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Old 4th April 2011, 10:58 PM   #1
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Default AGC automatic gain controler

hello everyone
im trying to make a AGC for audio signal out of:

digital potentiometer MAX5455
op amp 084 GP
u controler PIC16f877

my idea, to make it clear, is to automaticly put more, or less, gain to make the audio input be always the same at the output

i thought about using the comparator module with an interrupt fonction.
So when the signal is over a certain limit, is rises a flag, which one will be use to drop the gain.

BUT, for the undervoltage.. im out of idea
I thought using a lower reference and then if the flag is off rise the gain
but if there's an other option i'll take it for sure

my signal have no offset and the opamp will have pos/neg alim
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Old 5th April 2011, 12:40 AM   #2
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doesnt really matter but it is a PIC16f877a, not 877
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Old 5th April 2011, 12:45 AM   #3
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Unless it is a special purpose app I would go with one of the "analg engines" like the THAT2180. E
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Old 5th April 2011, 02:37 AM   #4
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Default Easier Solution ???...

If you want your MP3 files to play at constant perceived audio level use MP3 Gain - freeware that will scan your MP3 files and set them to a preset playback level....cures a lot of issues.
https://sourceforge.net/projects/mp3...5.exe/download

Eric.
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Old 5th April 2011, 04:48 PM   #5
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its for an analog signal eric.. thanks for the idea
THAT2180 has a voltage controlled gain.. it is not an AGC
the probleme is to detect undervoltage to ventually put more gain, any help ?
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Old 5th April 2011, 05:38 PM   #6
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A VCA stage is the basis of AGC....a derived control voltage drives a VCA stage so as to provide constant output level.
Google is your friend.....audio agc schematic - Google Search

http://www.thatcorp.com/datashts/dn118.pdf

Eric.
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Old 5th April 2011, 06:04 PM   #7
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You don't need a microcontroller to do this... and you are not using proportional control? Just a hi-limit comparator? You'll never know how much to adjust the gain.
I would use the SSM2166 compressor/limiter IC: http://www.analog.com/static/importe...ts/SSM2166.pdf
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Old 5th April 2011, 09:11 PM   #8
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sorry eric i misunderstood the THAT2080, i looked back at it, it seems good.

though i dont really need a constant output, i just need it to be inside my irs2092 range, i thought that with these peices i had, i could do something good, and i know i dont need a uctrl :P but i have some unused output in my circuit, so i wanted to use them to make a homemade agc with that digital pot i had in hand,
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