The project about light sensor circuit shows the application of photodiode to detect the presence of light. This light sensor can be used as an intermediate circuit [[wysiwyg_imageupload::]]in various applications to detect the presence or absence of light. The sensitivity of the sensor can be adjusted using the preset. This circuit is based around a LM339 comparator along with variable capacitors, photodiode, LED and a solo resistor. A photodiode, used as a photo detector, generates current in the circuit when light incidents on it. The circuit of this project uses the photodiode in reverse bias mode with resistor R1. The LED at the output will glow when light falls on the diode. In such a condition, the inverting input drops to a lower value than the reference set at the non-inverting input and so the output goes providing the necessary forwards bias to the LED.
The circuit described here can be used as burglar alarm or can be used as an indicator that door or window is open.Now the summer time is coming and we all are going to use AC in our home and offices. AC functions efficiently, only when doors and windows are closed properly. If any of the door or window is left open then effect of AC cannot be felt. So we have described a circuit here that will give an alarm when door or window is left open.Another application when you can use this circuit, in your cupboard or lockers. When light fall on the sensor it will give an alarm indicating that somebody is trying to steal your valuable thing. And will also give an alarm when any unwanted person is trying to open door and window.