555 monostable mode

*In this circuit, when the trigger pin (TRI) voltage drops quickly below VCC/3, the internal flip-flop SR is reset; *Then, the 555 output changes to high level and the capacitor charge happens; *When the capacitor voltage reaches (2/3)*VCC, the internal flip-flop SR is set; *Then, the 555 output returns to low level and the capacitor discharges almost instantly; *The 555 output remains in low level until another low level pulse occurs at the trigger pin; *The pulse width (W) depends on how long it takes the capacitor to reach a voltage equal to (2/3)*VCC; -> W = 1.1*RC