A Simple One-MHz Frequency Counter

摘要

If you work with digital or analog oscillators, at some point you will want to double-check their operating frequency. Analog oscilloscopes will only get you within a half-order of magnitude or so; a good frequency counter will take you the rest of the way. In this article, I will show you how to build a simple frequency counter, like the one shown schematically in Figures 1A and 1B. It has a response range from 1 Hz to 1 MHz, a resolution of 1 Hz, and a typical sensitivity of +-250 mV or less. The maximum input voltage is 30 VAC (using a 10X scope probe). This provides an accuracy of +-30 PPM at +-1Hz, with a supply voltage of 12 V @ 200 mA. The circuit is composed of an input amplifier, power supplies, reference clock, and eight-digit counter. I will explain the operation of each one in the following sections.