Circuit of a 555 Multi-vibrator with a changeable tone

Published:2011/9/3 10:38:00 Author:Zoey | Keyword: 555 Multi-vibrator, a changeable tone | From:SeekIC

This transposition circuit is composed of two time-based 555 circuit, it can emit continuous oscillation wave that ranges from 400~2500 Hz, similar to the sound of police wagon. This circuit consists of time-lapse oscillator, low-frequency oscillator and modem audio generator; the circuit can be seen in the picture3-21. The gating switch HG is magnet-controlled and it remains open usually. When IC1 ceases to be reposited and starts to oscillate, the oscillation frequency is fc=1.44/(R2+2R3)C2 The charge and discharge time of C2 is 3.94s and 0.06s respectively. Output wave of C2 is sawtooth voltage wave, which controls the oscillation frequency conversely. The multi-vibrator is composed of IC2,R4, R5 and C3, with its frequency can be changed. Its basic oscillation frequency is about 1000Hz, and its actual oscillation frequency changes as sawtooth voltage wave change. The oscillation square wave will be magnified through VT2, and then drive the speaker to make an alarm that sounds like the police wagon. The circuit can be used in burglarproof system and circuit of various toys, the prolonged time of start-up can be adjusted according to the time takes for housemasters to enter the house. For example, it takes longer time for old people to enter the house, so we can prolong the time by enlarging the time constant of R1C1.



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