Here a simplest yet quite accurate inductance meter is presented, which can be built within few minutes. Furthermore, the circuit can be powered-up with a single 1.5V cell. However, a frequency meter would be required to work-out the inductance.

Designed and Presented by: Abu-Hafss 

Using Cross-Coupled NPN BJTs

The circuit is pretty straight forward wherein, two NPN transistors are cross-coupled to form a flip-flop oscillator. The values of R1 and R2 could be anything between 47 - 100R. The frequency of the oscillation is inversely proportional to the inductance and it can be calculated with the following formula:

Frequency (kHz) = 50,000 / Inductance (uH)


Initially the circuit has to be calibrated using a known inductor, as described below:

Suppose, we have an inductor of 100uH. Putting the value of inductor (100uH) in the above formula, we get 500kHz.

Connect the inductor cross point A & B and power on the circuit. It will start oscillating.
Connect the frequency meter at point A or B and ground.
Adjust the POT until the meter reads 500kHz. Now the circuit is calibrated.


Connect an unknown inductor across A & B.
Power on the circuit and read the frequency at point A or B.

The above formula can also be written as:

Inductance (uH) = 50, 000 / Frequency (kHz)

Putting the value of frequency in this formula, the value of the inductor can be found.


Waveform Image:


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