"John Popelish" wrote in message
...
robb wrote:

Also i do not know how one would fix the capacitive load to
preven oscillation ? The only solution i recall for these
oscillation prolems is adding a capacitor ? hopefully my
addition
of small cap across opamp will solve both problems ?


Thanks for John,


If it was my board, I would add provision for a resistor
between the opamp output and the pair of capacitors so that
I could try adding a 10 to 47 ohm resistor. If it works
without any, you just jump that component

Then run the ground buss directly from the capacitors, not
from the opamp output. It won't be a stiff, but then, the
battery is not a stiff voltage source, either.

easy enough for me, will do,

Unfortunately, this is not the only circuit weakness, but
you seem intent on getting something built, rather than
refining the circuit, first.


yes, you are correct.
This was originally meant to be an SMT PCB etch and build
project.
This was one of the ?better ?(free) ESR schematics i could find
on the net.

*but* i am not opposed to learning something ... this just seems
a little heavy for an amature hobbyist.

To do some learning i suppose i would first try to understand
exactly what ESR is technically ? (besides an indicator of
capacitor health)
Then study how ESR could/would be measured by some circuit.
Then i would read up on OpAmps what they do and how they work,
maybe build some simple OpAmp circuits, change things watch input
vs outputs on a scope/meter/etc.
Then i would study each individual block of the Quad OpAmp in
this ESR schematic to understand how and what each piece does
individually.
Then maybe i could go on to understanding how those pieces work
to gether to solve the original problem (how a circuit would
measure ESR). and so on

and i would love to do all that but "tai-yai-E-yime is not on my
side"

I still struggle with resistors, capacitors and transistors
and i do a mind bend into some fluid or hydraulic translation
like ...
Resistors are constrictors with pressure and flow tolerances
Capacitors are surge tanks with pressure (charge) , flow and
surge volume tolerances
Diodes are one way check valves
etc....

For instance, I think it
might be quite practical to eliminate the ground bus half
way between +4.5 and -4.5 volts rails, all together. Most
of the circuit is only using the +4.5 to ground part of the
battery voltage, and the ground reference generator has to
waste the other half by absorbing their currents.
The capacitors connected directly to an opamp output is the
first clue that the designer has not finished thinking the
circuit through.


So it really is not that great an ESR schematic then ?

Well i really wanted to build something good and would rather not
build a crappy ESR.

Then I am dropping back and will read through comments made. I
will probably re-draw schematic in OpAmp block form as in the
original schematic then figure out what the pieces are doing by
reading through the OpAmp application notes Joerg pointed to etc
etc etc....


Thanks for the help John.
I hope some of you experts are going to be around when i ask
"what for is a resistor ?" and other such basic questions.

robb