Wingnut built an Equivalent Series Resistance meter based on this design. He made a couple mods to the original design to get better performance:
I used a LMH6619 opamp for the oscillator, this is rail-to-rail output/input and 35mA current sourcing. This allows for a wider voltage swing and better drive capability compared to standard opamps. It was salvaged from another project. Because of this, I had to modify the transformer turns ratio from the original circuit, the output is 10turns instead of 20turns because of the additional voltage swing on the LMH6619 opamp output compared to the TL062 in the original. Good, because that lowers the output impedance even more. I salvaged the ferrite core from an SMPS (see another example in the snaps above). I cut off the isolation bobbin separator and basically wound the 10T winding on top of the 400T winding. Maybe 36SWG for primary and 28SWG (guesstimates) for secondary. You remove the metal retainer clip on the ferrite and then the core splits into two U shaped pieces, so can be removed from the bobbin for easy winding. This is a great example of a DIY electronics project that involves reusing electronic components and working with custom hardware setups—perfect for hobbyists and tinkerers. If you’re interested in electronic components and hardware, learn more.