Hi,
i was following this thread with great interest and decided to build an esr meter, because i liked the idea of cutting out the inductive voltage spikes i decided to build a version similar to oldboys last design. Being only a prototype i didnt bother to make a pcb but just started building the circuit on a copper clad board. At the moment i am still testing the thing but it seems to work fine, it has a full range of only 4.2 Ohms but that is ok for an esr meter because when a cap has an esr higher than that i do not really care how high anyway. It works good to below 10µF, and a 150nF Cap still reads slightly over 1 Ohm ( the orange one in the picture ).
The resistors i measured in the pictures are:
1 Ohm 10% --> 1,018 Ohm --- i measured this Resistor to 1,014 Ohms with another meter
3,3 Ohm 10% --> 3.347 Ohm --- measured this one to 3.347 Ohm and calibrated the esr meter with it
0.062 Ohm 10% --> 0.061 Ohm
0,180 Ohm 10% --> 0,184 Ohm
0,120 Ohm ?% --> 0,119 Ohm
The resolution and accuracy of this design could be increased by using a precision voltage reference (i rely on the ouput of the LM7810 i use)
and not using cd4066 as a switch, but i like the results and will use it in the future. Usually when repairing stuff i don't rely on esr measurement anyway but look at the voltage across the elkos with a scope to see if they are good, but for quick measurements a reliable esr meter is a good thing to have, so it will suffice for my needs.