The LM555 timer acts as a “one-shot” pulse generator. The pulse begins when the LM555 timer receives a signal at the trigger input that falls below ⅓ of the voltage supply. The width of the output pulse is determined by the time constant of an RC network. The output pulse ends when the voltage on the capacitor equals ⅔ of the supply voltage. The output pulse width can be extended or shortened depending on the application by adjusting the R and C values.
- Texas Instruments LM555 Timer Data Sheet
