Thank you for sharing your excellent circuit and code. I made a PCB from your circuit image and used 2n2222 & 2N2907 transistors and 1% resistors. I didn’t have a non-polar cap, so I soldered the anodes of two 100uF caps together. As a test, I tried adding parallel diodes to the caps, but found they made no difference in my readings. On a pair of used 2200uF 10V caps I got 0.0 Ohms on one that looks good, and 5.600 Ohms on one with a slight top bulge, so it finds bad caps.
The problem I am having is that I am unable to calibrate it. Using a one Ohm resistor I had to set “double current = 0.007460;” to get the meter to read 1.012, but then a 1/3 Ohm resistor reads .090. Could the transistors or DIY capacitor cause this? I'm a beginner, so your post was highly educational and I got a new test tool as well! Thanks again.
Ron