Robotics Tutorials - Intermediate - Hardware - Light Sensors

The beginners section hopefully made you think a little about some of the uses of light dependant resistors or LDR's. To use them you need to make a circuit called a potential divider, or a circuit that splits voltage (or potential). It looks something like this: This circuit is necessary because the any circuit that uses the ATD must be connected to ground for accurate readings to be possible. The circuit can be explained with a bit of maths. The voltage out of a potential divider is Voltage Out = V in X LDR resistance Resistor + LDR resistance If we think about this equation a bit we can see that Vin is always 5 volts, and the resistance of the fixed resistor is always 10,000 ohms (or 10 kilo ohms). We know that the resistance of the LDR is dependant on the brightness of the light shining on it. In the dark it has a very high resistance, where as in bright light it has a very low resistance. So therefore, the output voltage of the potential divider will vary linearly according to the level of light on the LDR. This circuit can be easily made on a small piece of strip board or a breadboard.