In this project we will design a smart security alarm circuit which will detect and create unwanted activity and alert us using a buzzer. In this project we will design the circuit from the prospective of securing the bikes. So, here unwanted activity is shocks. To detect the shocks we can use piezoelectric disk. For those who don’t know about piezoelectric disks, it creates voltage when it is being hit. Although this voltage is not enough to work with it at logic level, so we have to amplify this voltage using differential op-amp.
The differential op-amp shown above has an amplification factor of 30. This amplified signal then gets compared to a reference voltage using a comparator. This will give us a signal, when bike is moved.
Then this signal is sent to a D type flip flop. We will use CD4013B IC which is dual D type flip flop IC.
Introduction to CD4013B
The CD4013B dual D-type flip-flop is a monolithic complementary MOS (CMOS) integrated circuit made with N- and P-channel enhancement mode transistors. Each flip-flop has independent data, set, reset, and clock inputs and “Q” and “inverted Q” outputs. This IC can be used for shift register applications, and by connecting “inverted Q” output to the data input, for counter and toggle applications. The logic level available at the “D” input is transferred to the Q output during the positive-going transition of the clock pulse. Setting and resetting is independent of the clock and is accomplished by a high level on the set or reset line respectively.
Applications of CD4013B
- Data terminals
- Alarm system
- Industrial electronics
- Remote metering
Circuit for smart security alarm
To create this circuit we need following components.
- LM358 dual op-amp IC – 1
- Piezoelectric disk – 1
- Resistors (2x 20kΩ, 2x 600kΩ, 1x 100kΩ, 1x 10kΩ)
- Potentiometer 100kΩ – 1
- Push button – 1
- CD4013B IC – 1
- Logic level MOSFET or transistor – 1
- Buzzer – 1
- Capacitor – 1x20mF
As you can see that output of comparator is connected to both flip flops of CD4013B. They set according to pulse of comparator which occurs when piezoelectric disk gets shock. “Q” output of first flip flop is connected to the gate of a MOSFET which drives the buzzer. “Q” output of second flip flop is connected to a RC circuit whose time constant is 2 seconds. Reset of first flip is pulled low to ground using 10kΩ resistor. It is connected to a push button and output of the RC circuit which pulls it high. Reset pin of first flip flop will get pulled high after 2 second or we can manually pull it high by pressing the button. Reset of second flip flop is connected to inverted “Q” output of first flip flop.
Working of smart security alarm circuit
First we get a voltage across the piezoelectric disk every time it get shocks then we amplified that voltage by a factor of 30. That amplified voltage then compared with a reference voltage. That will give a clean high or low digital pulse. Then that pulse sets both flip flops of CD4013B. This will turn the buzzer ON. After 2 seconds the RC circuit will reach the high threshold voltage and first flip flop will get reset and buzzer will stop screaming. Since first flip flop is now reset “inverted Q” output will be high. This will rest the second flip flop and RC circuit will start discharging. This cycle repeat every time this circuit feels any shock.