Electronics > Beginners
Analog VU Meter & Volume Pot
vidarr:
The audio source will be a mobile phone or tablet most of the time. If the sound is decent, I may use it at one of my computers. It is mostly for watching news, not movies or music, so the sound doesn't have to be amazing.
The meter really is just for fun because I have it. I just want to learn how it works and how to create a circuit for it. I think now, with your guys' help, I am starting to get a good idea. I read things online, but sometimes asking a simple question and getting a simple specific answer helps a lot. I looked to a lot of schematics with VU meters and see how they work, kind of. But I had a lot of "why" questions that I never find answers to.
Thank You
bob91343:
vidarr, I respect your attitude. If you want to learn, it's best to get into it with your hands and make stuff happen. Lessons learned this way are far more durable than conversation.
So if you risk blowing the meter, you have learned something. It's just a motor but only goes about a quarter turn before hitting the stop. And on power removal, the spring brings it back to starting position. The secret is the spring; that allows the motor to turn just so far before the spring holds it back.
Since the motor is very sensitive, it's also delicate. Too much current can overheat the fine wire in the armature, and cause mechanical shock when it hits the stop.
Since it only responds to dc, you have to rectify the signal if you want it to respond to ac. Actually, most rectifiers also pass dc so you kind of have both worlds when you use one.
vidarr:
I already burned out so many things putting circuits together wrong, including two (and a half) power supplies and three transformers (and many other random small parts). I really like this VU meter, so it will suck throwing it in the trash. I am still soldering the rest of the circuit and building the aluminum and wood housing. I have another week or so before the VU meter part of the project starts. I read the article floobydust gave the link for. He provides a number of circuit options and then at the end says none of them are good except maybe one. If I had a cheapo meter to mess with, or a simulated meter online...
Thank You
Richard Crowley:
--- Quote from: vidarr on August 31, 2019, 02:21:02 pm ---Where do VU meters typically go to "avoid" this?
--- End quote ---
We use VU meters (or the modern equivalent) while mixing sound for "production" of a finished product.
The finished product may be a recording (cylinder, disk, cassette, CD, MP3, etc.)
Or it may be a live program (broadcast, network, online, streaming, etc.)
But in any case there are certain constraints and standards for audio levels.
If the audio levels are too low, then the Signal-to-Noise Ratio (SNR) suffers and the result is noisy.
But if the audio levels are too high, then they distort and clip from running into the limits of the system.
So the VU meter was developed to monitor audio levels to keep them in the "sweet spot".
Not too low "down in the mud" of the noise-floor, and not to high, distorted and clipping.
In the digital era, it is even more critical to avoid too high = clipping.
At the destination end of the system (the audience), the audio signal is re-constituted.
At some point, the audio signal is at the same ratio as when it was created/transmitted.
But then the end-user has a "volume control" where they can select some portion of the original level.
If you can connect your VU meter BEFORE the volume control it will represent the level of the original program.
But if you put it AFTER the volume control, it will only represent your prefered listening level.
Now, that may be what you want, but only you can decide how to connect/use the meter.
Audioguru again:
I use a peak detector circuit to correctly show the actual maximum levels of my LM3915 logarithmic 10-LEDs sound level meter that shows sound levels since it has a microphone and preamp for it.
I added a circuit to boost the sensitivity 10 times when levels are low.
Unfortunately the LM3915 is not made anymore.
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