> You make a good point, if I understood correctly, about using
> individually-pluggable wires, with a single-pin on the pcb for each
> one. I did read some posts in one of the pinball or arcade game
> newsgroups, or a website referenced there, about different types of
> connectors, where they were saying/claiming that crimp-type connectors
> for discrete wires are one of the most-reliable types (which includes
> wires with crimped-on pins that are then inserted/mounted into
> multi-connection sockets or plugs). They also claimed that soldering, in
> addition to crimping, is not necessary, and should probably even be
> avoided, since it might do some harm to the connector, or the
> wire/insulation, if not done perfectly.
>
Crimping is only good if you have the right tool and right force etc.
It is too easy to do it badly (like those silly "car electrics" crimp
connectors
where you crimp right through the insulation with flimsy sheetmetal
plyers).
Soldering is said to make the wire easy-breaking due to the heatin, maybe
because
of that it shouldn't be done. However, i have no crimp tools and i trust
my soldering
MUCH more.
> e.g. I also REALLY wanted to be able to see the whole "family" of
> curves, for a transistor, all at once, like on a "real" curve tracer. So
> I eventually figured out how to have a ramp "sweep" signal for the DUT,
> with a synchronized staircase signal for the base/gate.
But you always only show one quadrant? or have you figured out a way of
displaying
a four-quadrant graph? THAT would be nice...
> And I needed multiple voltage rails, so I designed a boost-mode
> switching power supply board that takes 12 vdc and makes the plus and
> minus 18 vdc (variable, actually) needed by most of the ICs (and at up
> to 3 amps, total), and the +5 for CMOS ICs.
IMO it is a bit of overkill to design a boost supply only to require a 12V
supply
before it. I'd just use a +-18V supply then i guess, or make a switcher
for 220V input.
(But you avoid mains voltage which is GOOD for a kit.)
> With all of that working, I decided I also needed to be able to "push
> some more amps" into the device under test (DUT). So I designed a power
> amplifier. And I wanted calibrated excitation-voltage levels for the DUT
> so I made the amp's gain switchable. Then I decided that the resistor
> networks required for switching the gain were kind of "ugly", so I
> designed a coool feedback control loop that sets the gain.
I'm a bit surprised that that was needed. I was not aware that it is
required to
keep the excitation voltage closely regulated. I kind of thought the scope
display shows the
actual values anyway. (e.g. if i make a diode curve from 0 to 1A i can
adjust the excitation
to show up as 1A at the scope - and don't care if it is 1.1A or 0.9A
normally, as the divisions
show that clearly?).
Why is it required to be regulated?
(By the way i would probably have used a multipier to modulate the signal
before the amplifier,
for ramp and triangle it is even easier if one uses opamps to generate the
signal - just
limit the integrator voltage through diodes, you only need 1 more opamp to
invert the voltage.
Have made a frequency and amplitude sweep/wobble sine/sqare generator once
this way. only using opamps.
I avoid "fancy" solutions, because i can't pull the parts out of my
storage then and must order.)
> I also added lots of other stuff, including instrumentation amplifiers
> to sense the voltage and current used for the x-y scope display, and
> inverters, buffers, and switching, etc, so I could display the current
> through ANY of the three DUT leads versus the voltage across ANY two of
> the DUT leads, and flip the displayed polarity of either of them at any
> time.
I'll let the scope do that.
It is sensitive enough, and has diff. inputs to replace the
instrumentation amps,
and invert also. The tek scopes are great for such stuff as i can just
pull out the timebase
and plug in a fully-functional Y amplifier in it's place to generate the X
axis.
> And I added a range of frequencies for the sweep signal. And I added
> twelve selectable current-limiter resistances. And I added an option for
> a triangle waveform instead of a ramp, and an integrator to produce a
> quasi-sine waveform from the triangle. And so on and so on. And on and
> on and on...
That is interesting. I didn't know a triangle can make anything similar to
a sine
after a integrator. (considering the diff. of sine is sine). I'd like to
discuss that.
agreed with the rest.
I want to suggest we carry this discussion to electronics_101, i'd like to
continue it
but it is a bt OT here.
The curve tracer is in the back of my head and i'd like to learn what
functions i need
to keep in mind. Maybe i buy a curve tracer plugin for my scope before i
actually build one,
but you never know (and those plugins are RARE and expensive.)
ST