Brief 555 Schmitt trigger logic inverter

Schmitt triggers are voltage comparators that have 2 threshold voltages that cause the output to change state. The middle ground voltages (hysteresis) keep the output in the last state that it was put into.

Digital Inverters give a high output when the input is low. Whereas the output goes low when the input is high. They are called NOT gates in digital electronics.

Don’t confuse a digital inverter with a  power inverter takes in DC (usually from a battery) and outputs alternating current, usually at 120V.

Schmitt trigger hysteresis graph diagram by Electronzap Electronzapdotcom
Schmitt trigger hysteresis graph diagram by Electronzap Electronzapdotcom

The hysteresis of a schmitt trigger circuit prevents rapid repeated switching if the signal voltage is bouncing back and forth a tiny bit.

Brief circuit schematics with short video – List of pages

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Diagram:

Simple 555 timer Schmitt trigger logic inverter circuit schematic diagram by electronzap electronzapdotcom
Simple 555 timer Schmitt trigger logic inverter circuit schematic diagram by electronzap electronzapdotcom

Diagram is explained in the video below.

  • When pin 2 (trigger) has less than 1/3 supply voltage to it, the output goes high.
  • When pin 6 (threshold) gets more than 2/3 supply voltage, the output goes low.
  • From 1/3 to 2/3 supply voltage, the output stays in whatever state it was last put into. That’s the hysteresis range when using a 555 timer as a schmitt trigger.

Video:

Quick 555 timer based schmitt trigger inverting logic switch circuit schematic diagram to breadboard

555 timer pin layout:

555 timer pin layout illustrative diagram by electronzap electronzapdotcom
555 timer pin layout illustrative diagram by electronzap electronzapdotcom
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