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voice activated led circuit with lm386 and lm3914

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danielphantom

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Hello, I have seen a circuit including the two chips above that acts like a "visual effect" associated with a science fiction "universal translator". I have a functioning board that my friend bought and only see a few resistors, caps, and the two ic components. I thought it would be fun to try and breadboard a similar circuit.

When you speak the microphone (little condensor mic I believe) picks up your voice and you see the leds light up (there are 6 Leds.) With softer sounds, only one led lights up, as the volume increases--you see more and more leds light until they are all lit when you speak with a loud voice.

I have tried to hook up a basic 20 gain and 50 gain and 200 gain 386 amp and send the signal into pin 5 of the lm3914 but have had no luck at all.

I tried to make a simple amplifier with the 386, with a speaker attached with the above gains and I get a tremendous squealing from the speaker when I test it. I understand that this is unwanted oscillation and can be caused from a variety of things. I read that a cap across the battery terminals can solve some of this but bottom line I would like to know can you just simply output the 386 into the 3914.

any ideas? suggestions would be greatly appreciated.

thanks,

Daniel
 
A simple web search comes up with this circuit which looks like a reasonable approach, though I have not reviewed it, or built it. You have to pay attention to circuit layout and wire length with high gain amplifiers. Keep input leads physically apart from output leads and all leads as short as practical. Use single point grounding.

I would use a 3916, not a 3914 because the 3916 had log taps more suitable to how the human ear responds to sound, and thus looks right to the human eye.

If you put the speaker near the microphone, you will hear a squeal due to the sound from the speaker entering the microphone, getting amplified to the speaker, again entering the microphone, on and on. The squeal is called feedback.

FX567GSFLROK12R.gif
 
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out of all the searches I made, I never found that, thank you so much. I'll give it a try. The current built model I have is made with a 3914 and seems to be very responsive.

thanks again

Daniel
 
You have an INSTRUCTABLES schematic that is completely wrong (like most Instructables).
Look at the datasheets of the ICs to get it correct.
 
I got a working prototype going on the breadboard, thanks so much....yes I have the 3914 wired a bit differently but it is nice to see it go. now to get it on some perfboard, my buddy wants to build a few for him for some spare change:)
 
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