AVR Spectrum Visualizer Project

Nate Graff

Created as a final project for Cal Poly CPE 329

What does it do?

Displays the magnitude of the audio spectrum from about 700 Hz to about 3 kHz on an 8x8 LED Matrix

What parts does it use?

• ATmega328P (courtesy of an Arduino Duemilanove)
• MAXIM MAX7219CNG SPI-Interfaced 8-digit 7-segment display driver
• 8x8 LED matrix, common-cathode (Vf ~ 2.0 V, If ~ 20 mA)
• Adafruit Electret Microphone Amplifier - MAX9814 with Auto Gain Control
• 28 kohm resistor

Can/Should I build one?

Yes/No. Don't use the MAX7219CNG. Get a prebuilt 8x8 matrix controller module and use that. The pinout of this chip is inane. If you do use a better matrix driver, you'll need to modify the encode_display() function, which transforms the vram matrix to match what I had to do to have a sane wiring harness.

I want to use the MAX7219CNG, how did you wire it?

What FFT Library did you use?

I used Open Music Labs' Arduino FHT Library. I used the Hartley transform so I wouldn't bother wasting cycles computing phase data.