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Single chip microcomputer heart rate paper
LM393 can't replace 74 1, but can use LM358, which is also a common operational amplifier.

If you use STC single chip microcomputer, you can light it without triode drive, but it is a little dark.

It is best to add a resistor of about 1K to each I/O port to limit the current.

The reset circuit is not important. If you think there is something wrong with the reset, use something conductive and contact the reset needle with the positive electrode.

Fix the microcontroller first. If it doesn't light up, it must be a problem with the single chip microcomputer. Take a look at this program. If it doesn't light when there is no pulse, 0000 will be displayed. If it is 0000, it must be a problem with the single chip microcomputer. If it doesn't light up without a pulse, then leave it alone.

Connect a pull-down resistor, about 10K, to p3.5, and then connect a resistor, 1K, in series with the positive electrode to directly add a pulse to P3.5..

This is a trial-and-error method, first find out the problem and then solve it by elimination.