Interlink makes force sensing resistors whose resistance
changes from megaohms to low hundreds of oohms when loaded with 50#.
About 0.2mm thick and 20 mm diameter. No perceptible motion.
Only problem is creep when under constant load (10's of minutes,
100's of ohms).

For binary sensing as you desire, should not be a problem.
Interface is an op amp to linearize, or comparater/schmidt
if you don't care about linearity. We use them in shoe liners
to control a medical stimulator. Biggest problem we have
is flexure failure due to sole flex (printed ink on mylar
cracks with repeated flexing).

You might also want to look at pain old membrane key switches.
They are available in singles. It's just a matter of devising
a suitable panel geometry to focus the force onto the actuation
area.

And your $50 package will sell for how much?

Robert

Rick Luddy wrote:
>
> I'm working on a project to build a dance pad for video games.  It needs
> four sensors, each one detecting whether or not an 11"x11" panel has
> someone standing on it.  The end result will look similar to:
> http://www.angelfire.com/d20/ddrhomepad/ddrpad1.html
> , although I plan to implement it differently.
>
> Most similar projects (including the example above) work by sandwiching
> some non-conductive foam between two conductive panels, detecting when
> the two panels touch.  For both durability and comfort, I want there to
> be no humanly-noticeable displacement when a panel is triggered.  I'm
> having trouble finding a type of sensor that can accomplish this.
>
> Each sensor needs to be durable enough to survive being repeatedly
> stomped on while also being able to quickly (within ~1ms) detect contact
> or release.  Each needs to be able to detect both sharp (milliseconds)
> and gradual (several seconds) contact and release.  Each must detect
> contacts  anywhere from a couple pounds of force up to hundreds.  Each
> has to be able to work no matter what causes the contact, anything from
> an elbow to a heavy rubber boot.  Each also needs to be able to detect
> prolonged contact anywhere from milliseconds to [at least] 20 seconds.
> All of this with a maximum low-volume cost of $2-5USD per sensor.
>
> Another requirement is that after initial testing, it shouldn't need any
> manual calibration.  If it needs to self-calibrate, it should be able to
> do so upon power-up and then work properly for at least several hours
> without any user-visible calibration (for instance requiring the user to
> step off).
>
> The sensors don't need to determine how much force is being used, only
> whether contact is present.  Ideally the sensors should be directly
> readable using a PIC with analog inputs and minimal external circuitry,
> but any reasonable amount of external circuitry would be fine.
>
> I have been looking at cheap piezo transducers, but I'm not convinced
> that they will be able to accurately detect gradual or prolonged
> contact.  Reading a bit it appears to me that these are unreliable below
> 10 Hz, and I don't know if software tricks would be enough to compensate.
>
> I've also considered capacitance-based non-contact sensors, but I'm not
> sure these could detect contact from heavy rubber boots while avoiding
> false positives from bare feet just slightly above contact.
>
> The only sort of sensors I've seen that would seem to work are
> heavy-duty load sensors, in the neighborhood of $50-$500 each.  The
> budget for the entire electronics portion of the project is $20-50, so
> these wouldn't do.
>
> Any advice is greatly appreciated.
>
> -Rick Luddy
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.