MIKE ROSS wrote in a message to Roy J. Tellason:

 MR> "Roy J. Tellason" bravely wrote to "MIKE ROSS"
(25 Oct 03 
 MR> 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?

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

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

Looks good,  I can even quote it without wrap...   :-)

 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.

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

Simple is good,  no argument about that...

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

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

Hmm.

 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...

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

I wondered why you picked that voltage,  too.

 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...    

 MR> The "drinking from a fire hose" analogy is quite apt.

Oh yeah!  I'll get online,  read and reply to email,  read and reply to
newsgroups,  and heaven help me if I click on any links,  because then I
start finding interesting stuff...     :-)

 MR> Try my circuit first and let me know what you think.

Not without at least a look at the alternatives!  :-)

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