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PC-based frequency counter schematic Introduction

2017-08-15 17:12  
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This article is a PC-based frequency counter schematic profile. The principle is simple but effective. For you to more effectively grasp this principle, we recommend that you read the text combines schematic. It follows the basic method of measuring low-frequency, i.e. at a low frequency, duty cycle and frequency of measurement to calculate the full-wave period measured. Cascaded binary counter signal for low frequency signals. Parallel port on the computer is used for data entry from a binary counter. This data is used to measure time, and frequency of the signal. The block diagram shows the basic connections and digital counter 25-pin parallel port pin "D"  connector  of the PC (control register 379 Hex is used to input). External hardware required for the high frequency signal into a low frequency signal. Therefore, the main role is played by the frequency measurement software. Computer-generated time interrupt frequency 18.21 Hz, ie every 54.92 milliseconds. Software uses this time interrupt as a time reference. Control PC's parallel port register reads and data are stored in an array using a loop for approximately 54.9 ms. This stored data is to analyze the bit operations. Initially, the high-order bit (most significant bit and seventh) of each array element is to scan the existence of a complete square wave. If it is found, it is a measure of the time and if not then the second (sixth place) is scanned. This operation is performed to the third place, if not completely square waves are still found, generate an error message is displayed, or there is an error in reading or frequency signals below 19 Hz. Low three control registers are not used to. When the wave is found, along with its time, frequency component, the measurement accuracy is calculated and displayed in percentage. Number of data taken at 54.9 ms are also shown. As mentioned above, the starting point is the lower range of about 19 Hz. Data read is about 54.9 Ms. Accordingly, the frequency as low as possible, can be measured 1 /. 0549 Hz. Lower range depends only on the sampling time is fixed at 19 Hz is almost (18.2 Hz, accuracy). The range depends on many factors, such as the Department of Defense counter value and operating frequency range of the counter IC. If the MOD N counter (where N is an integer), the upper limit (UL) The frequency of UL = 19 xn5 Hz. So for Defense 16 counters UL @ 20 MHz, Defense 10 counters MHz. Care must be taken to ensure that this limit operating frequency range of the counter IC used. Precision measurement is a machine-dependent parameters. High-speed machine will have better accuracy than others. Basically, the accuracy depends directly on the amount of data read into a standard time. Precise measurements of the MOD is inversely proportional counter. High accuracy when the Department of Defense 10 Defense 16 counters can be used instead of the counter, but this will limit the maximum frequency measurements, and vice versa. This is a simple technique to measure the frequency in a wide frequency range and acceptable accuracy limits using a computer. If you are reading this first principle, the proposed Duokanjibian, grasp this principle.

PC based Frequency Meter

PC based Frequency Meter

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