Then the second IC produces a mixed frequency from the output pin 3, this frequency is about 440 Hz – 550 Hz. Now, this frequency combines with the second IC’s frequency. Then, this output signal frequency gets into pin 5 of the second NE555 timer IC through the R8 resistor. this frequency value can be changed by R6, R7, and C3. In this mode, the timer IC produces a low signal frequency from the output pin 3, this frequency is about 1 Hz. In the police siren circuit, the first NE555 timer IC works in an astable multivibrator mode. Laser Security System with Police Siren Circuit Diagram Part 3 Then this transistor activates the police siren circuit. This high output goes to the BC547 transistor (T2) base terminal, so this transistor also turns on. Here we can change the Time Period by rotating the potentiometer knob. The formula of the Time Period calculation is T=1.1xRxC, where T is the Time Period, R is the potentiometer resistance value and C is the C1 capacitor. The output time period depends on the RV1 potentiometer and C1 capacitor. That’s why the IC output goes High for a fixed time. Here this NE555 timer IC work in monostable mode. Now the terminal 2 of the NE555 IC will be connected to the ground and this gets triggered. Laser Security System with Police Siren Circuit Diagram Part 2 When the output voltage of the IC gives to the base terminal of the transistor (T1), then the transistor is in turn on. Here the BC547 transistor (T1) works as a switch. This input voltage is less than the threshold voltage. So, there does not sufficient light on the LDR surface, then LDR gives low input voltage to the comparator IC. When someone crosses between the laser light and LDR. Laser Security System with Police Siren Circuit Diagram Part 1 Laser Security System with Police Siren Circuit Diagram Block Diagram Laser Security System with Police Siren Circuit Laser Security System with Police Siren Block Diagram Components Required Components Name The police siren generator circuit generates loud sounds like a police car using a speaker, it is the last and fourth part of the circuit. Using the time delay circuit we can set the time duration of sound-generating the police siren. This output change gives to the time delay circuit, it is the third part of this circuit. The light detector circuit output will be change when someone crosses between the laser light and the LDR. This laser light continuously falls on the LDR of the light detector circuit, it is the second part of this circuit. In the first part has a laser pointer, it is the main source of light in this project, which can emit light output of less than 1 mW power. This project looks very complicated but it is divided into four simple parts.
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