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Author Topic: Science fair project - flashlight  (Read 2032 times)
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For all those students searching for a graduation project, they should watch this idea from a 15 yr old

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Think it is great!
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Rob Tillaart

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Wow. And outside on a cold night it would be brighter. Pretty good.
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Another video with more technical content:
Unfortunately, the technical content includes quantitative data; she gets about 5mW; enough to run each of the 3 LEDs at about 0.5mA each.
That makes it a pretty great science fair project, but not a very practical flashlight.
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That makes it a pretty great science fair project, but not a very practical flashlight.

I disagree.  At 1:40 she claims "five foot candles of brightness" which, according to the OSHA and Phillips websites, is bright enough to move about but not bright enough to work (about right for an emergency flashlight).
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That makes it a pretty great science fair project, but not a very practical flashlight.

Maybe with the help of some components (switch capacitor ...) one could extend the device to have a "harvesting mode" to collect energy and a "shine mode" to use the energy.

Or connect several "harvesters" to one group of leds.

I was also thinking of a "head-band" version...
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Not verbatim but I think I got the key points;
Quote
40s Step1: How much heat per cm sq our bodies radiate, I found this to be around 5mW
I needed only 0.5mw to obtain a good LED brightness.
55s Step2: Characterisation of the peltier tiles, I found that both tiles produced sufficient energy but only around 2mV,
I needed around 2.5V
1:07s Step3: final circuit has only 4 components. I obtained a good LED brightness with less than a 50mV input and around a 50% efficiency.
1:20s Last Step: 5mW of power 5 foot candles of brightness

No moving parts, no charging required, simple construction, I like this.
How do the numbers in the above stack up, could people use this to move about safely at night and how cheaply could it be produced?
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What I am curious about is how 2mV became 2.5V, especially with only 4 components. How would that be done?
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Step 2 said "a few millivolts", not "2"; later she says her step-up runs from 50mv input.  (which is quite impressive, BTW.   Most step-up circuits need an input voltage of at least a transistor Vbe; about 600mV.) (Hmm: http://circuits.linear.com/64 )

"foot candles" is a lousy way to measure light output.

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could people use this to move about safely at night
It's hard to say.  Those single-LED keychain lights are generally around 100mW;  I've been in situations where they seem ridiculously bright, and also situations where they were not nearly enough (keychain lights are NOT sufficient for exploring lava tubes!)  Arguably, the light of the full moon is enough to "move around safely", and it's pretty dim.

One of the nice things about this, as a "science fair" project, is the fact that most people should be able to reproduce the results.
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She said the peltiers gave 2mV and at the end she said she got good brightness with only 50mV though she wanted 2.5V.
Would 50mV give a good brightness.

She mentioned 50% efficiency. Did she mean she only obtained 50% of the 5mW/cm sq she thought the body produced?
Is 5mW/cm sq reasonable?

At the end of the day she showed a working torch. The output looked poor but it looked on the verge of being usable.

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One of the nice things about this, as a "science fair" project, is the fact that most people should be able to reproduce the results.

So the circuits, calculations etc. will be published?
Do you know where?
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This looks pretty complete: https://www.googlesciencefair.com/en/projects/ahJzfnNjaWVuY2VmYWlyLTIwMTJyRAsSC1Byb2plY3RTaXRlIjNhaEp6Zm5OamFXVnVZMlZtWVdseUxUSXdNVEp5RUFzU0IxQnliMnBsWTNRWXA2ZVVBZ3cM
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You see the bulbs against dark in the video. You don't see them illuminate anything but the camera element. Try lighting a white led with 2.5V at 2mA (5mW)... she uses 3.

I'd like to see a bigger one with a cap so it can be filled with cool or cold water.

A hat or headband with peltiers on skin (forehead and temples) would give more area and heat, 30% of your body heat goes out through your head (a good hat in the cold is worth a lot), body heat is not the same for all skin. Our brains are real pigs.
Also check the inside of the wrist as opposed to the palm, and armpits (where you put your cold hands to warm them up even through a coat) and some other places I won't mention.
Areas with fat won't do so well though.
If you could get significant area, you could really be bright.

Getting around in the woods at night without a flashlight was one thing we learned in Scouts back in the day, but there's some nights when a light like that would really help like no moon and overcast/raining. I spent my last 3 or so years in Scouting without one, camping every month and one summer over 8 weeks and never missed having one.
Give your eyes time to adjust, you'll be surprised at how much wider and less claustrophobic the view is without a damned flashlight.
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If this gets second place.. then what does a 15 year old need to do in order to win? Invent the next iphone? I'm very impressed!! smiley
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She could call it the iTorch. smiley

Powered by "I".
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Deep within the bowels of Apple, a corporate lawyer's trident just flickered red.
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