In current times, it is necessary to have some security at home. To avoid acts of vandalism and thefts, we need instant responsive security alarms that are active all the time. This circuit is very helpful at this situation. We have a smart security alarm which can be used in home, in your locker or in cash box guard that thwarts the theft attempt by activating an emergency alarm.
The security alarm circuit is built around the CD4060 and few more components. IC CD4060 is 14 stage ripple carry binary counter, divider and an oscillator. Its built in oscillator is main feature of this IC that’s why it can be used in numerous application like flasher, clock generator in timer circuits.
Fig. 1: Prototype Of CD 4060 Based Security Alarm On Breadboard
IC1 is working as frequency dividing circuit. Its inbuilt oscillator is based on three inverters. The basic frequency of the internal oscillator is determined by the value of the capacitor connected to its pin 9 and the resistor connected to pin 10. By increasing or decreasing the value of capacitor and resistor we can change the time delay for the period of on and off. Internally the oscillator signal is applied to the first bistable which drives the second bistable and so on. Since each bistable divides its input signal by two, a total of fifteen signals are available, each of half the frequency of the previous one. Output Qn is the nth stage of the counter, representing 2n, for example Q4 is 24 = 16 (1/16 of clock frequency) and Q14 is 214 = 16384 (1/16384 of clock frequency). Note that Q1-3 and Q11 are not available
In day time reset pin 12 of IC1 remains low, so oscillation build around IC1 is enabled. Similarly in darkness, reset pin goes high which resets the counter making its output low as a result it stop the oscillation of the internal oscillator.
If the circuit is kept in darkness, the light dependent resistor resets the IC and it stops oscillating. Pin 4 and 5 of IC1 go low, so, result buzzer and relay connected at output will not sound means your locker or cash box is safe.
If somebody tries to open or enter into the restricted area, he will be carrying a torch or some other source of light. Light from this source will fall on LDR making pin 12 go low and IC1 starts oscillating and counting. Therefore after the preset time set with the help of pin 9, 10, 11 output at pin 4 goes high after few seconds. Therefore pin 4 of IC1 goes high for two seconds after the door is opened and goes low for another two second. As a result, buzzer sounds for two seconds and remains off for another two seconds and this cycle of on and off is repeated until you close the light falling on LDR stops.
We have also connected a relay at pin 4 so that you can also connect an external buzzer or a LED. So when buzzer is not sounding you will get indication through the buzzer attached through relay and more advantage is that you can also connect an AC operated bell through it. This can be done by connecting a transistor with the help of resistor. Also check the Luggage Security Alarm Circuit