INDEX

LDR Specifications

resistance : 400ohm to 400Kohm
normal resistance variation: 1Kohm to 10Kohm (in the robots which i used for line following for identifying black and white strips)
sensitivity: about 3msec(Sensitivity is defined as the time taken for output to change when input changes, i got this reading by verifying with ADC interfaced with parallel port, sensitivity of LDR's is in milliseconds. This is the best sensitivity obtained to me).
Voltage ratings: I used it on 3V,5V and 12V
Practical application in Line follower Robots:
LED's are used with LDR which will act as a source of light for LDR because we are placing the LDR below the robot where light is not present. If we want to identify Black and White strips we add a light source with LDR and the white strip reflects light while black won't reflect light.

Above figure shows how LED is placed with LDR. Here LDR is covered because we want light reflections from ground only,not from sides of LED. Also cover the LED so that the light will move pointed, so that reflection will directly go to LDR. When you attach LED and LDR to the body of the
robot, use tape to paste the sensors. Remember if you robot body is of aluminum, then some short circuit or current flow can occurs through the body. So apply tape perfectly so that no short circuit problems occurs. Remember that LDR is a resistor and have no polarity while all other sensors have.

PROBLEMS: LDR is mainly used with visible light. So the problem of external light will affect the LDR. The affect of visible light is more in LDR then comes Photo diode, then TSOP1738.