Showing posts with label intruder. Show all posts
Showing posts with label intruder. Show all posts
Saturday, November 15, 2014
SENSITIVE INTRUDER ALARM CIRCUIT
This circuit diagram of an ultra sensitive intruder alarm. The shadow of an intruder passing few meters nearby the circuit is enough to trigger the alarm. Here IC2 uA 741 is wired as a sensitive comparator ,whose set point is set by R6 &R7. The voltage divide by LDR and R9 is given at non inverting pin of IC2. At standby mode these two voltages are set equal by adjusting R9. Now the output (pin6) of comparator will be high.Transistor Q1 will be off. The voltage at trigger pin of IC1 will be positive and there will be no alarm. When there is an intruder near the LDR the shadow causes its resistance to increase. Now the voltages at the inputs of comparator will be different and the out put of IC2 will be low. This makes Q1 on. This makes a negative going pulse to trigger the IC1 which is wired as a monostable multivibrator.The out put of IC1 will be amplified by Q2 (SL 100) to produce alarm.
Intruder Alarm Circuit Diagram with Parts List
Notes
- To setup the alarm ,power up the circuit and adjust R9 so that LED D1 goes off.
- The LDR can be housed in a dark tube to increase sensitivity.
- The sensitivity is very important here. If you cannot adjust the required sensitivity properly, use one LOW resistance (~1K ) POT in series with R9 for fine adjustment.
Monday, August 11, 2014
Intruder Detector Using Laser Torch
Here is a simple, low-cost intruder detector that uses an invisible laser beam to detect the intruder. The laser beam is produced using a 3V DC or 4.5V DC laser pointer or torch that is available in the market. The 3V DC or 4.5V DC power supply for the laser transmitter can also be given using a bridger ectifier or full-wave rectifier.
Fig. 1 shows the block diagram of the complete unit comprising the transmitter and receiver sections. The laser beam from the transmitter after reflection from various mirrors (M1 through M6, as shown in Fig. 1) is made to fall on the photodetector in the receiver schema.
Once the laser beam is positioned, the receiver schema is powered by closing switch S. An alarm unit operating on 230V AC is connected to the relay RL in the receiver schema.
When an intruder interrupts the path of the beam or switches off the laser torch, the alarm unit becomes activated. The alarm unit remains activated until reset switch S is opened. To activate the alarm schema again, reset switch S should be closed. The total distance travelled by the laser beam should be less than 800 m for 4.5V laser torch and 500 m for 3V laser torch.
The schema of the receiver is shown in Fig. 2. When reset switch S is closed, the schema is powered on. As the laser beam falls on the photodetector, transistor T (BC547) conducts, resulting in the collector being pulled down to ground potential. Thus no current flows to the gate of the SCR and it remains off.
Once the path of the laser beam is interrupted, the base current of the transistor becomes very low and the transistor is driven to cut-off. Now the current starts to flow through resistor R1 and to the gate of SCR. Hence the SCR is fired and it begins to conduct. Thus relay RL connected to the anode of SCR is switched on and the alarm is activated. The alarm sounds until reset switch S is opened to turn off power to the schema.
EFY Lab note. We tested the schema using only one mirror and found its range to be 25-30 metres. The range depends on the intensity of laser beam falling on the photodetector.
The schema (excluding laser torch and mirrors) costs around Rs 100.
Fig. 1 shows the block diagram of the complete unit comprising the transmitter and receiver sections. The laser beam from the transmitter after reflection from various mirrors (M1 through M6, as shown in Fig. 1) is made to fall on the photodetector in the receiver schema.
Fig. 1: Block diagram of intruder detector using laser torch
Once the laser beam is positioned, the receiver schema is powered by closing switch S. An alarm unit operating on 230V AC is connected to the relay RL in the receiver schema.
When an intruder interrupts the path of the beam or switches off the laser torch, the alarm unit becomes activated. The alarm unit remains activated until reset switch S is opened. To activate the alarm schema again, reset switch S should be closed. The total distance travelled by the laser beam should be less than 800 m for 4.5V laser torch and 500 m for 3V laser torch.
The schema of the receiver is shown in Fig. 2. When reset switch S is closed, the schema is powered on. As the laser beam falls on the photodetector, transistor T (BC547) conducts, resulting in the collector being pulled down to ground potential. Thus no current flows to the gate of the SCR and it remains off.
Fig. 2: Receiver schema
EFY Lab note. We tested the schema using only one mirror and found its range to be 25-30 metres. The range depends on the intensity of laser beam falling on the photodetector.
The schema (excluding laser torch and mirrors) costs around Rs 100.
Sourced by : EFY Author : G. Susinder Rajan
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