Hypothetical question, can't talk much about specifics all very hush hush...
If one had some kind of photoelectric effect device, photo transistor, solar cell or who knows, and one put it right up to a LED that blinked, say a white LED of a half watt or so, much energy could you expect to extract best case?
Would it be enough to power up a low power microprocessor for a quarter of a second?
On Wed, 27 Jan 2016 00:52:40 -0500 (EST), bitrex Gave us:
Better off with a solar cell and a supercap.
That totally depends on the time that it will be allowed to collect the energy.
Say it blinks half of the time and the LED has 30% efficiency and you use a solar cell operated in its maximum power point then my estimate (YMMV) is a conversion efficiency of roughly
1/2 * 1/2 * 0.3 * 0.1 * 0.5 = 0.0037 W or 3.7 mW (the last 0.5 for 'other' losses).An energy-efficient microprocessor (
So yes, it should be doable.
joe
Sorry, I should have deleted the previous sentence after doing the calculation below...
joe
Depends how efficiently you can couple the LED to the PV cell(s) and how slowly you can afford to run the CPU. You main problem would be stepping up the voltage to run the CPU (or illuminating multiple cells).
Might as well use a blue LED since there is no point down converting photons to red and yellow with a phosphor in this case.
Yes. If you are suitably frugal about it. There are not many CPUs that will run on 0.6v though.
On Wed, 27 Jan 2016 08:26:37 +0000, Martin Brown Gave us:
There are CPUs that run really fast and all on a few milliamps of current and next to none when idle.
With off the shelf parts? I think you might get a few percent of the current. (maybe 1-5% (?)) and then you loose the voltage drop from LED to photodiode.
George H.
Interesting! Thanks
This IC looks pretty interesting (PDF):
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But then you can put some solar cells in series. Or buy this one:
joe
So why are we helping to design a surveillance device?
Cheers
Phil Hobbs
That sort of transfer efficiency seems reasonable. The LED spectrum should reasonably match the solar cell curve, so a white LED might not be best. Some uPs will run from very low power.
Two or four series PVs might be needed to get a couple of volts to run a small cpu.
Magnetic or capacitive coupling would be easier.
The intended purpose I have in mind is about as far away from that stuff as you can get!
I have a strict no cops/NSA/DOD policy.
Yeah an IR led might be better. They spit out a lot of photons too.
I don't get the "hush hush" part.
George H.
How about ex-GFs?
Cheers
Phil Hobbs
Sure, why not?
Same rate as everyone else, though.
Mostly a joke to cover for the fact that this is just a weird middle-of-the-night-idea, and I don't actually have any idea what I'm doing ;)
This was solved in the 1980s. Grab any solar calculator, they run fine with less than a half watt LED.
But it would be just a pulse, not continuous.
When connecting solar cells in series, you have to ensure equal illumination on _all_ of them.
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