Mar 282017
 

Audio level indicator using LM339

This audio level indicator using LM339 circuit is very interesting, because it allows us to visualize the audio level intensity by connecting this circuit to the output of a loudspeaker.

The LM339 integrated circuit has 4 comparators that operate completely independently but share the same voltage source.

This voltage source may be in the range of 2 to 36 volts. The This IC also works with two voltage sources +/- V (dual voltage source) as long as the sum of the two voltages is not greater than the maximum allowed.

Audio level indicator using LM339

How the audio level indicator using LM339 works?

The circuit has three outputs. Each of them is connected to an LED through a resistor. The green LED turns on first, then the yellow LED for medium signal levels and when the signal voltage level is the highest the red LED lights up.

A LM339 integrated circuit is used to achieve the objective. This integrated circuit has 4 comparators that can be powered with a single polarity voltage source.

The input signal is applied to a resistor-potentiometer network which is used as a voltage divider, controlling the amplitude of the signal that is applied to the first comparator. C2 capacitor blocks any direct current voltage component.

The first comparator is used as a follower. On this way it is possible to have the same signal at the output of this comparator as the input. The advantage is that this comparator has a very high input impedance and does not loads the output of the amplifier that powers the loudspeaker.

The output of the first comparator is connected to the inverter pins of the other three comparators. On the non-inverting pins of the 3 comparators, 3 potentiometers are placed, which are used to set the voltage level that determines which LEDs will light up. By adjusting the four potentiometers of the circuit the desired effect is achieved.

List of components of the Audio level indicator using LM339

  • 1 LM339 IC, 4 comparators (IC1)
  • 3  470 ohm resistors (R1, R2, R3)
  • 1  330k resistor (R4)
  • 1  1.2M resistor (R5)
  • 1  470K resistor (R6)
  • 1  100K potentiometer (VR1)
  • 3  500K potentiometers (VR2, VR3, VR4)
  • 1  1uF electrolytic capacitor (C1)
  • 1  100nF capacitor (C2)
  • 3  LEDs, red, yellow, green (D1, D2, D3)
  • 1  9 volts battery or a 9 volts voltage source.

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