Inductance adapter for frequency meter

Posted on Oct 1, 2012

The following circuit enables me to measure inductance of the inductor labeled LX which is the inductance to be measured. The o/p of the circuit is a TTL square wave whose frequency relates to the inductance being measured. 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.

Inductance adapter for frequency meter
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The output of the ic pin 6 and ground is connected to the frequency meter. The inductance meter adapter output is connected to a frequency meter and the inductance is calculated from the frequency.Hence you need a frequency meter and some calculation to get your inductor value. All resistances are in ohms. 7805 positive regulator 5v o/p. 2SC9018 is a high frequency transistor with FT of 1.1 Ghz . you need high frequency transistors in the circuit where it is used in case you want to substitute for it. I guess 2n2857, 2n5179 ,BF180 can be substituted. 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

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