Hourly Chime & Switch Using 555

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In this tutorial, we making a very interesting project of an Hourly chime & switch using 555 timer IC. This circuit is adjustable and can also be called a 555 alarm clock, it will produce an hourly beep or time signal after every hour and the LED will light up with each signal. It can be adjusted from a few minutes up to 1 and a half hours.

This circuit is very useful and can be used for different purposes like you can use it in quizzes and other competitions and adjust it to give a signal at the preset time (after every 5 to 10 minutes or more). In the place of the LED, you can also use a relay switch and connect any AC or DC device like a big alarm or bell. Figure 2 is showing a circuit with a relay switch.

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Hardware Components

The following components are required to make Hourly Chime & Switch Circuit

S.no	Component	Value	Qty
1.	DC Supply	4.5-12 V	1
2.	Relay	–	1
3.	Electrolytic Capacitor	1000µF	1
4.	Variable Resistor	5M	1
5.	Resistor	1KΩ, 470Ω	3, 1
6.	Transistor	2N4401	1
7.	IC	NE555 timer	1
8.	Diode	1N4148	2
9.	LED	–	1
10.	Piezo buzzer	–	1

NE555 IC Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 555 Timer

2N4401 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401

Hourly Chime & Switch Circuit

Working Explanation

This circuit can be operated at 4.5 to 12 volts DC. It is built around the 555 timer IC. Two diodes are used for the rectification of the input signal before going into the 5555 IC. We set the time period of the signals by adjusting the 5M variable resistor. It adjusts the gap between the time signals from a few seconds to 1.5 hours. This time gap can be increased by increasing the value of the 1000uF capacitor. The IC will give a high signal for the preset time period and the LED and the buzzer will be turned on. A transistor is used to amplify the audio of the piezo buzzer.