AM Bhatt over at Engineers Garage writes:
In the given project, LDR is used to measure light intensity inside the room. With a minor change in the circuit, it can be used to measure outdoor light intensity also. It uses microcontroller AT89C52 and LCD to display light intensity. It also indicates how much light inside room like “full light”, “good light”, dim light” etc. However, microcontroller cannot detect the change in resistance directly. LDR has to be given biasing voltage along with pull up or pull down resistance so that change in resistance is converted into change in voltage. The change in analog voltage is converted into digital equivalent using ADC and this digital value is read by microcontroller. Let us discuss this in somewhat more detail manner.
More details at Engineers Garage homepage.
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