16 Jun
2006
16 Jun
'06
12:51 a.m.
Tony Duell wrote:
Ah, cool! Mine are showing their age. Aside from CMOS and
HiNil, most stuff of it's vintage was different flavors of
TTL. I'd have to look at the schematics to see if the
thresholds are ratiometric or driven by real references.
[Analogue .vs. ditial multimeter]
Yup. This usually happens exactly *once* -- the first measurement
I make. Then, a suitable pejorative accomplishes the fix! :>
Meter has scales for .2K to 20M by decades (.2, 2, 20, 200, 2000,
20000) plus "auto". Also have to be careful to select 2 wire
vs. 4 wire measurements, etc.
(sigh) Too many buttons. And do I really *need* 5.5 digits?
(I think not! I don't keep it calibrated that often to
be able to use that much acuracy)
(grin) Agreed. I've got a Fluke 8840A and
it is really hard
to NOT wait for every digit on the display to settle down!
OTOH, if I pull out my Simpson 260P, the needle ballistics
are damped enough that you get a pretty quick "feel" for what
the number is.
Yep. Trying to get some voltate to maximum or minimum is a right pain
with a digital meter :-)
Oen other point. Most good digital meters are autoranging. Make sure you
can lock it on a particular range (or seleect the ranges manually, or
both). Habing it switch ranges and shift the desimal point halfway
through a measurement will drive you insane. As will waiting for it to go
from the highest resistance range to the lowest when you're doing
continuity checks (think about it...) >>> 2)
A logic probe
[...]
Of course, it really works best with traditional
TTL instead
of newer logic families (but, it's good enough to give you
a quick indication of "dead" lines, etc.
One of the advantages of the LogicDart is that you have selectable
tresholds on the inputs. OK, all three channels have to be set to the same threshold (it's actually quite rare that this
causes a problem). The
insturemtn has pre-defined thresholds for TTL, 3.3V and 5V CMOS and ECL,
and you can also select your own (I used it to debug the -15V discrete
transistor logic in the HP9100, for example).
]...]
I usually use mine with different CPU adapters. If I know I am
going to be doing something particularly "involved", I put
headers on the target and just run ribbon cables from the pods
to the target.
Problem with most logic analyzers is getting all
the microhooks
(or easyhooks) that go with it. Without having to sell a kidney!
Tell me about it. Unless you're insane (as I am), don't get a logic
analyser without the 'pods'. Making those is an interesting exercise in
high-speed analouge design. And only consider doing it if you know --
exactly -- the input spec of the main analyser unit As regards the clips, I was lucky, Greenweld (back
when they were in
Southampton) had some at a silly price (\pounds 1.00 for 10 or
something). I bought their entire stock [1] and passed them on to
friends, etc (no I don't have an more left, only the ones I need for my
own alanyser)
Yeah, I saw some micro grabbers here at 50c/each but decided that
buying 200 of them was ridiculous!
[1] I did the same thing when they had brand new,
boxed, Emulex Q-bus
SCSI cards foe \pounds 10.00 each. I bought one, showed it to the system
manager wehre I was working (he was a serious DEC heed), and he basically
told me to go back the next day to buy the rest. I did. Again, I only
have a couple left for my own PDP11s....
<grin> I did that with chrome audio cassettes... bought 2000 of
them in one lot. Amazing how much space 2000 cassettes take up!