Use NE555 to make light-controlled flashing warning lights

VDI, VD2, C3, and C4 form a simple capacitor step-down half-wave rectifier and voltage stabilizing circuit. After powering on, the two ends of C3 can output
a DC voltage of about 12V to provide power for the time base circuit. Time base circuit A, RP1, RP2, CI, and RG form a light-controlled self
-excited multivibrator. During the day, RG is exposed to light and has low resistance. The level of pin 4 of the time base circuit is less than 0.4V, and A is forced
to reset. Pin 3 of the output terminal is always at low power level, vs has no trigger voltage and is in the off state, and the light H does not light up. At night, RG has high resistance without light exposure
. Its voltage division with RP2 causes the level of pin 4 of the time base circuit to increase and is greater than 0.4V. Thus, the blockade of the time base
circuit is released, and the circuit starts to oscillate. The starting principle is: set pin 2 of A to low level, then A is set, and pin 3
outputs high level. =The I pin charges the capacitor CI through RP1, causing the voltage at both ends of CI, that is, the level of the 6th pin of A, to continue to rise.
When it rises to 2/3 of the power supply voltage, A resets, and pin 3 outputs a low level. At this time, C1 Discharge to pin 3 through RPI, causing
the voltage at both ends of CI, that is, the level of pin 2 of A, to continue to drop. When it drops to 1/3 of the power supply voltage. A is set again, pin 3 suddenly changes to high
level, and charges CI through RP1..., and oscillation occurs over and over again. The gap between pin 3 outputs high level and low level
. When pin 3 outputs high level, vs can obtain the trigger current through Rl and turn on. The light H is lit: when pin 3 outputs low level
, vs loses triggering. The current is turned off when the alternating current crosses zero, and the lamp H goes out. It can be seen from the above analysis that as the oscillation of the time base circuit occurs, the warning light H flashes continuously.     The potentiometer RPI is used to adjust the flashing frequency of the lamp H, and RP2 is used to adjust the light control sensitivity of the circuit so that the circuit can work normally under appropriate illumination. The incandescent lamp H in this circuit works in a half-wave undervoltage state. Although it flashes and glows, its service life is quite long.