This project produces a sound of a parrot [Like]. This can be used as a calling bell, fitted in toys, remote bell etc.
TECHNICAL DESCRIPTION & WORKING:-
This project has been developed and successfully tested in TV Engineer Technical Lab.
Now a days different types of calling bells are used in homes, many of which produce unpleasant and harse sounds. Also these sounds have adverse effect on human being and children are afraid of it. The project given below produces a very pleasant sound, similar to the sound of a parrot. This can replace the conventional calling bells fitted in homes. This is why this bell is called PARROT BELL.
In this circuit transistor TR-1 BEL 187, an NPN transistor is used as a audio frequency amplifier.
This Circuit works on 220 V AC. It is based on Hartley Oscillator. As can be seen from the diagram given below, the centre tape of output transformer is supplied voltage through a diode – IN 4001 and one end of winding is connected to collector to collector of TR-1. The emitter of the transistor is directly earthed. The base of the transistor is biased through R-2 56K 1/4W. To produce the desired frequency a feed back net work completed by connecting R-3 [1KE] and C-3 [.1MFD] to the base of transistor. Here the RC time constant circuit is complete through R-4 1K 1/2W and C-2 33MFD/12V which are connected to the base and emitter.
The transistor TR1 [BEL 187] works on 10V DC which is available through the output transformer. Base biasing is given through R-2 56K 1/2W. The audio frequency produced through the oscilation of the transistor is available through the secondary winding of the output transformer is connected to a 8E speaker. The speaker converts the audio frequency into sounds, which is similar to the sounds produced by a parrot.
The 10 Volt DC is produced by using a dropping resistance R-1 1K5 [10W] and a rectifier diode. Capacitor C1 1000MFD/12V works a filter as well as a charger. When we push the switch of the bell, the sound comes for sometime, which is due to this capacitor. The sound stops as soon as the capacitor get discharged.
PRECAUTIONS WHILE ASSEMBLING THE PROJECT
- First check all components as per the circuit.
- Check transistor TR-1 BEL 187.
- Pay proper attention to the polarity of capacitors and diodes while assembling.
- While mounting transistor, be sure that you have connected collector, emitter and base properly.
- Clean PCB after soldering so that components do not short.
LIST OF COMPONENTS:-
R1-1.5K 10WATT [1NOS]
R2-56K 1/4W [2NOS]
C2-33 MFD/12V [1 PC]
C3-.1MFD/50V [1 PC]
C4-.04/50V [1 PC]
- SEMI CONDUCTORS
DIODE IN 4007 [1 NOS]
TRANSISTOR BEL 187 [1 NOS]
OUT PUT TRANSFORMER [1 NOS]
SPEAKER 8 OHMS [1 NOS]
CHOKE TRANSFORMER [1 NOS]
FLEXIBLE WIRE, SOLDER, PASTE ETC.