Schematics Two-Door Doorbell Circuit PCB | Electronic Circuits

Schematics Two-Door Doorbell Circuit PCB

The circuit described her is different form conventional door bell circuits in the sense that it can produce two different tones-one of a lower frequency and the other of a much higher frequency. The circuit uses a timer IC 555, which has been wired in free-running mode. When switch S1 is depressed, the circuit oscillates at around 1.5 kHz, resulting in a higher frequency note. When switch S2 is depressed, transistor T1 is turned 'on' and thus it shunts resistor R2 across capacitor C2. As a result, the circuit now oscillates at approximately 150 Hz and a tone of much lower frequency is generated.

Circuit diagram of Two-Door Doorbell  : Click on image to enlarge

The circuit can be conveniently employed as a doorbell for two separate doors at the same floor level. Doorbell switches S1 and S2 can be mounted near the re-spective doors. The circuit can be assembled on a
general-purpose PCB and housed inside a small cabinet. Tone can be adjusted with the help of preset VR1. Before power is switched 'on' , it is advisable to adjust VR1 to approximately 5 kiloohm, that is, at the centre of the full range of potentiometer VR1. A trimpot can be used as VR1 for convenience of assembly.

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