Can Some Help Explain This Circuit to me? its a LED Audio VU meter circuit

[SammHunka]

If anyone could help, that would be amazing. its not homework, its a personal project i am undertaking and just wondered if anyone could give me an explanation or any help if they had any understanding of this circuit! thanks guys!

Samm

 

[schip666!]

It would of course help to know the chip number or whatever...

But I'm not sure what needs explaining? It looks like it takes an audio input, through a "volume-control", compares it to a reference set with two resistors, and then (maybe?) lights up an array of LEDs based on the strength of the input.

Do you have some more specific questions?

 

[uart]

The chip is an LM3915 and yep it's just a bunch of comparators set to switch in the LED's at different levels of the input signal. The circuit is pretty much the datasheet example for this IC. Not really much to explain.

 

[AlephZero]

It would of course help to know the chip number or whatever...

That's what "LM3915" on the circuit diagram means.

The circuit is straight from the datasheet http://pdf1.alldatasheet.com/datasheet-pdf/view/8899/NSC/LM3915.html

What specifically don't you understand?

 

[SammHunka]

Basically i just need help understanding what the reference dc voltage connected to the top LED is for, what the variable resistor is for, and basically how the overall circuit works (meaning how the output is created through the lm3915). sorry about the mix up!

 

[schip666!]

That's what "LM3915" on the circuit diagram means.
What specifically don't you understand?

I don't understand how I managed to miss that is what I don't understand...

 

[davenn]

Basically i just need help understanding what the reference dc voltage connected to the top LED is for, what the variable resistor is for, and basically how the overall circuit works (meaning how the output is created through the lm3915). sorry about the mix up!

the DC voltage connected to one side of ALL the leds is the + power supply for those LEDs

The variable resistor is to set the gain/level of the input to the chip so that you don't overdrive it. overdriving it could ...

a) damage the input to the chip
b) mean that ALL the LED's would be permanently lit up so you wouldn't have any meaningful variation in the LED display

Dave

 

[SammHunka]

Thank you dave and the rest of you guys! presenting it to my peers tomoro so i will check back with how it went! much thanks!