HOW IT WORKS
The heart of the circuit is the buffer colpitts oscillator(the first stage) which resonates with the unknown inductance to give a Sine wave of a particular frequency .
The frequency of the sine wave is a function of the unknown inductance and the four 1000pF capacitors.
The output sine wave is amplified by the second transistor and is then rectified by the capacitor and diode combination that Follows.
The rectified sine wave now having only positive excursions is buffered by the third transistor and is then fed to the 74ls393
Counter ic which is configured as a divide by 256 counter.
The output of the ic pin 6 and ground is connected to the frequency meter.

NOTES
The 7805 regulator powers the IC and the last 2 transistors
The circuit operates from a 9V battery which also feeds the regulator
The Ic consists of two counters in one package of 14 pins hence you need just one.
PIN 14 is VCC and PIN 7 is ground
The ic is TTl IC

PERFORMANCE AND GETTING YOUR READING
My own digital meter can read frequency so I use it to take the reading.
I programmed my calculator to get me the inductance value from the reading. A simple computer programme can do this as well.
Actual frequency= Frequency reading*256 (the counters have scaled down the frequency by 256 times)

Actual frequency = f=

So the last equation allows you to solve for the value of the inductance Lx which will be in microhenries.

Sorry the equations don’t look too neat I hope you get them though.
Any comments about this circuit can be mailed to me and I hope somebody finds it interesting enough to construct And possibly make a stand alone unit with microprocessors or PICS and displays that I haven’t got. Thanks to Bernardo Dimacali for helping me put the equation in a good and clear form.
lm7805中文資料? http://www.nxhydt.com/soft/78/223/2008/200805053492.html