Light detector circuit (CLAP4 assignment) RA2111027010181

Light detectors are designed to convert low light levels into an electric signal of reasonable amplitude to avoid deterioration of the signal by external noise or pick-up. Here, in the circuit we are using resistors , one 5 terminal opamp , an LED , a DC voltage source finally connecting grounding. We can change the resistance of the variable resistor for the LED to light up. An LDR, as the name suggests, is a type of resistor, whose resistance changes depending on the intensity of the light surrounding it. Typically, when light is incident directly on the LDR, its resistance will be very low and when there is no light i.e. in darker conditions, its resistance jumps to few mega Ohms. We will use this feature of the LDR is our project to detect light and turn on an LED. For this we have used an Operational Amplifier. The Op – Amp is configured in Comparator mode i.e. it will compare the voltages at inverting and non – inverting terminals and correspondingly generate a HIGH or LOW output. We have connected the wiper terminal of the 10 KΩ Potentiometer to the inverting terminal of the OP – Amp. To the non – inverting terminal, we have connected the junction of a 10 KΩ Resistor and the LDR. These two will form a potential divider feeding its output to the OP – Amp. When the light is incident on the LDR, its resistance decreases. Hence, the non – inverting voltage is lower than the inverting voltage and as a result, the LED remains OFF. When there is no light falling on the LDR, the resistance of the LDR becomes very high and as a result, the voltage at the non – inverting terminal will be more than the voltage at inverting terminal. The output of the Op – Amp will be high and the LED is turned ON.