555 Timer in Monostable Mode

A single timed pulse on demand.

In monostable mode the 555 rests with the output low. A brief low pulse on the trigger pin starts the output high while the capacitor charges through one resistor. When it reaches two thirds of the supply, the output drops low again and waits.

The pulse length depends only on the resistor and capacitor. With 100 kΩ and 10 µF it is about 1.1 seconds. Keep the trigger pulse shorter than the output pulse, or the output will stay high.

• Useful for debouncing and delays.
• Pulse length is set by one R and one C.
• Use a stable capacitor for accurate timing.

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