Simple Shadow Detector Security Alarm Circuit

This Shadow Detector Security Circuit is like a guardian with super sight.

It uses a light sensitive piece like a photodiode to watch for shadows moving in a specific area.

If something blocks the light and creates a shadow the circuit knows someone might be there and triggers an alarm.

This can be a loud buzzer, a flashing light or any other way to get your attention.

These circuits are a popular choice for security systems because they can detect movement without needing fancy cameras or expensive sensors.

So, next time you want to keep an eye on things this circuit can turn shadows into silent alarms!

Circuit Working:

Parts List:

This shadow alarm circuit detects movement in a confined area using a light sensitive PIN photodiode.

It can be utilized to safeguard against theft by emitting a loud alarm when someone approaches.

The circuit employs the light-sensing property of the photodiodes p-n junction, which produces a light current when forward biased.

IC1 serves as a voltage comparator, with its non inverting input connected to a potential divider R1 and VR.

By adjusting VR, the input current to pin 3 can be set to a reference level.

The inverting input of IC1 is linked to the photodiode.

The CA 3130 IC is a 15 MHz BiMOS operational amplifier with MOSFET inputs and bipolar output.

It features MOSFET transistors in the inputs for high input impedance and low input current as low as 10pA, enabling high speed performance suitable for low input current applications.

The CA 3130A and CA 3130 op amps combine the benefits of CMOS and bipolar transistors.

Gate protected P Channel MOSFET PMOS transistors in the input circuit offer very high input impedance, very low input current, and exceptional speed performance.

These transistors also allow common mode input voltage capability down to 0.5V below the negative supply terminal crucial for single supply applications.

The output circuit utilizes a CMOS transistor pair capable of swinging the output voltage to within 10mV of either supply voltage terminal, particularly at high values of load impedance.

The CA 3130 Series operates at supply voltages ranging from 5V to 16V, can be phase compensated with a single external capacitor and have terminals for offset voltage adjustment for applications requiring offset null capability.

The CA 3130A offers superior input characteristics compared to the CA 3130.

Under normal light conditions as set by VR, the photodiode provides voltage to pin 2 of IC1.

Since this voltage exceeds the voltage set by VR at pin 3 the output of IC1 remains low, keeping the LED and buzzer off.

However, when someone approaches the photodiode casting a shadow and reducing the current through it, the voltage at pin 2 decreases below that of pin 3.

This change causes the output of IC1 to go high activating the buzzer.

Formula:

An operational amplifier CA 3130 and a photodiode are used in this shadow detector security alarm circuit to sense variations in light levels.

The precise equations employed in the circuit design, however will rely on the intended functionality of the alarm.

The general formula listed below could be applicable to the circuit type mentioned above:

Resistor potential divider formula:

This formula is commonly used to determine the reference voltage for the operational amplifier by calculating the voltage at a given point in a voltage divider circuit:

V_out = V_in * (R2 / (R1 + R2))

where,

• Vout is the voltage at the voltage dividers output.
• Vin is the voltage that is applied to the voltage dividers input.
• R1 and R2 are the resistances of the two resistors in the voltage divider

Formula for an operational amplifier comparator:

In this circuit, the operational amplifier is probably being utilized as a comparator.

When two voltages are compared, a comparator determines which of the two is higher and generates a high or low signal.

The exact formula is used to calculate the comparators output will vary depending on the operational amplifier design, but it will often be based on the difference between the two input voltages.

How to Build:

To build a Simple Shadow Detector Security Alarm Circuit follow the below steps:

Power Connections:

• Connect the positive terminal of the power supply to pin 8 VCC of the CA 3130 IC and the negative terminal to pin 4 ground.

Voltage Reference Setup:

• Connect pin 3 non inverting input of the CA 3130 IC to a potential divider consisting of R1 100k resistor and VR 10k preset.
• Adjust VR to set the reference voltage.

Photodiode Connection:

• Connect the anode of the photodiode to pin 2 inverting input of the CA 3130 IC and the cathode to the ground.

Output Connection:

• Connect pin 6 output of the CA 3130 IC to the anode of the LED through a current limiting R2 resistor 100Ω.
• Connect the negative terminal of the buzzer to the ground.

Testing:

• Apply power to the circuit.
• In normal light conditions, the LED should remain off indicating that the photodiode is receiving sufficient light.
• When a shadow is cast on the photodiode the LED should turn on and the buzzer should sound, indicating that the circuit has detected the shadow.

Adjustment:

• If necessary, adjust the sensitivity of the circuit by tweaking the VR preset to set the trigger point for the alarm.

Note:

• The circuit is triggered by changes in light intensity without a shadow.
• It’s advisable to place the unit where constant light is available.

Conclusion:

To conclude, a shadow detector security alarm circuit is a valuable component in security systems using light sensitive technology to detect shadows and trigger an alarm alerting users to potential intrusions or unauthorized movement.

References:

Datasheet IC CA3130