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Sense sound and fade LED

Nightshade

Sep 21, 2014
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The circuit that I have in mind needs to sense audio, a persons voice, and flicker or fade many or a single LED on. The circuit will be concealed inside an opaque sea shell. The reason for this kind of circuit is to mimic the necklace from The Little Mermaid (1989) that steals her into a sea shell. So ultimately the circuit would sense the person singing and after a short while begin to turn on the led and after a while longer remain on for possibly a few minutes. I'm going to make a shell out of opaque plastic at around 3-4 inches. Is it possible to make this kind of circuit and around the size mentioned? Thank you for all advise.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Hi there and welcome to Electronics Point :)

Yes, that should be possible.

What kind of batteries are you considering?

How many LEDs? What battery life do you need?
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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OK, I'm not sure that CR2032s are suitable. Could you use alkaline AAA cells? If so, how many could you fit?

What's your budget?

What colour LEDs?

Do you have an idea of how bright you need them to be?

Edit: How are you planning on building the circuit?

Do you intend to make a printed circuit board?

Do you have experience with SMT (surface mount technology) components?
 
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Nightshade

Sep 21, 2014
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Could you use alkaline AAA cells? If so, how many could you fit?
I can probably fit two AAA's.
What's your budget?
It shall be between $50-150.
What colour LEDs?
Probably clear to yellow
Do you have an idea of how bright you need them to be?
It will probably be trial and error. I am thinking of using some type of translucent or opaque polyclay so it will depend on how well the light can penetrate the material.
How are you planning on building the circuit?
Internet order PCB.
Do you have experience with SMT (surface mount technology) components?
I probably wouldn't be using SMT's as I am trying to keep cost down; I know that it would be more beneficial since it is a small space but I think that through-hole pcbs would be more cost effective. I would have to get a third party to utilize SMT's.
 

KrisBlueNZ

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OK. I'm working on a design. But I have more questions. Since you're so good at answering them!

Do you have any prototyping capabilities? Could you assemble a prototype on breadboard and play around with some component values?

I'm a bit unsure about what you want in terms of LEDs. I guess you want to couple them to the shell somehow, so the whole thing appears to glow? I don't know anything about how to do that. You could buy a selection of LEDs, illuminate them (see https://www.electronicspoint.com/resources/got-a-question-about-driving-leds.5/) and experiment to see how many you need, how much current you need to run them at (determines their brightness), and how best to couple the light into the shell.

Be aware that LEDs are available in various viewing angles. Ones in clear packages have a bright light but a narrow viewing angle. Ones in "diffused" packages are the opposite. I would try both types.

I'm assuming this is for some kind of prop for a performance... Will it be used under lighting? If so, it will need to glow pretty brightly.

SMT isn't necessarily more expensive than THT; it just requires more careful assembly. I guess you plan to assemble the board yourself? I can use only SMT components that can be (carefully) hand-soldered. Would that be OK? It could save quite a lot of space.

For the microphone, I like the look of these little MEMS microphones: http://www.digikey.com/product-detail/en/SPU0410HR5H-PB/423-1138-1-ND/2420982 but they aren't leaded. They are designed to be placed directly onto a PCB with blobs of solder paste, and passed through a reflow oven that melts the solder paste to form the connections and mounting. You could (carefully) hand-solder them slightly above the PCB using short wires or pins. What do you think?

How many of these are you making?

What do you mean by "flicker or fade"? The design I'm working on would fade the LED up smoothly while it detects continuous sound, and when the sound stops, the LED would fade out slowly. No flickering involved. Does this sound like what you want?

What is your electronics experience?

Edit: How many CR2032s could you fit into the shell? You'll probably need one for every LED, plus one or two for the circuitry.

Edit2: Have a look at Lithium Thionyl Chloride (LiSOCl2) cells. If you can find a US manufacturer of a suitably small cell, they might be a good option. Each cell is about 3.6V so you would probably need one for every 1.5 LEDs plus one for the circuitry. Their advantage over standard lithium coin cells is their lower internal resistance, which means they can deliver higher current without voltage droop.
 
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KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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OK, here's the circuit I've come up with so far. I'm posting it here in case you're still interested, so you can get an idea of what would be involved. If you want to go any further, answer my questions in post #6.

270397.001.GIF
 
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