In the LED bar display, we will be using the display driver LM3915 as well as a ten LED display array.  The LM3915 is a monolithic circuit that senses analog voltage levels and drives ten LEDs, providing a logarithmic 3 dB/step analog display.  The whole display is able to operate from a single voltage supply as low as 3V or as high as 25V.
 
 
 
The DIP ackage of the LM3915 is shown above.  Below is the required connection for the IC to act as a LED driver in the bar mode.  The variable resistor is adjusted to get the required display level for a certain volume.  Typical values suitable for the variable resistor is 10k or 50k ohms.  The input to the LM3915 can be tapped from the output of the preamplifier.

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