My Homebrew ESR Meter

[Yorkie]

my meter was $6.50 out of hong kong and i thought that was enough to pay. my schematic does have a 22k potentiometer but it does not have the r17 resistor fitted so maybe it does need the 22k pot will not know until i get this finished as to wether it needs that resistor or not depending on the meter used as you said earlierso i have 20 k 25 k and 50 k pot to try in this circuit as i,m thinking resistor 17 was put in place to compensate for the pot size being small in the first place and thah r17 resistor was added to the pot to give it more resisatance???
i do now have the 22k pot also to try with my schematic and have given you the schematic updated version of the original idea so you can now see what i,m building

Hi Marty,

Thanks for posting the updated schematic, which simplifies things compared to the original, and I note the added 100nF cap (C8) on the input to the 7805, which is an easy mod. It can be added across the tracks of any existing boards if problems are experienced, and I'll update the PCB track layout to add a couple of pads for C8 for any future builds.

I think you may be right about R17 - the only thing I can assume was that it was to obviate the risk of damaging the meter needle if the 22k pot was turned to minmum resistance, as when the prods werre touched together, the needle could end stop. R17 would limit the risk of that. However, the einsible thing to do when setting up the meter would be to set the pot to maximum resistance then with the prods shorted together, to reduce the resistance to get FSD on the meter. If it's a preset pot on the PCB, once set, there's no risk of inadvertently tweaking it, as their would be if it were on the front panel.

Your meter was cheap enough - where would we be without internet!

Have fun,

David