Digital counting circuit

Figure 28. Digital counting circuit with drive circuit 1907 and liquid crystal display, a to k Face electrodes 1 Back electrode...

A block diagram of a counting circuit arranged for time interval measurements is shown in Figure 25.5. Individual digital circuits will not be discussed... 

While the frequency of a signal can be established using an oscilloscope, the accuracy specification for most oscilloscope time bases gives a tolerance figure of 5%. For mai situations this is totally inadequate, as a more precise measurement is required. Fortunately, a sinusoidal wave can easily be converted into a pulse or square wave, which can then be counted by digital electronic circuits. With electronic counting techniques, the frequency of a signal can be determined with a very small tolerance. 

Fig. 3. Scientist Donald L. Miller holds an integrated circuit chip comprising a high-resolution superconducting analog-to-digital converter. The one-square-cen timeter chip, known as a counting converter, holds promise as an unprecedented combination of high resolution and low power consumption, as needed in future air traffic control radar and infrared space-tracking applications. The 12-bit circuit (Josephson junction) has a resolution of 1 part in 40CK). (Westinghouse Electric Corporation)...

With the advent of inexpensive, fast frequency counters, which count the individual cycles over a precisely fixed period (usually 1 s) and display the frequency digitally, it is more convenient to connect the radio-frequency output of the variable-frequency oscillator directly to the frequency counter and determine the total capacitance with the aid of Eq. (27). This technique is highly suitable for the present experiment if a WTW Dipol-meter or another LC oscillator is available or can be constructed. (With the Dipolmeter only the variable-frequency oscillator is used.) A simple LC oscillator circuit that can be constructed from inexpensive components has been described by Bonilla and Vassos this circuit, with a small modification to provide for one side of the tank to be grounded, is shown in Fig. 2. In this circuit, as in the WTW Dipolmeter circuit, all tank capacitances are in parallel. [This is not true of the circuit described in Ref. 4 of Exp. 30, as that circuit incorporates some series capacitance. If that circuit is employed, Eqs. (28) to (30) are not valid and Eqs. (30-3) to (30-5) must be used instead, unless the null mode is employed.]... 

The data reduction task may be eased further by replacement of the raster pattern oscilloscope with 10 MHz counters. The advent of integrated circuits has lowered the cost of counting systems drastically. The total cost of the kits to build the 10 MHz oscillator [4], gates [5], and counters [6] shown in Fig. 3 is less than U.S. 200. The number display is 3 digits which means that a maximum of 199.9 /jsec may be recorded by any one counter before overflow. 

Figure 4.1.3. The TWmeter [McClure, 2002 4049] a hand-held NIR spectrometer (A) that consisting of three unflltered NIR-emitting diodes, a silicon-V/F detector and a minimum-featured microprocessor (B) for determining chlorophyll and moisture. (C) complete circuit that controls to meter functions. Cost reductions were achieved by letting the microprocessor count the output of the V/F converter, thus avoiding the need for an external analog-to-digital converter.

The flip-flop circuit described previously is the basic digital counter and makes wide use of CMOS technology in applications such as digital watches where current drain must be held to a minimum. A quartz oscillator provides the basic clock whose pulses are repeatedly divided by two by a series of flip-flop circuits in order to count seconds, minutes, and hours. 

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