Darkness Detector as a Security Alarm - KhurafatiTech How to Tips-Tricks

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Tuesday, January 31, 2017

Darkness Detector as a Security Alarm




hello friends, this circuit can be used for both, as a dark detector or as a security alarm after making some modifications in it.
apparatus :

a light dependent resistor LDR, one LED and a carbon resistor 30k ohms, a battery 6V, n-p-n transistor,wires and soldering apparatuses.

procedure :


make the circuit according to the diagram just replace the resistor of 7.84k ohms by the light dependent resistor because it should vary with respect to the light. so that the current will flow through the led only when the resistance of the LDR is very high (some k ohms) it is obtained by the LDR in darkness. LDR gives very low resistance in the light so current flows through the LDR in light. in the darkness the current follow the low resistance path and it flows through the LED and transistor.

it can be used for security purpose also. if we connect an alarm to the LED and make an arrangement by the laser beam so that the beam falls on the LDR and the beam passes through the area where we need to stop the unknown people's entries. so when any person comes in front of the beam ,the LDR Detects darkness and the alarm will be activated and we can know the someone is entered in that area.

its working is showing in the video: watch the demo--




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