Although his plan is far from perfect, it can provide a preliminary idea.

To make a frequency meter, the basic structure is as follows:

(1) The front-end shaping circuit can limit and amplify the signal below the digital logic threshold to the standard TTL or CMOS or ECL level. The front end of the high frequency frequency meter should also have a prescaler. Simple hand training, this part can be given up temporarily.

(2) Reference clock and strobe signal. Count in the gating time, which determines the decimal point position. 2‰ accuracy, consider using a crystal oscillator as the local clock, and the clock can basically be debugged.

(3) Counter logic, various standard digital chips and decimal system are more convenient.

(4) Decoding and display circuit, equipped with various standard digital chips.

In principle, there are two loops: frequency counting and period counting. The high-frequency signal is the number of input signal pulses in the local gating time, and the frequency is directly obtained with an error of 1 bit; The low-frequency signal counts the number of local reference clocks in the period of the low-frequency signal to get the time value, and then converts the frequency.

Can be completed by single chip microcomputer, with timer and external counting function; It is best to use CPLD or FPGA with HDL language, which greatly simplifies the logic realization and circuit connection.