From: grarpamp <grarp...@gmail.com>
>Free power of course...
>https://science.slashdot.org/story/16/07/14/2049246/cleanspace-co-sensor-runs-on-freevolt-rf-harvesting
>A few years ago, a Kickstarter was set up to develop a locator tag
>powered by free radio frequency (RF) energy harvested from the
>environment. This was called a scam here on Slashdot and was shut down
>before it was funded on Kickstarter. However, it now appears that the
>concept is not as far-fetched as some predicted. A UK company
>CleanSpace has developed a carbon monoxide (CO) sensor which is
>powered by free RF. A review of the product has been posted on
>YouTube. It uses Freevolt technology to keep a battery charged and the
>CO sensor running. Since they have several thousand of these devices
>collecting data, they do appear to work and it seems to be in the 'not
>a scam' department.
I don't think there's necessarily a contradiction here. While there do exist
CO sensors which needto keep the detector heated to 400 degrees C, and
therefore benefit from being connected tothe AC supply, "electrochemical cells"
which have extremely low power consumption are nowavailable.
https://en.wikipedia.org/wiki/Carbon_monoxide_detector The device needs merely
to 'wake up' occasionally, maybe every minute or so, interrogate the voltage on
the electrochemicalcell, and sound the alarm if the limit value is exceeded.
The main concern is ensuring that the detector has enough power at the time it
is necessaryto alarm to sound that alarm. The ongoing (non-alarm) power
consumption is probably much less than the self-discharge rate of a battery.
Modern alkaline-cells have a shelf-life of in excess of 5 years, andperhaps as
much as 10 years, although Wikipedia doesn't state this
specifically.https://en.wikipedia.org/wiki/Alkaline_battery
http://data.energizer.com/PDFs/non-rechargeable_FAQ.pdf
In contrast, a tracking device must actively emit some sort of signal to alert
some remote system toits current location, which takes power. It must also
somehow know where it is: GPS receivers use much less power than they once
did, but even that is far greater than that which a tiny battery couldbe
expected to provide.
And the amount of power available from "free RF" is obviously quite variable:
If you're 0.5 kilometeraway from a 50Kw television transmitter, that's a lot of
signal strength. Compare that with out inthe boonies, 1 km away from a
cell-phone tower is not a lot. It would make more sense to designa CO detector
with solar cells on the bottom, and have people mount it on an outside window,
with a rechargeable battery to store enough to get through the night.
Jim Bell
