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How do I make an LED volume indicator?

post #1 of 5
7/13/10 at 11:29pm
Thread Starter 

I'm trying to make an array of leds that light as my volume goes up, but I can't find any schematics or how to's for how to do this.

 

Here's an example of one I found on youtube.

 

 

Thanks a bunch!

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post #2 of 5
7/13/10 at 11:40pm

3914battmon[1].gif

 

This is the simplest I know of

 

cheers

FRED

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post #3 of 5
7/16/10 at 12:34am
Thread Starter 

So I'd put the output from the pot into the input of the LM3914?

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post #4 of 5
7/16/10 at 8:01am
Quote:
Originally Posted by getllamasfast View Post

So I'd put the output from the pot into the input of the LM3914?


No, the diagram calls for a 12V DC feed into a separate pot at the LM3914's input, in order for the display to behave like the video.  If you connected the output from your volume pot to LM3914's input, then you'll have a VU meter with a dancing display (to the music).

 

If you want to make your volume knob behave like in the video, then you need an extra gang to your volume pot to make this work.  If you use a stereo (dual-gang) pot for your volume control, then you'll need a three-gang pot.  Those are uncommon, so you might have to get a four-gang one.  Also note that the LM3914 has a linear display range and require a linear taper pot, but it's also rare to find a pot that has two audio (log) taper gangs for your audio signals but additional linear taper gangs on the same shaft.  Maybe get a quad audio taper pots and a linear taper pot of the same model range, disassemble them and transplant the guts (assuming a pot that could be taken apart non-destructively).

 

You should read the LM3914 datasheet for more info about what that chip does and how it works, also look at LM3915 and LM3916.  Go to National Semiconductor's website and search for these by part number.

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post #5 of 5
7/17/10 at 3:30am

LM3914 is't suitable for audio - it have linear scale. LM3915 has log scale (which is fine) and LM3916 has special audio -20dB +3dB scale

Read the datasheet for application note.

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