Re: Going crazy - How does this device work?

On Sun, 29 Oct 2006 14:34:22 -0500, Spehro Pefhany <speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

On 29 Oct 2006 10:44:21 -0800, the renowned "larwe"
<zwsdotcom@xxxxxxxxx> wrote:

I'm going a bit crazy trying to work out how a marketing gizmo
operates. Would appreciate any thoughts!

My local supermarket just installed a small Pillsbury promotional
freezer, roughly cube shaped, and about four feet on each side. On the
side it has the doughboy, and a word bubble that says "Hear me
giggle!". I naturally assumed there would be a microswitch on the lid
triggering a speech module, or maybe a light-gate triggering when you
reach in.

However, it's much, MUCH more subtle than that. If you open the lid,
nothing happens. The thing only giggles when you touch a product inside
the freezer. However, not ALL products trigger it. The freezer contains
mostly cinnamon buns and biscuits, which come in a foil-coated
cardboard tube with steel ends. If you touch one of the metal ends, the
giggle starts. If you touch the tube part, it might or might not start
giggling, depending on whether you touch a shiny part or a printed
part.

There happened to be a non-metallized cardboard box of frozen pastry in
the freezer also; handling that box, picking it up, moving it about,
etc. did not trigger the voice.

The inside of the freezer is all plastic, so I don't think it operates
by making the contents one plate of a capacitor. My best guess is some
kind of microwave motion/prox sensor, but I'm damned if I can work out
the details.

Pretty much has to be capacitive, IMO. Maybe picking up (or shunting)
something with your body capacitance.

Since just putting your hand inside does not trigger it, perhaps it
has something to do with the shelves? Does touching them trigger it?

I would think that touching a metal object would produce a fairly rapid change in capacitance over
time compared to inserting your hand, which ought to be detectable.

.