problem to be ice crystals  over time breaking  the 
mechanism apart.  But it
needs to be researched carefully before choosing a workable method.

--Bob
> How about a light beam across each stone? The foot breaks the beam.
>
> Or embed a hall sensor or better, a reed switch, in the top of each
> stone and embed some rare earth magnets in the soles of the stone
> walker's shoes?
>
> If the step can be made loud enough, as in hard shoes vs sneakers, an
> embedded electret element might work too, but will have to be adjusted
> so thunderstorms and lawnmowers don't set it off. Same idea as the piezo
> one, but more easily waterproofed I'd think.
>
> -Skip
>
>   

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