Cheap Inductor Measuring Instrument Composed of Single IC ----- 74HC04 L Meter

Cheap Inductor Measuring Instrument made of single IC, 74HC04 L Meter Keywords: 74HC04, inductor test circuit Be Author: Zhuang Yizhen This design instance. It shows how to build a reliable low-cost, simple inductor measuring instrument. The foundation of the inductor measuring instrument is a Pierce CMOS buffer oscillator drawing). Instead of ordinary quartz crystals, connect to the inductance. Such an oscillator uses a simple CMOS inverter biased by a resistor R1 therewith in its linear region to form a high gain inverted amplifier. Due to this high gain, the inverter is lower than the power consumption of the unbuffered door, even if a smaller signal, the driving output is high and low levels. The LC network constitutes a parallel resonator. Its resonant frequency fO = 1 / 2π√LXCs. This frequency corresponds to period T0, where CS = C1 || C2 = 50nf. Therefore, the resonant frequency f0 or period T0 can be measured to calculate the inductance Lx. On the resonant frequency, the LC network provides a 180 ° phase shift from the input to the output. The phase shift of the oscillator's oscillating circuit F0 must be 360 ​​°. And the gain of the oscillating circuit must be greater than 1, so that oscillation can be generated. The inverter provides an additional 180 ° phase shift from the input to the output and a high gain to compensate for the attenuation of the network. The resistor R1 has a value of 1 MΩ ~ 10mΩ. The resistor R2 isolates the output of the LC network IC1A. A clean square wave can be obtained from the gate output. In addition, the phase offset of the resonant frequency can also be increased by R2 to improve the frequency stability. In order to achieve the best performance. A low-sensitive film capacitor can be used, such as Vishay MKP1837 polypropylene film capacitor series, accuracy up to 1%. A thin film capacitor for standard tolerance can be used, and capacitance can be selected to achieve optimum accuracy with a precision capacitance tester. The circuit is low power consumption, and the battery can be used as a power source.

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