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Please note that these two schematics are independent.
Download datasheetRemote tester circuit also resembles the logic of a "dark sensor (using BC557)”. LDR has been replaced with IR sensor TSOP 1738. The circuit works as a remote tester. Pressing a remote control switch near the IR sensor, switches on the LED D2.

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Please note that these two schematics are independent.
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In this case, LDR has been replaced with capacitor C1-0.01uF and resistor R3-1K has been replaced with L1 & VC1. In...
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An automatic dark sensor can be made using a PNP transistor(BC557).
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