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we demonstrated a while ago that you can build a LC/LCF meter out of a mcu.
that meter works out in the digital domain. How about an analog LC or LCF meter?
here is one.
it essentially relies on a frequency source to charge up or down an inductor / capacitor. Once the voltage on the inductor / capacitor reaches the schmitt trigger's threshold voltage, the NAND gate flips, making its output a PWM signal. That PWM signal is further bufferred and ran through a low-pass filter so the output voltage on C1 is dependent on the duty cycle of the PWM signal, which itself is dependent on the value of the inductor / capacitor.
the clock source is a simple NAND gate + a resistor / potentiometer + 1 capacitor.
you do need standard inductors / capacitors of known value to calibrate the meter.
enjoy.
(原文件名:Analog LC Meter.PNG) |
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