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'[PIC] Multichannel VU meter chip?'
2007\10\12@162305 by Harold Hallikainen

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I'm wondering if a multi-channel (perhaps 8 channels) audio level metering
chip (VU meter) with an SPI interface exists. It would be great if the
inputs were differential so they could be hung across a balanced audio
line. A PIC will then pull this data and update a graphic display. Right
now we're looking at individual balanced rectifier and filter circuits
driving analog inputs on a PIC. LOTS of parts! It'd be great to just have
one chip handle the whole thing. Another possibility would be run all this
into a DSP and calculate the levels, but, if a chip is already out there
that does this, it'd be great!

Searching the usual suspects doesn't seem to turn up anyting.

Ideas?


THANKS!

Harold



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2007\10\12@170234 by Robert Rolf

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Harold Hallikainen wrote:

> I'm wondering if a multi-channel (perhaps 8 channels) audio level metering
> chip (VU meter) with an SPI interface exists. It would be great if the
> inputs were differential so they could be hung across a balanced audio
> line. A PIC will then pull this data and update a graphic display. Right
> now we're looking at individual balanced rectifier and filter circuits
> driving analog inputs on a PIC. LOTS of parts! It'd be great to just have
> one chip handle the whole thing. Another possibility would be run all this
> into a DSP and calculate the levels, but, if a chip is already out there
> that does this, it'd be great!
>
> Searching the usual suspects doesn't seem to turn up anyting.
>
> Ideas?

Ummm, aren't you building this chip yourself? DSPIC with SPI interface, and
8 channels of A/D. Sample audio at 44khz, then rectify and filter digitally.
You can put the needed prefilter into the differential to single
ended op amp circuit.

Why would you use balanced rectifiers and filters?
Just do a balanced to single end conversion at the start and cut your parts
count in half.

Latest 'ideas for design in EDN mag) has a circuit for using a single transistor
to do full wave rectification (just bias it right and use right gain set resistors).

Using software for the whole thing gives you the advantage of being able
to change the filtering, if needed.

R

2007\10\12@185258 by Harold Hallikainen

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{Quote hidden}

Thanks for the comments! I'm hoping to find a chip that already does the
job, but can either do this in analog hardware or software. The balanced
rectifier is an ideal rectifier circuit with a differential input. Our
incoming audio is balanced, not single ended. I'd like a chip where I just
feed it 8 balanced audio signals and all the VU levels show up on an SPI.
I may end up doing it in DSP. I'd probably still need the differential
amplifiers for each input.

Thanks for the comments! Any more?

Harold

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2007\10\15@153601 by alan smith

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This might work as your front end?  TLV320AIC34 from TI, so you can TDM data out

Harold Hallikainen <spam_OUTharoldTakeThisOuTspamhallikainen.org> wrote:  
{Quote hidden}

Thanks for the comments! I'm hoping to find a chip that already does the
job, but can either do this in analog hardware or software. The balanced
rectifier is an ideal rectifier circuit with a differential input. Our
incoming audio is balanced, not single ended. I'd like a chip where I just
feed it 8 balanced audio signals and all the VU levels show up on an SPI.
I may end up doing it in DSP. I'd probably still need the differential
amplifiers for each input.

Thanks for the comments! Any more?

Harold

--
FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
opportunities available!

2007\10\15@155110 by Harold Hallikainen

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Thanks! We already have codecs in the system. 24 bits for a VU meter seems
a bit much. I think I'll mess around with a 24H chip, letting it do the
ADC and calculations.

THANKS!

Harold
The ideal design has zero parts


{Quote hidden}

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