Various types of security-based projects are already available on bestengineeringprojects.com. Now here is sound operated light and alarm that is used as an intruder alarm, activated when any sound is detected (like the opening of doors, knocking, or door opening) and starts flashing with a sound that alerts you of an intruder. After the second sound pulse is turned off.
Circuit Description of Sound Operated Light and Alarm
The circuit of sound-operated light and alarm is designed using a pair of timer IC (NE555), a dual JK flip flop IC (CD 4027), and an op-amp IC (CA3140).
The input from the AC mains is given to the primary side of transformer X1 for stepping down. The stepped-down voltage is further rectified (Half Wave Rectifier) and filtered by diode D1 and capacitor C1 respectively. The reference voltage is given to the non-inverting input (pin 3) of op-amp IC (IC1) and is set by variable resistor VR1.
A microphone (MIC1) is used as a sensor that detects sound and converts it into an electrical signal which is given to inverting input (pin 2). The voltage that appeared at pin 2 is equal to the voltage across the condenser microphone, which is set for the high sensitivity of the sound. The reference voltage is kept high which means a small sound is enough to change the output of IC1. To keep output voltage unchanged for any false triggering the reference voltage is kept fixed.
At initial when no sound is detected by the microphone, the voltage that appeared in its inverting input is equal to the DC voltage from the power supply and hence no output appears at the output of IC1 (pin 6). Since IC2 (CD4027) is a dual JK flip-flop and is wired in toggle mode thus no output is obtained at the output of IC2 (pin 15). The low output at pin 15 of IC2 makes reset pin 4 of IC3 low to reset the IC3 (NE555) which is wired in astable multivibrator mode. As a result, the output of IC3 becomes low which drives transistor T1 in cut-off and keeps relay RL1 remaining de-energized. Both N/O (N/O1 and N/02) contacts remain open. The N/O2 contracts keep bulb B1 turned off, where N/O2 contact keeps the loudspeaker circuit open and hence no sound has appeared on the loudspeaker.
When any sound is detected by the microphone it reduces the inverting voltage because some voltage is dropped by the microphone its elf. Hence the output of IC1 is high, which triggers IC2 and makes output high (IC2). As the output of IC2 is connected to the reset pin of IC3 which enables an astable multivibrator for 1.5 seconds. This process repeats until pin 15 of IC2 remains high. The high output of IC3 drive transistor T1 conduction region and further relay is also energized. The energized relay light up the bulb B1 and at the same time audio tone is generated.
When another sound is detected by the microphone, the output of IC2 goes low and resets the astable multivibrator (IC3) which again puts the transistor in the cut-off region and further relay is de-energized.
Check out other security-based projects posted on bestengineeringprojects.com
- RFID Based Security System Using Microcontroller AT89C52
- Luggage Security System
- Automatic Fence Lighting with Alarm
- Arduino and RFID based Door Access System
PARTS LIST OF SOUND OPERATED LIGHT AND ALARM CIRCUIT
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 = 33 KΩ
R2, R9 = 1 KΩ R3 = 470 Ω R4, R7, R8 = 10 KΩ R5, R6 = 470 KΩ VR1 = 1 KΩ |
| Capacitors |
| C1 = 1000 µF, 25V (Electrolytic Capacitor)
C2 = 4.7 µF, 35V (Electrolytic Capacitor) C3, C5 = 0.01 µF (Ceramic Disc) C4, C8 – C11 = 0.1 µF (Ceramic Disc) C6 = 100 µF, 25V (Electrolytic Capacitor) C7 = 10 µF, 25V (Electrolytic Capacitor) |
| Semiconductors |
| IC1 = CA3140 (BiMOS Operational Amplifier)
IC2 = CD4027 (Dual JK Master Slave Flip-Flop) IC3, IC4 = NE555 (Timer IC) D1, D2 = 1N4001 (Rectifier Diode) T1 = BC548 (general-purpose NPN bipolar junction transistor) |
| Miscellaneous |
| RL1 = 12V, 200Ω, 2C/O Relay
LS1 = 8Ω/0.5W speaker MIC1 = Condenser Microphone X1 = 230V AC primary to 12V, 250 mA secondary transformer B1 = 60W, 230V Bulb |