Sound/Audio Level Indicator

Introduction: Sound/Audio Level Indicator

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In this project, I will show you how to build a simple sound-level indicator using operational amplifiers.

Note: To ask questions, please visit my site at Ask the Expert.

Helpful Supplemental Videos:


  • Dual Power supply or two power supply sources.
  • Proto-typing board
  • Connection wires


  • (11) - 741 Op-amps
  • (10) – 330Ω Resistors or (1) 4116R-1-331 and (2) 330Ω Resistors
  • (1) – 1KΩ Resistor
  • (1) – 1MΩ Resistor
  • (1) – DC-10-IDA (10-bar LEDs)
  • (1) – replacement headphone plug
  • (1) – replacement headphone jack

Step 1: Connect the Amplifier Circuit From the Schematic Below One Part of the Proto-typing Board.

Step 2: Connect the 10-bar LED Display Driver Circuit As Shown Below on a Different Portion of the Board.

Note 1: Area in the yellow box in the schematic represents the area connected in the photo. You will need to connect the remaining 8 using the same or similar connection pattern.

Note 2: The images shows the 4116R-1-331 with the two 330Ω resistors in the lower left area of the image.

Helpful How to Videos:

Step 3: Connect the Output of the Amplifier Circuit to the Input of the 10-bar LED Display Driver Circuit.

Step 4: Solder Wires to the Pins on the Replacement Headphone Plug and Jack.

Note: The plug shown is a mono plug and the jack is configured for a mono input. You may choose to configure your set up for stereo.

Helpful How to Videos:

Step 5: At the Input of the Amplifier Circuit, Connect the Wires From the Replacement Headphone Plug and Jack.Note: Grounds(black Wires From the Plug and Jack and Ground From the Amplifier and Driver Circuits) All Connected Together.

Step 6: Connect the Replacement Headphone Plug to the Music or Sound Source (example: Mp3 Player, Cell Phone, Stereo, Etc.).

Step 7: Connect Speakers or Headphones to the Replacement Headphone Jack.

Step 8: Turn on the Power Supply (or Power Supplies) to Power the Circuit.

Your power supply should be able to produce positive voltages (5V and variable voltage up to at least 10V) and negative voltage (variable to at least -10V).

Step 9: Turn on the Music or Sound Source and Adjust the Volume Until at Minimum One Led Is on When No Sound Is Generated by the Music Source.

Note: See video on how to make the adjustment to ensure one LED is on.

Step 10: Play Sound or Music. Make Additional Adjustments to the Sound Level If Necessary.

Note: Make additional adjustments on the music source.

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