Roadblock flashing warning light circuit (1)

Roadblock flashing warning lights are mainly used for warning indications in construction sites and dangerous areas. It has an automatic function of light
. During the day, the lights are on. When night falls, it can drive the red warning lights to flash to serve as warning indications.
For use, its circuit is shown in Figure 2 9l.
    The power is independent of the integrated circuit
TWH8751 and RP, R. ,
f. It forms an ultra-low frequency oscillator
whose oscillation frequency can
be adjusted through RP. Phototransistor
VTP and R. It forms a light control circuit
. During the day, VTP is exposed to light
and shows low power.
The ② pin of the strobe terminal of TWH 8 778 is
high level (≥1.6V), and its
internal Darlington tube is cut off. The ④ pin outputs high level. Relay K does not act, its moving contact kl is open, and the warning
light E does not light up. When night falls, the resistance of VTP gradually increases as the light weakens, so
the level of pin ② of IWH8778 drops. When it drops to 12V or less. The oscillator composed of TWH8778 starts to vibrate, and
the ④ pin alternately outputs high level and low level . The relay K is activated and released, and the light F flashes.
Adjust RP to change the flash frequency of the light. By changing the resistance of R, you can adjust the light control sensitivity of the circuit.
    K can use JZC-221:, I)C12V small medium power electromagnetic relay, the contact capacity can reach 5-7A. T
adopts 220V, +12V, SVA small and high-quality power transformer, which requires long-term power supply without generating heat. G is a 12V
battery. When the AC power grid is out of power, G can supply power to the circuit through VD:) . RL is M (; 4j type and other photosensitive
resistors. It is required that the difference between light resistance and dark resistance is as large as possible. During installation, it is required that the site RI is allowed to feel
outdoor natural light, fi/l < the warning light E itself illumination of light