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With a significantly low cost you can make a bell with a modulated tone - "Bird" bell, whose sound is unusual and pleasing to the ear. Its circuit contains only one integrated circuit (UL 1111) and one transistor and is powered by one, or two flat batteries of 4.5 volts or a transformer (at the moment the transformer input is missing).
UL1111 - The integrated circuit includes all transistors except the pnp transistor (LOOK BELOW - I FOLLOW THE DIRECTION FROM LEFT TO RIGHT)!!!
1. The first transistor of UL1111, which is located after the PNP transistor, has the following terminals:
Base - 9;
Collector - 11;
Emitter - 10;
2.The second transistor of UL1111, which is located after the NPN transistor, has the following terminals:
Base - 6;
Collector - 8;
Emitter - 7;
3. The third transistor of UL1111, which is located after the second NPN transistor, has the following terminals:
Base - 4;
Collector - 5;
Emitter - 3;
5.The fourth transistor, which is located after the third NPN transistor, has the following terminals:
Base - 2;
Collector - 1;
Emitter - 3;
The device works as it follows. The pitch of the tone is generated by the multivibrator operating in autogeneration mode ( the FIRST transistor and the SECOND transistor from UL1111). The tone generated by this circuit is modulated by another multivibrator (the THIRD transistor and the FOURTH transistor from UL1111). Transistor T1 acts as a power amplifier for the speaker.
When powering the device through a transformer, the voltage must be rectified and filtered by a rectifier circuit. The circuit of the generator is supplied with stabilized voltage through the resistor 2K and the zener diode.
The frequency (pitch of the tone) can be adjusted with the potentiometer.
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