Development of Counter Based Digital Capacitance Meter Implementation using Synchronized Relaxation Oscillator

Abstract

A digital capacitance meter is a piece of electronic test equipment used to measure capacitance mostly of discrete capacitors. This project presents the design and implementation of asynchronous digital capacitance meter using the principle that when a capacitor is connected across a constant DC source, it charges at an exponential rate which is dependent on the capacitance of the capacitor seen by the source as well as the resistance seen by the capacitor in the circuit. In this research, an unknown capacitor whose capacitance is to be determined was used in the timing circuit of a 555-timer base monostable (One-shot) multivibrator to give out a single pulse whose ON duration is a function of the capacitor. This pulse was synchronized to a reference clock of frequency 7.2kHz using a positive edge-triggered D flip-flop to give a count enable signal to a decade counter and ensure that the count is stopped whenever it reaches the capacitance of the capacitor used in the timing circuit. The device was tested on different capacitors (both electrolytic and ceramic) and the results of the capacitance measurement show that the device was able to measure capacitors precisely within their dynamic range of values.