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The roadblocks flashing alarm circuit ( 4 )

2017-01-06 03:59  
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The roadblocks flashing alarm circuit ( 4 )
Road blocks flashing warning light using battery is shown in the figure, and it can be used local road facilities without AC power for roadblocks alarm. NE555, RP1 , RP2 , C1 , RL and RL form a a light -controlled self-excited multivibrator. Due to light exposure in daytime, it is in low resistance, NE555 forces reset terminal ④ feet level to be less than 0.4V, and the NE555 is mandatory reset, output end ③ feet is constant low, then VT1 and VT2 are cutoff, warning lights E does not shine. Due to RL has no light exposure in nighttime, it shows a high resistance, then it is divided by RP2 to make ④ feet level increase, when it is greater than 0.4V, you can lift the blockade on the circuit, the circuit is start-up.