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Light intensity meter

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New Member
I am making a light intensity meter in percentage of 10% - 100% (To be shown on 7 segment display: 10,20,30...100) . The display will be in 7segment and using a 8051 microcontroller. Attached is the light intensity circuit that varies in voltage depending on light intensity.
I need help in merging this light intensity circuit to display on the 7segment using 8051 microcontrollers.

light detector.gif

*Currently unsure on how to input signals to the microcontroller for 10 different range of voltage (10% 20% 30%...100%) to display on the 7 segment*

Any advice or suggestion would be appreciated =) thanks!!
Last edited:


Well-Known Member
Most Helpful Member
Your extremely simple circuit turns on the relay when it gets dark.
The output voltage of the transitor changes when the amount of light changes and it also changes when the temperature changes.

You should use an opamp instead of the transistor to give an accurate voltage. Then a transistor can be driven from the opamp and drive the relay.
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