Re: [CAD_CAM_EDM_DRO] Re: Mostly on topic or at least getting there

> > I just bought a Tek 475 scope for working on a servo setup I'm
> building
>
> The PC monitor is not very much different from the tube for an
> oscilloscope, so setting up a PC as a scope should be very feasible.
> Anyone knows of any affordable PC base scope?
>

Actually, monitor and oscilloscope CRT's are vastly different.
Monitors use magnetic deflection and scopes use elecrostastic. The
high voltage in monitors is derived from the sweep coils, which makes
it hard to make the display brightness consistent over a wide range of
scan rates (a multisync monitor may tolerate a scan rate variation of
at most 1:4 - a scope has a range of perhaps 10^8 or more.

More realistic are the digital sampling boards that in conjunction
with software turn the entire computer into a scope. These are good
for their ability to store, save, analyze, etc waveforms. One thing
to be wary of though is that many (most of the affordable units) of
them do not have anti-aliasing filters on the inputs, or if they do
have a filter it only corresponds to the maximum sample rate and does
not track as the sampling rate is changed. (The proper method is to
keep the acutal sampling rate fixed, build a corresponding hardware
filter, and do software filtering followed by decimation to simulate
lower sampling rates when requrested by the user - but this requires a
DSP chip or gobs of memory).

This means that you can get some very misleaded distortion of the
signal unless you think very carefully about what you are doing.

I've seen the manual for one handheld LCD scope which tells you to
start at the fastest sampling rate and decrease the rate only until
your signal appears.

Chris