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L25, Simple Door Bell Timer, With Adjustable Timing Facility

This simple transistor circuit can be used as a home door bell and it’s ON time can be set as preferred by the user, meaning if you wanted that the sound of the bell to remain switched ON for a particular period of time, you could easily do it just by adjusting the given pot.

The actual tune is derived from the IC UM66 and the associated components, while all the included transistors along with the relay are configured for producing the time delay for keeping the music switched ON.


  • R1, R2, R4, R5 = 1K

  • VR1 = 100K,

  • D1, D2 = 1N4007,

  • C1, C2 = 100uF/25

  • T1 = BC547,

  • T2 = BC557

  • T3 = 2N2222

  • RL = 1 henry

  • Z1 = 3V/400mW

  • Transformer = 0-12V/500mA,

  • S1 = Bell Push

  • Buzzer

  • IC = UM66

  • Transformer AC-DC 9volt

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