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Sunday, April 12, 2015

Quick and dirty way to measure inductance and capacitance with an arduino uno or any other micros

Measuring inductance and capacitance are not among the commonly available options in a simple multi-meter.  But often we need to measure an unknown capacitor or a hand made coil, for e.g while building oscillators and filters for qrp (radio transmitter) projects. Here is a collection of simple techniques which can be used to accurately (all-most as good as expensive tools) measure the values for hf (high frequency)  applications. But i am not going to talk about a net work analyzer here. This is a very quick and dirty one based on arduino uno.

A small rf coil (2.5-3.5micro henry)

Measuring Capacitance

This is the easiest and you can measure capacitance from 1pf to 100 micro farad by using just an ardiuno uno. The details of the project and the principle of the measurement technique are explained by Jon in his page here. It doesnt use any additional hardware, just upload the arduino sketch (which can be found here or here) and place the unknown capacitor to the analogue pin A0 and A2 of the arduino, and just read the capacitance value! Even without any calibration, it gave me accurate results :)

So the set up is as shown in figure:

Measuring Capacitance with an arduino uno

Measuring Inductance

To measure inductance we need some more componets from the junkbox. I just hooked them up on a breadboard and it worked like a charm! The concept is explained by Kerry (here). I didnt have a comparator as he used, so i used LM319 which has a slightly different pin out (Be careful as my chip heated up with a wrong connection by thinking it as LM339!)

Schematic for inductance measurement
In this case, the unknown inductor forms an lc circuit together with a 0.01 micro-farad capacitor which forms a resonance frequency, for e.g with 2 micro henry, it will resonate around 1.12 mega hertz ( A good online calculator here) and the frequency  can be measured  by  arduino uno with a frequency counter library which can be downloaded here. After installing the library by unzipping to arduino / library folder, just restart the software. Now there will be a serial example which can be loaded in to the arduino and open the serial console to read the frequency. This works fine up to 8 MHZ. The measurement is from the Digital pin 5 of the uno.

Here i used the online calculate described above to calculate the inductance from frequency and capacitance value (0.01 micro farad). It is possible to improve it for direct read out and can read more about it on Kerrys pages.

Here is my simple hookups on a breadboard and it worked!! Ideally it can be constructed on a copper-clad in a Manhattan style.

Inductance measurement

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