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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".

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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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