Auto switching USB LED desktop lamp is a very simple in design but has very important role in our daily life. This project is based on Light Dependent Resistor (LDR) and a high current NPN transistor (BD139).this lamp will be powered from any USB port (like laptop, desktop, mobile charger, etc.) and lamp will be switch ON when there is no light and switch OFF when there is any light. LDR is used to sense light intensity of the environment and gives corresponding response in change in resistance of the LDR. The change in resistance of LED is changes into potential drop across it. This potential drop is then used to switching the transistor ON or OFF. This transistor is connected as a switch to the LEDs through a current limiting resistor.
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