Keyhole Finder Circuit
This 3 volt Lithium cell operated LED flasher can be used as a key hole finder in darkness. A small lithium button cell can power the circuit more than 6 months continuously with day and night flashes. The circuit can also be used in key stand to search key in darkness.Use a high bright transparent 5 mm Yellow LED and fix the unit near the keyhole. The circuit is a simple oscillator comprising two complementary transistors BC 547 and BC557. These NPN and PNP transistors are wired as a simple oscillator with components C1 and R1 so that the LED flashes based on the charging and discharging of C1. Current consumption of LED is very low so that a normal 3 volt lithium battery can power the circuit for long time. A miniature 12 volt battery used in Car remote can power the circuit more than 2 years continuously.
EmoticonEmoticon