![]() Now, to implement this we need a suitable value for R2. The voltage V out at the common terminal is given as: Lets call LDR as R1 and the fixed resistor as R2. By adding another fixed resistor in series we can form a potential divider network and can connect the common of the resister and LDR to ADC’s input pin. Once we do this it becomes very easy to interface them. ![]() Since we cannot directly connect an LDR to the ADC’s input, we need to convert the resistance into an equivalent voltage. You can check my LPC2148 ADC Programming Tutorial for reference. Under very bright light its resistance falls down to around few ohms, for example around 2 to 20 ohms.įor the examples covered in this tutorial, we will use the on-chip ADC module of LPC214x microcontroller to interface LDR. Under ambient light the resistance is generally around 2K to 10K. Hence under dark conditions the resistance typically rises to around 500K to 5M. The resistance of LDR is inversely proportional to the intensity of light. They are also known as photoresistors or photoconductive cells. LDR for short) is basically used to detect the intensity of light and hence, for example, we can detect if a room is dark or lit. This time we will go through a tutorial on Interfacing LDR with ARM7 LPC2148 microcontroller.
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