In this work, STC 12C5A60S2 is used as the main control chip, and based on this, diode 1N58 19 is used to realize half-wave rectification, and 10 bit AD in single chip microcomputer is used to sample the rectified input signal to realize peak detection. At the same time, the input signal is amplified by operational amplifier LM837, and then the original signal is shaped into a standard pulse waveform that can be recognized by single chip microcomputer by Schmidt trigger, and then the frequency is measured by internal counter (timer); In this way, rectification and AD sampling can detect the peak value of the input signal. The frequency of the input signal is detected by amplification and shaping.

Two. Basic function and technical index requirements

(1) input AC voltage: 1mv ~ 50v, divided into five grades:

① 1mV~20mV，② 20mV~200mV，③ 200mV~2V，④ 2V~20V，⑤ 20v~50V .

(2) sinusoidal frequency; 1Hz ~ 100 khz；

(3) Detection error: ≤ 2%;

(4) It has a detection start button and a detection stop button. Press the start button to start detection, and press the stop button to stop detection;

(5) Display mode: Digitally displaying the validity of the current detection means displaying the last detected valid value when the detection is stopped;

(6) Display: LCD, the display resolution is 0.1%of the full scale of each gear;