July 13, 2009

Secret Bell

9:20 PM  Sabarish  No comments

Secret Bell
Many people move through the corridors and steps in multi storied buildings. As most of them are strangers for the inhabitants of the flats, it becomes necessary to verify the identity of the visitor before opening the door as he can be a burglar. This circuit helps you identify the members of your family. It is basically a switch less musical bell that activates with a single puff of breath. The condenser mic fitted inside the existing door-bell switch box will trigger the bell on detecting air-pressure changes following the breath. As only the members of your family know the secret of the bell and hence puff out before the hole for the switch box, the door can
be opened without fear.

Working
The front end of the circuit is a condenser mic amplifier with fixed sensitivity. Transistor T1 amplifies the signal received from the condenser mic through capacitor C1. When transistor T1 conducts, a short negative pulse triggers the monostable wired around IC1. The monostable time is decided by resistor R7 and capacitor C5. Reset pin 4 of IC1 is made stable by R6 and C3. Resistor R5 acts as a pull-up resistor for trigger pin 2 of IC1 to keep the trigger pin high in the standby mode. The high output from IC1 is used to power IC UM66 (IC2). IC2 generates a soft melody on receiving 3 volts at pin 2. Transistor T2 amplifies the music
notes. A zener diode maintains the power for IC2 at a safer level of 3 volts. The condenser mic
should be connected to the circuit using a single-core shielded wire to reduce noise interference

Circuit Diagram


Note : Click the image for better Quality

Posted in:

0 comments:

Post a Comment

DOOR BELL FOR DEAF CLICK HERE

Electronics is the study and use of electrical that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves. and semiconductors. The pure study of such devices is considered as a branch of physics, while the design and construction electronic circuits to solve practical problems is called electronic engineering.

Popular article

  • 50 Watts Inverter Circuit
    A 50 watt inverter might look quite trivial, but it can serve some useful purposes to you. When outdoors, this small power house can be ...
  • A-Z Circuit Symbols
    The following table covers almost every circuit symbol you will need. This is the English/American version of each symbol. The Europea...
  • Superposition Theorem
    S uperposition Theorem Superposition theorem is one of those strokes of genius that takes a complex subject and simplifies it in a way that ...
  • Transformer
    In real this is how an TRANSFORMER looks like.. the transformer is a device that transfers electrical energy from one end of the coil to th...