Switch NOT logic gate – digital signal inverter

Mechanical switches can be used in a way where when the switch is off, the output or load will be on. Whereas when the switch is on, then the output or load will be off.

If you really need a NOT gate, there’s almost always better semiconductor versions. But the mechanical version makes it easier to understand the NOT gate, so it’s a fun circuit to learn.

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NOT truth table/schematic symbol

NOT gate schematic symbol truth table diagram by electronzap electronzapdotcom
NOT gate schematic symbol truth table diagram by electronzap electronzapdotcom

Switch NOT gate circuit

Switch NOT gate deminstration circuit demonstration schematic diagram by electronzap electronzapdotcom
Switch NOT gate deminstration circuit demonstration schematic diagram by electronzap electronzapdotcom

When the switch is off (open), the current flows through resistor and our output load, the LED. When switch is closed (on), it makes it so both sides of the LED are connected directly to ground. Therefore no current flows through the LED and it is off.

  • Switch on = LED off
  • Switch off = LED on

Current is always flowing through the protective resistor, in fact more current is flowing while the switch is closed, and the LED is off than when the LED is on.

Current path visualization

Switch based NOT logic gate illustrated by electronzap electronzapdotcom
Switch based NOT logic gate illustrated by electronzap electronzapdotcom
Video

Electronics course 10 NOT gate signal inverter using switch NPN BJT and 7414 74HC14 hex IC

Basic electronics circuit fragments and simple circuits 8 NOT logic gate signal inverter diagram by electronzap electronzapdotcom
Basic electronics circuit fragments and simple circuits 8 NOT logic gate signal inverter diagram by electronzap electronzapdotcom
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