Automatically set timer

Shown is an automatically set timer . This is a monostable multivibrator circuit that pulses reliably when powered on
. Once the power is turned on, capacitor 02 needs a certain amount of charging time, so the potential of pin ② at the trigger input terminal of NE555 can generally be
below 1.3 Vcc, causing NE555 to generate output pulses . Then, because the power supply vcc charges C2 through R2 and VDI, the potential on C2 gradually approaches
vcc, and VD1 is reverse biased to act as an isolation.