http://xoscope.sourceforge.net/

This a free program for Linux. It very ingeniously uses the microphone
input on most computers as an analog to digital converter.

At 44,000 samples per second it is ideal for trouble shooting electrical
problems on our rotary powered airplanes.

Hook it up to the crank angle sensor and you
can see what is happening. This is a common source of problems
with Tracy's EFI system.

Hook it up to the stock Mazda rotary knock sensor and you
can see knock waveforms if any.

You can connect it to the ignition pulse coming out of
Tracy's computer and measure the dwell time. Use two resistors
as a voltage divider so you don't damage the sound card.

You can check the signals going to the injectors. Also
use a voltage divider.

You can attach it to the avionics bus and see if glitches appear
as you turn things off and on.

I downloaded it and automatically installed it on Ubuntu 10.04
running on my EeePC 1000 in 30 seconds. After I plugged in a microphone
and whistled it was working.

If you have a full size computer with a stereo sound card I think
one might be able to look at two signals simultaneously.
I have not tested that feature so far.

Real O scopes cost hundreds of dollars and thousands for the
high end versions.

This one is free if you are smart enough to be using Linux :)

I would not be a bit surprised if it showed up on Android (Linux) tablets
soon.

Paul Lamar

THANKS!  This looks great.

Any idea if one should use more than an attenuating resistor as an
input-isolation device to protect ones computer (I once fried a
capacitor on a motherboard when a tantalum capacitor broke down and sent
high voltage into my home-made PC).  A little opto-isolator chip might
be in order.

R Berglund

I don't know how linear an opto idolater would be. I never
fooled with one in the linear mode. Might work fine.

Paul Lamar