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listen to light

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antoine magdi

New Member
hello everyone, i'm working on the project of listen to light ,i reached to the attached schematic, can anyone discuss how the circuit operates (in detail plz), because i can't understand where is the source of sound and many other points....
THNX IN ADVANCE
 

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MikeMl

Well-Known Member
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Are you trying to communicate on a light beam by modulating an emitter with voice or music, or are you trying to hear environmental sounds?
 

antoine magdi

New Member
Really it's a small project for the faculty, communicating on a light beam sounds good also (i'm free to choose any project related to my course) so can you give me a hint about this thread?!
 

MikeMl

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Most Helpful Member
Really it's a small project for the faculty, communicating on a light beam sounds good also (i'm free to choose any project related to my course) so can you give me a hint about this thread?!

Read Clint's pages. I have helped him on some of his record attempts. His receivers (and the way he uses photodetectors) is bloody amazing. His receiver is so directional and so sensitive that I was able to hear music modulated onto a 5mW laser pointer at a distance of ~20 Km.
 

antoine magdi

New Member
reply

yahh, it is really amazing, but i think it is more than i need to get full mark :)
so any help for the first project i mentioned (knowing that i got another schematic while googling)
 

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MikeMl

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I predict that all you will hear with that is 100Hz/120Hz and harmonics from incandescent and fluorescent lighting.
 

MikeMl

Well-Known Member
Most Helpful Member
why do you predict that?
and that in the first circuit or in the second?

The second circuit has more gain, which is good. The fact that you are not focused on putting optics around the photodiode means that your optical receiver will be detecting mostly ambient light from all directions simultaneously, and most lighting operates on the power line frequency.
 

audioguru

Well-Known Member
Most Helpful Member
The second circuit correctly has the resistor in series with the capacitor at the output of the LM386 power amp as shown on its datasheet. The first circuit is missing them.

I agree that both circuits will pickup mains hum from mains-powered lights unless you are in the middle of a desert where the noisy LM386 and noisy LM358 will produce plenty of hiss.
 

antoine magdi

New Member
thnx for help but can i replace the lm358 with an op-amp implemented as a current to voltage converter, and the lm386 with an audio amplifier circuit (to be related to my course, i don't want a built-in audio amplifier nor built-in current to voltage converter)
 

Roff

Well-Known Member
If you mount the photodiode in the end of a long tube, or use optics, you should be able to make it directional. I did that once years ago, and could "listen" to the 120Hz ripple of incandescent light bulbs.
You may need some biasing and/or AC coupling on the input stage to prevent op amp saturation.
 
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Sceadwian

Banned
You'd be surprised how modulated the sun is. Try listening to that, probably be your best source for light to listen to. Don't worry about DC bias, it's not as hard to deal with as you might think. Just use a few lenses from true 'grey' sunglasses, or something that is equally 'grey' in the desired passband. The filters you put over the element itself will be the true determining factor of what you get as the output, the straight DC bias from the sun alone is enough to completely swamp nearly any kind of photo detector that's naked to the light, filters are where it's at.. Also record the sound even if you don't hear anything, and then run it through audio software to speed it up. Most light modulated sources aren't audible at normal rates, but create eary and almost whale like tones when sped up. I've listend to some Sun audio clips, they definitely get your attention.
 
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audioguru

Well-Known Member
Most Helpful Member
I would guess that the sun "sounds" like the same snap, crackle, pop and hiss of the noise from a cheap, noisy opamp.
The sun has many solar flares and our atmosphere has hot and cool spots and moving clouds which pass light differently.

Isn't it boring like watching grass grow?
 

stevez

Active Member
I helped my son construct a "light listener" and it provided some insight and entertainment. Along with the hum or buzz of lights was the flicker of candles, noise from TV screen, tone patterns from TV or other IR remote controls, headlights as cars pass by. Next project is a means to listen to bats. While not something I'd spend hours doing it will be an item of interest around the campfire this summer.
 

audioguru

Well-Known Member
Most Helpful Member
I think your version of "entertainment" from hum, buzzes and noises is different to mine. I like music.
I was going to make a circuit to heterodyne the frequency of bats down to audible frequencies until my city got rid of all mosquitoes (with a safe insecticide in all street drains) so the bats are also gone.
I heard a recording of the sounds of bats produced with the circuit and it is just a boring bunch of clicks, buzzes and noises.

Good luck with the mosquitoes.
 

audioguru

Well-Known Member
Most Helpful Member
I like music. Not the hum, buzzes and noise of your "light listener".

I was going to make a heterodyne circuit to reduce the ultrasonics from bats to audible frequencies but my city eliminated all mosquitoes then the bats went away, maybe to your campsite.

I heard a recording of the bats circuit and it was just snaps, crackles and pops. Like Rice Krispies in milk. Boring.

Good luck with all the mosquitoes and other bugs around your campfire.
 

Sceadwian

Banned
Audiguru, what's with the echoing post?
 

stevez

Active Member
When completed I'll have 5 or 6 hours of time invested in the bat "listener" and will likely "listen" to bats for 15 minutes a few times before it gets shelved or loaned to friends for their amusement. For me the real value is in advancing my understanding of electronics. I work all day as a mechanical engineer and need a diversion. I have music going in the shop while building this stuff too. A project this fall could be to construct my own audio amplifiers. I helped a college student with one a few years back and thought it might be nice to employ something homebrew in my sound system. More than likely it would be tube/valve for no particular reason other than it would be what was cool when I was a kid but way beyond my means at that time.

I may employ it in the workshop to listen for air leaks from bike tires. Sure, soapy water is an alternative but gets a little messy.
 
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