m kinsler wrote:

I'd like to try building an oscilloscope from an old CRT monitor or TV
set. The purpose would be to display audio waveforms at one of the
science museums I work with; there's no calibration necessary.

I've tried the various sound-card based 'scope programs available for
the PC, and none of them show sufficient detail; I really believe I'll
need an analog device to show things like the difference in the audio
waveforms of different musical instruments. The big screen of a TV
set would be helpful for demonstrations.

I understand that this is a totally novel concept, and that Google
doesn't yield a single thing on the subject except for the twenty-six
thousand articles listed under "TV oscilloscope."

But I must say that those plans seem either oversimplified or more
theoretical than practical. The problem I keep concerning myself with
is that the deflection yoke of a CRT is, or at used to be, part of the
high-voltage circuit.

Additionally, we run into the problem that a magnetic deflection coil
is an inductance, and thus won't accurately show, say, a waveform
that's not pretty darned sinusoidal. I would imagine that any corners
on a waveform sent into a vertical deflection coil would be converted
into spikes.

So I'm lazy. Has anyone actually done this sort of thing and actually
had it work to any degree? Thanks.

M Kinsler

I built one of these about 20 years ago based on a kit in Electronics
Australia. Basically a complete time wasting exercise. With a sound card
and a PC and one of several sound analyzing pieces of software you get
an out of this world result, compared to even old sound/vibration
analysis hardware from HP or other makers. If you need a TV screen just
to show the class then use a video card with TV capability or one of
them modern plasma/LCD flat screens with VGA in.

regards Andrew