I wanted to design a simple ohmmeter for my electronic test bench instead of using a multimeter. I just needed to quickly measure new and used resistors to sort them for bin storage or to match known values. The accuracy would not be important as long as I could guess a standard value, as I quickly tested them.
Then I came across Mirko Pavleski's Nano unit plus Simple Circuit project https://simple-circuit.com/arduino-auto-ranging-ohmmeter-lcd/ These were just what I was looking for.
However, after I built the prototype, a problem showed up while testing known resistor values. It worked accurately enough to sort resistors from 10 ohms to 1+ Meg ohms, but for some reason did not work between 120k-190k ohms range?? 100k and 220k read fine. I double checked all the calibration resistor values and wiring and found no issues?
However, this problem was resolved on the Arduino Forum by user BOFFIN. Many thanks to him! https://forum.arduino.cc/t/auto-ranging-ohmmeter-does-not-read-150k-ohm-solved/880215
After changing the 2MΩ resistor to 1MΩ and the constant table from 2000000ul to 1000000ul in the program the unit performed A-OK
I settled on building with a small case with Oled display and bolt terminals. The meters accuracy