We all know that the most troublesome components in electronics are inductors and capacitors. Usual ones have high tolerance, time has an effect on them and their cost can be quite big. Besides that, i believe there are other people like me, who have boxes full of salvaged components from things that couldn’t be repaired. Now, from those components, you can measure capacitors and inductors with the tool presented in this project.
The L/C meter presented has a pretty good accuracy, +/- 1% of reading +/- 0.1pF or +/- 10nH. The measurement method is not the usual one but it’s very interesting, first the microcontroller measures the frequency of the oscillator, then measures the frequency of the oscillator with an added known capacitor and last time it measures the frequency of oscillation with the unknown component added.
In my opinion this method is a good approach if you can measure the frequency accurately. If we look at the equations described in the project that gives us the value of the unknown component we observe it only depends on those three frequencies and the value of the added capacitor. So we have only one element in our equation that isn’t measured, Ccal which can be chosen to be a higher quality capacitor with low tolerance and thus each time you calibrate the meter the frequencies are measured again and the calculations will be more accurate in case some component from the oscillator changed its value a bit because of temperature for example.
Another good function it that it can show you the difference between two components, very useful for matching. The oscillator is done using a LM311 comparator with the resonant circuit in the positive feedback loop. The microcontroller used is a PIC16F84, the assembler code is available as well as the hex files and schematic.
Inductance/Capacitance Digital Meter: [Link]