Back in the 1990s, I had a pretty little battery-powered swing-a-ma-bob decoration. Only problem, it ran down batteries in an egregiously ungreen way, so I cobbled together an AC-to-DV power source for it using an unused block plug, and rather than the typical soldered-on connections and plugs, some flat bits of copper and sections of wood dowel that snapped in place of the original AAA batteries, and insulated ribbon wire thin and flexible enough to pass the edge of the battery compartment cover.

Happy with the (which ran constantly for nearly a decade ‘til wearing its plastic swingy bits to ruin), I had ambitions of packaging (more slickly than bare wood and copper) and selling the arrangement in a world-changing entrepreneurial tour de force, but being pretty a flea- market-grade entrepreneur, if that, never realized it. A bit of googling suggests that nobody else did, either, or if they did, didn’t rise to fame and fortune from it.

Nice as this snap-in-place-of-batteries external power system is, it has a downside of turning a pretty desktop decoration into a pretty decoration with a thin cord running from it to a wall socket. So instead of that, this: same-size battery replacement powered by ambient wifi signals.

A quick source check suggests this is asking a lot – a typical wifi receiver has about 0.0001 W received power, while a nominal 6200 J AAA battery discharged over 60 days gives 0.0012 W – but maybe not too much.

This idea is at best a silly variation on a serious, promising idea in the oh-so-sexy internet of things family of ideas
-- CraigD, Oct 11 2014

Mobile Gadgets That Connect to Wi-Fi without a Battery http://www.technolo...-without-a-battery/
Aug 2014 MIT Tech Review story with some serious thoughts on Wifi power [CraigD, Oct 11 2014]

Swinging Sticks Kinetic Energy Sculpture http://www.thinkgeek.com/product/e060/
A product page for arguably the best loved swing-a-ma-bob decoration much sold to date [CraigD, Oct 11 2014]

Wifi power harvesting http://www.pratt.du...ergy-electric-power
I doubt this will fit in your device. [sdk16420, Oct 13 2014]

100 uW, but then there are conversion losses as well. You're describing a crystal set, but operating at 2.4Ghz, where parasitic capacitance has huge effects. And 802.11 uses a GPSK modulation schema that spreads the energy over a frequency range.

It's doable, but you need a local CW transmitter with a tight frequency control and no modulation. Good luck getting a frequency out of the FCC or the DTI for that.

A magnetron would be a good cheap-and-cheerful source, but you'd have to hold the power way down - in the milliwatt range- to avoid undesireable surface heating effects. And it's pretty directional.

There might be some scope in the 27Mhz AM band in some jurisdictions.
-- 8th of 7, Oct 11 2014


I love it when you talk like that.
-- normzone, Oct 13 2014


I had to fan myself a bit too.

But back to the idea: I like a crystal set powered by your own wifi. Wifi bases must differ in power. Surely the big ones for convention centers have more oomph than the one over there by the piano. Or take a regular wifi and turn it up to 11?

I suspect that the original device described here is one of those apes that pedal along a tightrope.
-- bungston, Nov 08 2014



random, halfbakery