Using a microcontroller to monitor VU levels

[Pilbromatic]

Ok, so I'm working on a preamp system. Basically, what I'm after is some way to record VU levels with a microcontroller.

I've found this thread here: http://www.diyaudio.com/forums/showthread.php?postid=606297

This however, is the OPPOSITE to what I'm after.

What I want to do is feed an audio signal into the circuit, and have some means of linking it to a microcontroller, either using I2C, SPI, or some sort of direct connection.

So far, I'm thinking of either using some sort of op-amp fed into an ADC and connecting that via I2C or SPI to a microcontroller, or, even easier, using a uC with an onboard ADC.

As for my own findings, I've found some ICs on Microchip's site, such as the MCP3424 or TC514. I have no idea if these would do what I'm after, but the quad inputs appeal to me! Another thing I found was the MCP6S28, which is cool with 8 inputs, but I don't think it even comes close to what I want. Basically I get a bit lost when it comes to ADCs etc!!!

Has anybody seen this done before? I've been searching for ages and can't find anything remotely close!

Thanks in advance for all your help!

 

[jackinnj]

You can get the MCP3424 evaluation board for $15.00, the serial analyzer which may be used with it is another $49.99

 

[Mr Evil]

I made a microcontroller-based VU meter once. I used a PIC12F683, which has a built in ADC. I could dig out the schematics and source code if you want.

 

[Pilbromatic]

I made a microcontroller-based VU meter once. I used a PIC12F683, which has a built in ADC. I could dig out the schematics and source code if you want.

Awesome! If you don't mind that'd be cool. Thanks!

 

[Pilbromatic]

You can get the MCP3424 evaluation board for $15.00, the serial analyzer which may be used with it is another $49.99

I'll look into this actually, might be a good way to go!

Another thought was possibly a TAS3103A, although I think this is quite different again.

Either way, I need 8 inputs for this particular project, so I could use a larger uC or two PIC12F683's, whichever way I go. I think a single uC with 8 analogue inputs could be my best bet. Those schematics etc would still be handy so I've got something to base my designs on though. 🙂

 

[Mr Evil]

Here you go then. It was designed to be used inside a PC, so it has rather heavy filtering on the voltage supply, and it's split into several sub-boards that stack on top of each other to save space. The LEDs are driven by a separate chip which communicates over SPI, but you could drive them directly from a larger microcontroller.

Bear in mind that I only did this with a uC because I wanted to improve my abilities with them; it would have been easier to use a dedicated VU meter chip.

First, this is the analogue section - two op-amps and a pot for level adjustment and buffering.

 

[Mr Evil]

Next, a voltage reference to provide 2.5V from the 5V rail.

 

[Mr Evil]

The LED driver.

 

[Mr Evil]

This is the main board with the PICs on. Unfortunately Kicad has decided to mess with the symbols for the PICs so the pins don't line up now. Going down from the top right, the pin numbers should be 7, 6, 5, 4, 3, 2, and on the left had side from the top 1, 8.

 

[Mr Evil]

And finally, the source code. It displays both peak and VU at the same time. All the VU calculations are in software, to minimize the amount of analogue circuitry required. Fortunately even the small PIC I used was fast enough for this.

 

[jackinnj]

Apropos of the June 10 post on your website -- I trust you have seen the following Gordon Ramsay YOUTUBE:
http://www.youtube.com/watch?v=BaOZ...DBC057B6E&playnext=1&playnext_from=PL&index=3

 

[peranders]

High-End Solution

You could also use a ADC with built-in VU meter. Cirrus had at least one model where you could get out dB data. Don't remember which number CS53??

 

[jackinnj]

Re: High-End Solution

You could also use a ADC with built-in VU meter. Cirrus had at least one model where you could get out dB data. Don't remember which number CS53??

TA7318P is around -- it's a SIP dual meter driver peak-reading VU or power

http://datasheets.weeqoo.com/TA7/TA7318P.pdf

I saw some available a while back.

 

[Pilbromatic]

Re: Re: High-End Solution

Firstly, let me say - Thanks heaps!!! you guys are total legends!

Thanks for that Mr Evil - It gives me something to chew on for a while!

TA7318P is around -- it's a SIP dual meter driver peak-reading VU or power

http://datasheets.weeqoo.com/TA7/TA7318P.pdf

I saw some available a while back.

Cool! I've just been scouting around for said Cirrus ICs. I got sidetracked - I didn't think of Cirrus, they have some cool stuff! I didn't actually find the DACs with the VU outputs as mentioned, but it is 2:30am on Friday where I live at the moment, so I'm getting a bit sluggish!

Thanks heaps again though everyone!

 

[Pilbromatic]

Argh, I meant ADC, not DAC. As I say, getting tired!

 

[Mr Evil]

Apropos of the June 10 post on your website -- I trust you have seen the following Gordon Ramsay YOUTUBE:
http://www.youtube.com/watch?v=BaOZ...DBC057B6E&playnext=1&playnext_from=PL&index=3

We have thousands of those damned things in our garden. It would be nice to put them to good use, but somehow I don't think I could bring myself to eat one.

 

[jackinnj]

We have thousands of those damned things in our garden. It would be nice to put them to good use, but somehow I don't think I could bring myself to eat one.

Sell 'em to the folks across the Channel

 

[glt]

Would Arduino work? It has built in 10-bit ADC.

 

[Pilbromatic]

Would Arduino work? It has built in 10-bit ADC.

Hey, that's quite cool! I can get them from on of my local suppliers it turns out - Could be fun to play around with!

But it's just based around an ATMEGA8, I think I've got a couple of those floating around.

In answer to your question, yeah, I think it will work. But these have so much unnecessary componentry.

I think I'll just go with getting a large-ish uC and use the built in ADCs. I don't see why it won't work, and a few people say it will.

Thanks though! I might build/buy one of those Arduino boards to play around with though. 🙂