"Roy J. Tellason" bravely wrote to "MIKE ROSS" (25 Oct
03  04:06:11)
 --- on the heady topic of "ESR meter"

 RJT> MIKE ROSS wrote in a message to Roy J. Tellason:
 MR> :   ESR adaptor for DMM

 RJT> Not bad except that it's slightly screwed up in the middle,  I'm
 RJT> guessing tabs where there should be spaces?  Something like that?

I looked but didn't find a tab in the original edit. It was probably a
linewrap issue. Let me see if I can't narrow the width a little.
Here goes nothing:

:   ESR adaptor for DMM
:   -------------------
:
:           o +9V *regulated
:  ,--------|
:  |        |
:  |  .-----------.
:  `--:4    8    3:-----+-3K9--+----o------> probe
:     :           :     |      |    |
:     :   "555"  6:--. 10K     |    |   set DMM to
:     :  timer    :  |  |    200R (DMM) 200mV AC
:     :     1    2:--+--'      |    |    range
:     `-----------'  |         |    |
:           | 3n3F* ===        `----o------> probe
:          _|_       |             _|_
:          ///      _|_            ///
:                   ///


 RJT> Yeah.  I can see where it would be possible to do some more circuitry
 RJT> to give an indication,  even if it were something as simple as a
 RJT> unity-gain buffer with rectification,  so that you're only trying to
 RJT> read DC at the end of it.  A freq of 100k ain't _that_ far out there.

I was aiming for very low parts count on the theory that the more
junctions there are the more work it takes to build something. I'm one
lackadaisical sob! ;-)

In your track of thought however, consider a bad electro will exhibit a
much higher resistance than 0: usually in the 10's of ohms and above. A
marginal electro would show something less than 10 ohms and a good
electro between 0 and 1 ohms.

So we have 3 ranges of indication which could just as well be replaced
by 3 leds, red, yellow, and green: respectively for bad, marginal, and
good. But having an actual resistance reading is interesting for
measuring other things than capacitor esr.


 MR> The only critical part is the voltage supply which must be a
 MR> regulated 9 volts.

 RJT> Don't have any 9v regulators but there are *lots* of 7805 (and even
 RJT> 78L05 which I'm sure would suffice for this) around here...

Well, a 9 volt alkaline battery is pretty good regulation but the
trouble is that it does drop a bit over its lifetime. However, this may
not be such a big problem since we aren't trying to measure highly
accurate ESR resistance values but nearly a "go/no-go" device.


 RJT> I collected a bit of other ESR meter info from other responses to that
 RJT> initial post,  but I've snagged so darn *much* info off the 'net in
 RJT> the past few days that I'm currently in the process of trying to get
 RJT> it organized,  before I go out and get some more.  Nice to have a
 RJT> local HTML tree here...    

The "drinking from a fire hose" analogy is quite apt. Try my circuit
first and let me know what you think.

 Mike
 ****

... Real techs don't lick nine-volt batteries!
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