Photoelectric flashing light circuit

When road construction is carried out at night, red warning lights are usually set up and turned on at the construction site to ensure the safety of pedestrians and vehicles.
The warning light control circuit introduced in this section has two functions: light control and flashing. At night, the circuit can control the warning light to automatically turn on and make it
work in a flashing state, and it can automatically turn off during the day.
    The working principle is as follows: The circuit is shown in Figure 9-23. This circuit uses the "NE555" integrated circuit chip and related peripheral components to form
a typical indirect feedback controllable ultra-low frequency oscillator. Its oscillation frequency is, =l . 443/[(RRPl +ZR2)c3. ], whether it works or not
is controlled by the potential of its ④ pin. The photoresistor and R3 together form a light control circuit to realize automatic detection of ambient light and control
the ④ pin potential of IC1. The output of IC1 directly controls the on and off of the thyristor vs. VTH directly controls
the on and off of the warning lighting through the socket. Ci, VD1, VD2, G and other components constitute a typical capacitor step-down power supply circuit. It can provide
1ZV DC working power supply for the control circuit .
    During the day, due to the bright ambient light, Re is exposed to light and has a small resistance. After dividing the voltage with Shu, the voltage at both ends of Rc is low (close to ov), so
that the ④ pin of IC1 is clamped to a low level and oscillates at ultra-low frequency. The device stops oscillating, and the output of pin ③ of IC1 is low at this time. VTH is blocked, the warning light does not
light up, and the circuit is in a static state.
    When night falls, as the light irradiating Re gradually decreases, its resistance gradually reaches the maximum (about 2Mn). After the voltage is divided
, the potential of the ④ pin of IC1 gradually reaches a high potential (about lov ), the ultra-low frequency oscillator starts to vibrate, and the potential of the output terminal of pin ③ begins to
change periodically between high and low. When its output is high potential, VTH is turned on and the light is on; when its output is low potential, VTH is blocked and the light is off.
In this way, the warning light is controlled by the ultra-low frequency oscillator and works in a flashing state. The function of automatically flashing the warning light at night. Adjusting
RP1 can change the frequency of the ultra-low frequency oscillator, and also change the frequency of the automatic flashing of the warning light. When the sky gradually gets brighter, as
the light irradiating Rc increases, the resistance of R gradually changes to the minimum (about 10kn), then the oscillator stops vibrating, and the ③ pin of ICI resumes the output
to low potential. , VTH is blocked, the warning light does not light up, and the circuit returns to a static state. Based on this principle, the circuit
will automatically work in cycles according to the control of ambient light .