About a Diy pc oscilloscope found on the Net

If you can save the wave with their software, you can do FFT with

trial version is free, something like $35 to own it! I recommend it highly, I've been using it for years!

At a second look at that circuit, the A/D chip has only 8 bit resolution. That's not going to give you much of an FFT!

Hello

How much bit are need to do FFT ?

Thank

Gaetan

with

resolution.

The Nyquest theory states you want to sample at a rate of at least twice the highest frequency you want to see.

Hi

Here's what they said at the scope web site;

Key Features

Sampling Rate 100K Samples per second

-5 V To +5V Input Range

-50V To +50V Olerload Protection

8 Bit Resolution Scope Timebases:100uS/Div To 100mS/Div Scope Volts/Div: 100mV/Div To 5V/Div Works with ANY parallel port

Thank

Gaetan

site;

So, a 50 KHz Nyquist frequency. A little better than twice what you get from the input port of your sound card, at much lower resolution (16 bits is 256 times the resolution of 8 bits, and 16 bit sound cards are commonplace). In Canada, as in the US, you ought to be able to find analog oscilloscopes for $50 or less at yard sales or eBay; that might be a better use of your money.

I've used the input port of a sound card as a low-frequency digital scope. It worked, for example, to see the encoding on the magstripe of a credit card, by hooking up the read-head of an old tape player to the microphone port of my computer and dragging the card across it. This was years ago, and I had to write my own software. Nowadays you have freeware like Audacity that will do that part for you.

site;

Hello

I mostly want to do spectrum analysing of distortion, I have a sine wave oscillator who have less than .0003 % distortions. Most soundcard do have quite high distortion to do that with a software, and buying a spectrum analyser adaptor for an oscilloscope cost quite to much for me.

Thank

Gaetan

John Bordynuik cut and paste " I mostly want to do spectrum analysing of distortion"

Hello Gaetan,

Consider using fast ADCs (>20 Mhz ADS1610 or something), parallel interface or differential, then capture the data on the PC using an inexpensive (but fast) PCI DIO card. This solution would cost you less than $600.00 if you built it yourself.

I just finished a 128-channel unit.

Regards,

John Bordynuik CPU Architect JBI

I'm afraid you wont be able to detect such distortion with equipment that is less than $20000....

--
Jean-Yves.