Arduino Forum

Using Arduino => Audio => Topic started by: artvolk on Mar 16, 2011, 08:06 am

Title: Amplifier/rectifier/filters advice needed
Post by: artvolk on Mar 16, 2011, 08:06 am
I'm looking for circuit to amplify and feed signal from electret mic to ADC. My goal is to detect is sound level is above some threshold to detect quite loud screams.

I've found two amplifier circuits:

First on the one BC337 from here: http://tinkerlog.com/2007/05/20/cheap-sound-sensor-for-avr/
(http://gyazo.com/60854de25af811240b784dae306a0c00.png)

Ant the second on LM386 (audio amplifier\op-amp) from here: http://tinkerlog.com/2007/10/22/diy-tengu-on-a-breadboard/
(http://gyazo.com/275162c7f442becfc3100b6aae8d163b.png)

I've found great schematics here in forum: http://arduino.cc/forum/index.php/topic,52978.msg378412.html#msg378412 unfortunatelly without values for components.

Before building I'd like to ask some questions:
- It seems that negative part of waveform will be feeded into ADC with transistor circuit?
- Does circuit with LM386 have shift in output so values will be always positive (in code he subscract 512 so I assume it have bias)?
- Can I place envelope detector (http://en.wikipedia.org/wiki/Envelope_detector) after LM386 circuit, how to calculate values?
- Can I use the same circuit with line-level audio signals?

Thanks in advance!
Title: Re: Amplifier/rectifier/filters advice needed
Post by: johnwasser on Mar 16, 2011, 12:48 pm
Here is a one-transistor amplifier from the Playground:  http://www.dtic.upf.edu/~jlozano/interfaces/microphone.html

This example, also from the Playground, use an IC amplifier: http://didier.longueville.free.fr/arduinoos/?p=1057
Title: Re: Amplifier/rectifier/filters advice needed
Post by: artvolk on Mar 18, 2011, 08:57 am
Thanks for the response, both circuits from your links seems to come without biasing and envelope filter, is it good for ADC?

Thanks!