Two door Door Bell

The Two-door Dorbell is capable of generating two different tones: one of a lower frequency and the other of a much higher frequency. The circuit can be simply mounted on two different doors on the same floor and separate switches can be provided to generate the two distinct tones. No. of ICs used: 2 The heart of the Two-door Doorbell is the NE555 timer IC which operates in the free-running mode. When switch S1 is depressed, the circuit oscillates at around 1.5 KHz, resulting in a high frequency note. On the other hand, when switch S2 is depressed, the NPN transistor SL100 (denoted as T1) is turned ON and this shunts a resistor across capacitor (C2). As a result, the circuit now oscillates at approximately 150 Hz and a tone of much lower frequency is generated. Learning: Application of the NE555 timer IC to generate tunes of two different frequencies. Application of voltage regulators such as the 7806. Application of NPN transistor as switches Brand: Kits'n'spares, Marketed by: Kits'n'spares