single IC siren

single IC siren a physical sense. This particular siren is very simple and easy to cin- struct since it is built around a single IC, the LM 389 from National Semiconductors. This IC contains an audio power amplifier, similar to the LM 386, Circuits that produce some sort of noise appear to be highly popular with many readers. A possible eratio reason for this is that correct circuit operation is verified audibly and without the need for test equip- ment, in other words, the circuit does something in together with three uncommitted NPN tran- sistors. d T2 form the basis of an 1025V0 mpo The two transistors Ti an astable multivibrator with a frequency variable between 1 and 7 Hz. The preset P1 is used to adjust ed as a square this. The amplifier is also configurrives the l wave oscillator and its output d speaker at frequencies variable between 250 Hz and 1500 Hz. The amplifier, however, is switched one and off by the multivibrator via transistor T3. The The frequenc result is a p...