Project site: diy.elektroda.eu/analizator-widma-akustycznego-v2/
And here is how it works on 20*2 VFD
"czulosc" and "janosc" are in polish, they means "sensivity" and "brightness" :) And they can be changed :)
Step 1: Make Board
Step 2: Program the AVR
Step 3: Connect Audio Signal
a) Signal ground to “Agnd” on board, in this case analayzer ground and audio ground can not be connected together.
b) Analyzer can be powered symmetric, +-2.5V, “Agnd” will become power ground and audio ground.
c) If analyzer and our output device grounds must be connected together, and there is no way to power analyzer with symmetric supply, you must somehow raise signal to 2.5V height. You can do this by connect the grounds together, raise the signal up with R/R resistor divider (about 100Kohms) connecting them between gnd and supply, signal through 1uF capacitor to resistor divider and then to IN pin.
Step 4: Fast Calibration
Left potentiometer set so that was leaning out just one bar (eventually two, depends on frequency), highest as possible. If gain be too large, you will see other leaning out bars – this is bad. Now, change generator frequency to 10KHz, and right potentiometer set in the exactly same way. Done.
Step 5: Precision Calibration
You will need two programs “function generator” and a “oscilloscope”. I use “FG Lite” and “Oscilloscope 2.51 for windows 95″ (on download page). Learn the basics of using a oscilloscope, how to setup line-in of your pc audio card, how to set a input gain of audio card and oscilloscope so that there was no overdrive – i will not describe that here – if you do not have an idea on what i am talking about, just make the fast callibration.
Function generator set to sine, frequency 5KHz, gain at about 80% (on picture there is 400Hz, don’t mind that).
Left potentiometer turn right to the end, connect line-in of your pc audio card to RED point.
3rd image show how should look a proper clean signal
And 4th image show how look a overdrien signal with tops cutoff
If potentiometer is turned right to the end and despite that signal is overdriven, you will have to reduce signal from your pc, or, if nalayzer will be working in other device, you will have to add R/R divider or extra potentiometer to reduce the signal strength to proper value. If the signal is nice and clean, try to raise it a little bit by turning the potentiometer in left direction – but do not overdive. Do the same with the right potentiometer and GREEN point. Now, connect your pc audio input to BLUE point and then to YELLOW to check if signal is ok. At the end check if low-pass filter is working corectly, connect your pc audio line-in to YELLOW point, and slowly move the frequency slider from left to right, signal should vanish near 800Hz – 1KHz.
Step 6: Jumper and Other Options
I am the author of hardware and part of the software, author of software is Hunterhouse user.
Source codes are included
All needed files are in the attachment. I know my english it's not too good, so ask if something is unclear.
Oh, and if you want fast response to your question, please ask in comments on my site or contact me.
ATTENTION ATTACHMENT WAS UPDATED. Previous contained a little bug in programms.