Oscilloscope question

Tony Duell ard at p850ug1.demon.co.uk
Wed Apr 13 17:48:05 CDT 2005


> The Tek 7000 series scopes are really, really, undervalued these days
> for what they represent.  I got a fast 79xx mainframe at auction last
> year for $5 because it had weird plugins (the Logic Analyzer plugins,
> without the pods- useless) in it and didn't look much like a 'scope' to

Actually, those pods are relatively 'benign' in that the signals to the 
analyser are differential 10K-seriea ECL signals. It's not hard to make 
up TTL-compatable input adapters, etc.

Not as good as the real pod, but better than no analyser at all.

> Students these days don't learn squat about using analog scopes, and

Tell me about it. Actually, I am not sure what students _do_ learn these 
days...

> there is a LOT you can do with one if you know how.  Delayed sweep,

As I mentioned the other day, I've never used a DSO for real work. I've 
always made do with an analogue scope, and I think I know how to do some 
useful things with it. 

My view is that you'll not get the best out of a DSO unless you fully 
understand the use of an analogue 'scope (in much the same way that the 
best users of CNC tools are darn good machinists on manual machine 
tools, in the same way that the best designers using CAD systems are also 
the best designers without CAD systems...). 

> external trigger, etc. are there for a reason, and worth getting
> acquainted with.  With delayed sweep and the Differential Comparator
> plugin (introduces a DC offset so you can look at the 'important' part

Now why do you think I have 1A5 plug-in for my 555 ? 

> of the waveform at high gain) you can zoom in on tiny windows of
> repetetive waveforms as well as (better than, actually) any digital
> scope.

And it's amazing how many signals can be made repetitive. A friend of 
mine (a darn good hacker) debugged his homebrew 68K system with an old 
Tekky analogue 'scope. He repeatedly pulsed the reset line to his system, 
and connected that to the external trigger input of the 'scope. He then 
looked at particular signals, 'scrolled through' them with the delayed 
timebase and figured out what the processor was doing. 

You can't always do tricks like that (which is why DSOs are sometimes 
very useful), but many times you can.

-tony



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