Audio input conditioning...

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#1
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I'm looking to design a small (physically) and preferably simple AGC to precondition a line audio input before it gets to a uP ADC or ZCD input. Lo-Fi is acceptable - what I'm really looking for if a reasonable input dynamic range and an output that is uP-friendly, A pair of diodes is not enough!

I have thought of fully-integrated devices such as the SSM2166, but these are expensive and I really don't need that level of sophistication as I'm only looking at 8-bit ADC or even just zero-crossing sensing.

Traditional solutions have tended to involve transconductance amps and a peak level detector, but I was wondering if there was any really simple way of doing this...

Cheers

[while an AVR maybe the ultimate goal for the signal this isn't really about using AVRs per se so I'm going to move this to General Electronics - Cliff]

Nicko

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So if you have a Programmable Gain Amp feeding the a/d, and the gain bits are controlled by the AVR, you have a digital closed loop AGC, and we are back on the AVR topic.

Imagecraft compiler user

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Nicko,

A spooky coincidence. Today on the Eaglecad yahoo group I saw the circuit below. I cannot vouch for its suitability or the legitimacy of the owner's parents, dog licence, or ... anything else. Buyer beware.

Cheers,

Ross

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Ross McKenzie ValuSoft Melbourne Australia

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valusoft wrote:
Nicko,

A spooky coincidence. Today on the Eaglecad yahoo group I saw the circuit below. I cannot vouch for its suitability or the legitimacy of the owner's parents, dog licence, or ... anything else. Buyer beware.


Thanks - this is a design from an application note - the opamp gain is controlled by the FET which is essentially being used as a voltage controlled resistor driven by the DC peak voltage fed into its gate. Its one of the implementation patters I was referring to.

Cheers

Nicko

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There's the NE570 compandor, but I don't know if that is still made.