Selective Door Chime Circuit Diagram

Introduction

The chime is for use in situations where there is bell or chime at the front door as well as at the back door. When loud bells or chimes are used, it may be difficult to determine which one is being rung. This Selective Door Chime Circuit will solve this problem which can produce two or three different sounds. When two of these circuits are built, the one at the front door is set to produce, say, two tones, and the one at the rear door, three tones. You can couple the two circuits on the boards via terminal ‘C’. This may be useful in large premises because it enables both chimes to sound irrespective of which doorbell switch is pushed. In other words, the front door loud- speaker may produce a two-tone chime sound to indicate that the rear door needs answering.

Circuit Diagram

of Selective Door Chime Circuit

This amplifier can be designed using a few basic components. The circuit diagram of this project is shown below.

**Selective Door Chime Circuit Diagram**

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Working Explanation

of Selective Door Chime Circuit

The circuit is based on a three tones chime i.e. SAE0800 IC audio amplifier. The chime frequencies are determined by the oscillator frequency of the chip, which, in turn, depends on the value of the RC combination connect- ed to pins 5 and 6. The loudspeaker volume is set with a combination of a preset and a fixed resistor, P1 and R6 respectively, at pin 4.

Each board has a simple rectifier and regulator cir- cuit which allows it to be powered from an inexpensive a.c. mains adaptor. The quiescent current drain is about 5 mA. At maximum sound level (set with P1) this rises to about 400 mA.

If it is decided to link the front and rear door chimes, jumper JP1 has to be placed on both boards. Also, a cable with at least two wires must interconnect the ‘C’ and ground (‘0’) terminals of the two units. Alternatively, use a three-core cable, and feed the ‘++’ voltage of one unit to the ‘++’ terminal on the other. In that case, the rectifier on the daughter board may be omitted, since both units can be powered by a single mains adapter.

The loudspeaker should be a weather-resistant (if necessary) miniature type rated at about 1 watt.