Schmitt trigger is only suitable for signals with appropriate levels, but not for small or large signals. Hysteresis comparator circuit is recommended, which is similar to Schmidt trigger in principle, but the applicable input range is much wider and adjustable. The circuit is as follows:

When using dual power supply:

When ui >；; Output low level (-VCC) when VCC * r1(RF+r1);

When the user interface

When -VCC * r 1/(RF+r 1)

When using a single power supply, the grounding of R 1 can be changed to VCC/2, and the voltage of VCC/2 can be obtained through two voltage dividing resistors whose resistance is much smaller than R 1.