How to Test LDR(Find bad LDR)

LDR: A photoresistor (or light-dependent resistor, LDR, or photo-conductive cell) is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light-activated and dark-activated switching circuits.

Method #1:

Required parts: digital multimeter, LDR

Step1: first turn ON the digital multimeter and select the digital multimeter knob to resistance mode.

Step2: then, connect the all connection like this below image.

Step3: Now, you will see the digital multimeter display. it's shows the resistance value. the resistance value will change from different light intensity. 

Step4: If the resistance value will change from different intensity the LDR is good condition or resistance value is not change the LDR is damage.

Method #2:

Required parts: digital multimeter, LDR, 10K Resistor, 5V DC power supply

• First connect the all connection like this above image. This circuit is resistor pull-up method. now, you will give the power supply. when light source is increase the voltage will decrease and light source is decrease the voltage will increase. if the condition is possible the LDR is good condition or the LDR is damage.

Method #3:

Required parts: digital multimeter, LDR, 10K Resistor, 5V DC power supply

• First connect the all connection like this above image. This circuit is resistor pull-down method. now, you will give the power supply. when light source is increase the voltage will increase and light source is decrease the voltage will decrease. if the condition is possible the LDR is good condition or the LDR is damage.

Method #4:
Required parts: LDR, 10K Resistor(3), 5V DC power supply, 100 Ohm's resistor(2), Green LED, Red LED, PNP Transistor, NPN Transistor

• First connect the all connection like this above image. now, you will give the power supply. when light source is increase the Green LED will ON and light source is decrease the Red LED will ON. if the condition is possible the LDR is good condition or the LDR is damage.

Method #5:
Required parts:LDR, 10K Resistor(3), 5V DC power supply, 100 Ohm's resistor(2), Green LED, Red LED, PNP Transistor, NPN Transistor

• First connect the all connection like this above image. now, you will give the power supply. when light source is increase the Red LED will ON and light source is decrease the Green LED will ON. if the condition is possible the LDR is good condition or the LDR is damage.