Category Archives: Audio

Stereo Amplifier

My second attempt at mastering the LM386 Audio Amp IC (still sounds terrible).P1020890

 

Here’s the data sheet for the LM386 IC with some example circuits:
http://eicom.ru/pdf/datasheet/National_Semiconductor_PDFs/LM386/LM386.html

Instructables has a simple how-to:
http://www.instructables.com/id/LM386-Audio-Amplifier/

The schematic used in my project is a variation of this one from:
http://www.rason.org/Projects/icamps/icamps.htm
The only difference is that I added a 100nF from pin 7 to ground.  I think it helps keep the noise down.  There’s also two of everything except R1 and C1.

IMG00001

P1020902 P1020916
P1020911 P1020905
P1020904 P1020914

Wow, my wires are all way too long.  It makes it very hard to get into a tiny box, but it works!

Audio Spectrum Analyzer

There is a great tutorial on how to setup and use a 2×16 LCD on the Arduino website:
http://arduino.cc/en/Tutorial/LiquidCrystal

Here’s a good explanation of FFT theory:
http://www.arduinoos.com/2010/10/fast-fourier-transform-fft/

My pinout is a little different because I wanted to save as many PWM pins to add servo control for the next stage of this project.  I’ve been tinkering with the idea of moving physical objects around based on audio input, instead of just showing levels on a display.

To visualize the frequency levels of the incoming audio signal I use the 8-bit Fast Fourier transform code which is discussed here:
http://forum.arduino.cc/index.php/topic,38153.0.html

Honestly, I’m not convinced that what I’m seeing on the display is an accurate representation of the audio spectrum that I’m listening to, but it looks pretty cool and that’s all I really care about at this point.  There is hardware available that would produce much more accurate results than this software.  There is a “Color Organ” project on the Make website that I’d like to build someday:
http://blog.makezine.com/2010/10/18/circuit-skills-led-color-organ-spon/

Additional Reading:
http://forum.arduino.cc/index.php?topic=38153.0
http://forum.arduino.cc/index.php?topic=182169.0

Code and libraries on GitHub