[sdiy] yard sale find

[harry]

Theo wrote:

(and is gonna get a butt-kick for  ;^)

> <sni> As long you don't work with high voltages you don't need a 10x probe.

Arrgh. BIGGEST mistake you can make.  The purpose of the 10X probe is
almost NEVER to allow "higher voltages"...  its to allow the probe to load the
circuit with 10X the resistance (1/10 of the load).

The scope probe is a resistor (and capacitor) to ground.  This makes for some
VERY REAL loading effects.  Tie 1 megohm to ground on your VCO, VCF, and its
dead-in-the-water... (not damaged, but not working correctly either).

Even the 10 megohm resistance of the 10X probe is sometimes too much. (you can't

-for instance... look at the voltage on a sample/hold capacitor... just will not
work)

So use the 10X probe whenever possible for the best measurements.  Use 1X
only for a very very low level, low impedance signal... if you must.

Its also a bad idea to use unshielded wire for scope connections... unless you
are very sure of what you are looking at... (like across a speaker output you
will not see any problem).  If you tie that antenna to a sensitive spot in a
circuit,
it can introduce noise, radio, cause bizarre oscillations from stray
capacitance,
inductance... etc...

(sorry Theo for the buttkick. You needed that  ;^)

I recommend an inexpensive, 1X / 10X probe. Set it to 10X for everything except
that ONE rare time you can't see the signal, even at the highest scope gain...
then
try 1X and be in serious doubt about your readings... (don't trust them)

H^) harry