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I'm working with this design.

I would like to make those LEDs into LED bar graphs that will show the intensity. For example, I want a song with a loud base to make the bar graph shoot up to the top. The bars of the LED bar graph I would like to just be individual LEDs. I was getting the effect with an arduino but I was hoping there was easier way to do this.

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LM3914 / LM3915 / LM3916 will do this job directly. There are other ICs that will do similarly. Search for "bar graph driver".

enter image description here

These will interface more or less directly in place of the 2N3904 transistors in your circuit. (Just as the SSR's would that I provided references to yesterday). Some minor component changes may be needed.

  • LM3914 - linear

  • LM3915 - log response

  • LM3916 - "extended logarithmic" VU meter type display.

NatSemi product page

Also lists I^2C only (not analog input) LP3944, low voltage, 8 LEDs. LP3943, low voltage , 16 LEDs.

Datasheets:

IIC only - LP3943 product page

Pricing - Digikey, in stock

Note below - display can be a bar or individual dot at selected level.

Edited relevant parts from LM3914 overview. Others similar

  • Drives LEDs, LCDs or vacuum fluorescents
  • Bar or dot display mode externally selectable by user
  • Expandable to displays of 100 steps
  • Internal voltage reference from 1.2V to 12V
  • Operates with single supply of less than 3V
  • Inputs operate down to ground
  • Output current programmable from 2 mA to 30 mA
  • Input withstands ±35V without damage or false outputs
  • LED driver outputs are current regulated, open-collectors
  • Outputs can interface with TTL or CMOS logic
  • The internal 10-step divider is floating and can be referenced to a wide range of voltage
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There are easy to use integrated solutions like the LM3914 If you look at it's block diagram inside the datasheet you'll see the basic idea. A Single voltage reference, a resistor ladder and one opamp (used as a comparator) per output.

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    \$\begingroup\$ Why do you say "opamp used as comparator" instead of "comparator"? They might well be real comparators, the symbol is the same. \$\endgroup\$ – Federico Russo Aug 10 '11 at 8:15

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