Sensitive Intruder AlarmCircuit using 555 IC and 741 IC
#555 IC
#741 IC
#intruder alarm
#LDR
#comparator
#sensitive alarm
#security system
#shadow detection
Description: The circuit diagram represents an ultra-sensitive intruder alarm. A shadow from an intruder passing nearby is sufficient to trigger the alarm. The operational amplifier IC2 (uA 741) is configured as a sensitive comparator, with its set point determined by resistors R6 and R7. The voltage divider formed by the Light Dependent Resistor (LDR) and resistor R9 is connected to the non-inverting pin of IC2. In standby mode, these two voltages are equalized by adjusting R9, resulting in a high output (pin 6) from the comparator, which keeps transistor Q1 in the off state. Consequently, the trigger pin of IC1 receives a positive voltage, and the alarm remains inactive. When an intruder approaches the LDR, the shadow causes an increase in its resistance. This change results in different voltages at the inputs of the comparator, leading to a low output from IC2, which turns on Q1. This action generates a negative-going pulse to trigger IC1, configured as a monostable multivibrator. The output from IC1 is then amplified by transistor Q2 (SL 100) to sound the alarm. Proper sensitivity adjustment is crucial; if the desired sensitivity cannot be achieved, a low-resistance potentiometer (approximately 1K ohm) can be added in series with R9 for fine-tuning.
The ultra-sensitive intruder alarm circuit employs a combination of analog components to detect minute changes in ambient light levels caused by the presence of an intruder. The circuit's core component, the uA 741 operational amplifier, functions as a comparator, comparing the voltage levels from the LDR and the reference voltage set by resistors R6 and R7. The LDR's resistance decreases in bright light and increases in darkness, allowing it to detect shadows effectively.
In the circuit's normal operation, the voltage divider formed by the LDR and R9 maintains a balance between the two input voltages of the comparator. Adjustments to R9 allow for calibration of the circuit's sensitivity to ambient light changes. When an intruder casts a shadow on the LDR, the change in resistance alters the voltage at the non-inverting input, causing the comparator's output to switch states.
Transistor Q1 acts as a switch that controls the triggering of the monostable multivibrator (IC1). When the output of the comparator goes low due to the shadow detected by the LDR, Q1 turns on, sending a negative pulse to IC1. This pulse causes IC1 to generate a single output pulse that remains high for a predetermined duration, determined by the external timing components connected to it.
The output pulse from IC1 is then amplified by transistor Q2 (SL 100), which drives the alarm system. This amplification ensures that the alarm can produce a loud sound or signal sufficient to alert individuals in the vicinity of the intrusion.
For optimal performance, it is essential to fine-tune the sensitivity of the circuit. The addition of a low-resistance potentiometer in series with R9 allows for precise adjustments, ensuring that the alarm is triggered only under the desired conditions, thereby minimizing false alarms and enhancing reliability.Here is the 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 volt ages 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. 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.
The ultra-sensitive intruder alarm circuit employs a combination of analog components to detect minute changes in ambient light levels caused by the presence of an intruder. The circuit's core component, the uA 741 operational amplifier, functions as a comparator, comparing the voltage levels from the LDR and the reference voltage set by resistors R6 and R7. The LDR's resistance decreases in bright light and increases in darkness, allowing it to detect shadows effectively.
In the circuit's normal operation, the voltage divider formed by the LDR and R9 maintains a balance between the two input voltages of the comparator. Adjustments to R9 allow for calibration of the circuit's sensitivity to ambient light changes. When an intruder casts a shadow on the LDR, the change in resistance alters the voltage at the non-inverting input, causing the comparator's output to switch states.
Transistor Q1 acts as a switch that controls the triggering of the monostable multivibrator (IC1). When the output of the comparator goes low due to the shadow detected by the LDR, Q1 turns on, sending a negative pulse to IC1. This pulse causes IC1 to generate a single output pulse that remains high for a predetermined duration, determined by the external timing components connected to it.
The output pulse from IC1 is then amplified by transistor Q2 (SL 100), which drives the alarm system. This amplification ensures that the alarm can produce a loud sound or signal sufficient to alert individuals in the vicinity of the intrusion.
For optimal performance, it is essential to fine-tune the sensitivity of the circuit. The addition of a low-resistance potentiometer in series with R9 allows for precise adjustments, ensuring that the alarm is triggered only under the desired conditions, thereby minimizing false alarms and enhancing reliability.Here is the 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 volt ages 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. 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.
Simple Analogue Electronic Key
This circuit utilizes two comparators configured as a window comparator. Resistors R2, R5, and R10 establish a voltage window within which the voltage at the junction of D2 and D6 must reside for the outputs of IC2.A and IC2.B to...
lights led circuits schematics
The circuit employs two Light Dependent Resistors (LDRs) arranged in series with a separation of approximately half a meter. This configuration allows each LDR to detect the presence of a person entering or exiting the room. The processed outputs from...
Automatic cycle switch circuit 2
An automatic cycle switch circuit utilizing a 555 integrated circuit (IC) as the control element. It incorporates a capacitive step-down circuit and employs a bidirectional thyristor to control relays or loads with specific on and off timing. The circuit includes...
Comparator for over-voltages
To maintain an alarm condition when an overvoltage transient disappears, an SCR should be added to the comparator circuits. For SCR operation, the voltages to the comparator inputs are inverted. The triple-voltage monitoring circuit detects transient power-supply over-voltages. If excessive...
File Alarm with LDR Sensor
This circuit is an alarm system that utilizes an LDR (Light Dependent Resistor) sensor. The sensitivity of the circuit is influenced by the distance between the light bulb and the LDR, as well as the setting of the preset variable...
%2Busing%2Bop%2Bamp%2B741%2Bic%2B.png "Zero Crossing Detector ZCD Comparator circuit using 741 op amp circuit")
Zero Crossing Detector (ZCD): Comparator circuit using 741 op amp
A zero crossing detector (ZCD) is a voltage comparator that switches its output between +Vsat and -Vsat (where Vsat is the saturation voltage, approximately 14V) when the input crosses the zero reference voltage. Comparators are fundamental operational amplifier circuits that...
Simple Fire alarm circuit using LDR
This document describes a simple fire alarm circuit utilizing a Light Dependent Resistor (LDR) and lamp combination for fire detection. The alarm activates by detecting smoke generated during a fire. When smoke is present, the circuit triggers an audible alarm....
Comparator-latch
The main advantage of this circuit, in comparison to other comparators, is its capability to latch once the input surpasses a specified threshold level. When the input goes beyond this threshold, the output of the LM311N rises. This change activates...
Alarm and Security Circuits
This section includes intruder alarms for homes, cars, and motorcycles, as well as power failure alarms, water level alarms, and a snore detector. All circuits are organized alphabetically on the Circuit Index page and chronologically on the update page. Contributors...