Now I am preparing a design to measure the frequency amplitude of a sine wave, using an 89s52 single-chip microcomputer. Because I haven't learned analogue circuits, it is a headache for waveform shaping and amplification. Now I plan to use the LM318 op-amp to amplify, and then use the Schmitt trigger to shape it into a square wave. The question is, what kind of amplifying circuit should be, and how to determine the magnification.
Thanks in advance!
I would suggest using something different, the LM318 needs a + and - power supply to operate properly. Also the output may not go low enough to drive a logic zero into the 89S52. I cannot tell you how much amplification you need or even if you need some as you did not specify the signal. What is the signal from, and what frequency will it be from max to min. Your link is intermittent, but for the short time I had it did not show all the necessary parameters or output swing. It is now showing a server error.
You might find this helpful: Using Operational Amplifiers in your Arduino project
Frequency and amplitude are two different things... And if you force it to a square wave you'll loose the amplitude information.
I'm not exactly sure what you're doing but MAYBE you want a comparator which is one of the EASIEST things to make with an op-amp. It gives you a digital high/low output so it also looses amplitude information.
Typically, you use a voltage divider (2 resistors) to get the threshold/reference voltage. And you can add feedback for hysteresis to make it "act like" a Schmitt trigger.
Note that op-amps usually need (or "like") positive & negative power supplies and that's often not shown on "example circuits". And, you have to "be careful" because most digital circuits don't like negative voltages (or voltages higher than Vcc).
In the absence of more information about your signal its not possible to give useful guidance.
What is the source of the signal?
How do you know its a sine wave?
What are the limits of its amplitude and frequency?