Doing AGC in software would incur added delay, especially with an i2c pot on our beloved little Nano.
We want to keep the attack time as short as possible.
Would be fun to try, perhaps using one of the small ARM processors with fast embedded ADC and DAC capabilities.
Jerry


On Mon, Apr 22, 2019 at 05:45 PM, Hasan Murtaza wrote:

Technically the simplest circuit (for some people) would be a software solution. Send the amplified output to a diode plus capacitor in a peak detector configuration. The capacitor voltage will be a quasi DC signal proportional to the maximum value of the signal. Read it into the arduino via an ADC pin.?

So far, component count =2.

Next replace the collector resistor in the class A common emitter amplifier with a digital potentiometer. Control the pot resistance (and hence the transistor amplification) with a digital output pin of the arduino. Write some software to set the gain based on the measured peak output voltage.

Total parts count is 3.?

If you sample the audio voltage directly you can do even fancier tricks like computing rms value or histograms etc.

Hasan