Shutter Guard

This is the shutter guard circuit which has sensitive vibration sensor, piezo-sensor. This circuit is specifically designed for outlets to defend towards theft. It can recognize any mechanical or acoustic vibration in its area when somebody attempts to break the shutter and instantly turn on a lamp and sound an alert alarm. A 15-minute time delay right after switch-on makes it possible for adequate time for the outlet or shop owner to close the shutter.

The front end of the circuit carries a timer designed around the well-known binary counter IC CD4060 (IC1) to produce 15-minute time delay for the remaining circuitry to switch on. Resistors R3 and R4 and capacitor C2 will make Q9 output high right after 15 minutes. Diode D1 inhibits the clock input (pin 11) to maintain the output high till the electrical power is switched off. Blinking LED1 signifies the oscillation of IC1.

The high output from IC1 is utilized to enable reset pin 4 of IC2 so that it could function freely. Transistor T1 amplifies the piezo-sensor signal and triggers monostable IC2. The base of transistor T1 is biased working with a common piezo component that works as a small capacitor and flexes freely reacting to mechanical vibrations so that the output of IC2 is high up until the prefixed time period.

In the standby mode, the alarm circuit constructed close to IC3 stays inactive because it does not get current. Timing parts R8 and C6 produce the output of IC2 high for a period of three minutes.

When any mechanical vibration (generated by even a slight motion) affects the piezo component, trigger pin 2 of IC2 momentarily changes its condition and the output of IC2 is going high. This triggers triac 1 and the alarm circuit activates. Triac BT136 accomplishes the lamp circuit by activating its gate via resistor R9. IC UM3561 (IC4) produces a tone simulating the police siren with R11 as its oscillation controlling resistor. Zener diode ZD1 delivers stable 3.1V DC for the tone generating IC.

Construct this shutter guard circuit on a general purpose circuit board and enclose inside a appropriate, shockproof box. Connect the piezo component towards the circuit by utilizing a single-core shielded wire. Glue a circular rubber washer around the fine side of the piezo component and attach it on the shutter frame using the washer facing the frame to ensure that the piezo component is versatile to sense the vibrations. Attach the lamp and also the speaker on the outer side and the remaining components inside the box. Considering that triac is applied to the circuit, most points within the PCB will likely be at mains lethal potential. So it really is suggested not to touch any section of the circuit whilst trying out.