This circuit is a Schmitt trigger, a type of comparator, built for some reason using a 555 timer chip. It measures the input to see whether it is above or below a certain threshold. The threshold changes in order to reduce the chance of the output switching back and forth quickly due to a noisy input near the threshold. This circuit takes advantage of the fact that the 555 output goes high when the trigger input drops below 1/3 V in, and the output goes low when the threshold input exceeds 2/3 V in.
This page is a utility for simulating триггер шмитта (инвертирующий) на чипе 555 online with specified initial values.









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