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Re: Audio AVC

Jack Purdum
 

Al Peter (AC8GY) and I are working on a new Projects book and in it, I took a few minutes to pull my head out of the sand and look around to see what's happening. Rather than limiting it to the Arduino family, we limited our ?C's to microcontrollers that can be programmed in the Arduino IDE so the reader doesn't need to learn a new programming environment. The book uses the Arduino Nano, but also the Teensy 3.6, the STM32F103, and ESP32 controllers. It is amazing what less than $10 buys in terms of processing power! What I don't understand is why Atmel hasn't come out with a reasonably-priced competitor to these alternatives.

Jack, W8TEE

On Tuesday, April 23, 2019, 2:18:10 AM EDT, MadRadioModder <madradiomodder@...> wrote:


Wow!? Jack is an ESP32 convert!

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From: [email protected] [mailto:[email protected]] On Behalf Of Jack Purdum via Groups.Io
Sent: Monday, April 22, 2019 9:04 PM
To: [email protected]
Subject: Re: [BITX20] Audio AVC

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Exactly. Consider the ESP32 with 1.3Mb of flash, 350Kb of SRAM, all scooting along at 240Mhz at a price of around $6. It also has two DAC ports. While the DAC ports are only 8 bit, it's better than no DAC. Also, you can program the ESP32 from within the Arduino IDE. So far, I haven't found any libraries that don't work with it. Oh, it also has builtin WIFI and Bluetooth.

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Jack, W8TEE

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On Monday, April 22, 2019, 9:37:05 PM EDT, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

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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


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