Question about Op-Amp

  • Thread starter Rainier9
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  • #1
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Hi again, I have a little question about op amps and using them as ''Adders''.

I currently study EE and Communications Engineering but our class still hasnt gone to the point of op amps. We will get there by the end of this semester. But we are asked to do a projects about everything we've learned in the past classes. My idea for the project is rock stage/platform light system.

The project will have many modules but one of them is a VU-meter. The issue is that rock bands usually have at least 5 active instruments at once, and I need a single VU meter.

Can I add the 5 signals using an OP AMP and then inserting the sum'ed signal to the VU-Meter IC?

Keep in mind that i dont want to use the mixed signal to listen to the music, I just want it to go to the VU meter.

Im using a LM3914 Driver for the VU meter.
 

Answers and Replies

  • #2
berkeman
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Hi again, I have a little question about op amps and using them as ''Adders''.

I currently study EE and Communications Engineering but our class still hasnt gone to the point of op amps. We will get there by the end of this semester. But we are asked to do a projects about everything we've learned in the past classes. My idea for the project is rock stage/platform light system.

The project will have many modules but one of them is a VU-meter. The issue is that rock bands usually have at least 5 active instruments at once, and I need a single VU meter.

Can I add the 5 signals using an OP AMP and then inserting the sum'ed signal to the VU-Meter IC?

Keep in mind that i dont want to use the mixed signal to listen to the music, I just want it to go to the VU meter.

Im using a LM3914 Driver for the VU meter.

Sounds like a fun project. One way to look for circuits is to use Google Images. Go to Google Images, and search on opamp adder. You will see that indeed the circuit you want is very do-able.

You will want to rectify the input signals first, to give you DC-like signals to add. You will also want to figure out how fast you want your VU meter to respond, and tune your input rectifier circuits to that bandwidth. So you are rectifying the audio (20Hz-20kHz or so) and making a DC-like signal that has, say, a 5Hz bandwidth or so to feed into the adder stage.
 
  • #3
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Thanks for your feedback, but woudlnt rectifying the signal making it impossible for the VU meter to drive the LEDS as it would be a constant current?

I dont want to have a LED of the VU meter to represent an instrument. I just want the VU meter to be able to function properly independent of the number of instruments.
 
  • #4
berkeman
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Thanks for your feedback, but woudlnt rectifying the signal making it impossible for the VU meter to drive the LEDS as it would be a constant current?

I dont want to have a LED of the VU meter to represent an instrument. I just want the VU meter to be able to function properly independent of the number of instruments.

That's where the "bandwidth" of the displayed signal comes in. How fast do you want the VU meter to be able to move? The human eye can't see movements that are too fast, so that's why I was picking a ballpark of, say, 5-10Hz.

The "rectification" would have a resistor in parallel with the smoothing cap, to bleed off the charge at that 5-10Hz rate. (For each channel that you are conditioning before the adder).
 
  • #5
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Oh, I get what you mean now. Thanks a lot for clarifying.
 
  • #6
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Thanks for everyone's help. We finished the project in early may of the year, I thought some of you may wanna see the end results, so here's a quick video!




The VU meters are the lights at the sides and the top. The other lights are activated by movement.
 
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  • #7
309
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Thanks for everyone's help. We finished the project in early may of the year, I thought some of you may wanna see the end results, so here's a quick video!




The VU meters are the lights at the sides and the top. The other lights are activated by movement.

Looks impressive.

What's a VU-meter?
 
Last edited by a moderator:
  • #8
32
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Thanks xD
It's a Volume Unit meter. It displays the intensity of the sound.
 

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