please help me about this project. I want to make electronic bell. Which duration time is like

10.45 AM to 11.45 AM ..1st lecture 11.45 AM to 12.45 PM .. 2nd lecture

12.45 PM to 1.30 PM lunch break

1.30 PM to 2.30 PM .. 3rd lecture 2.30 PM to 3.30 PM .. 4th lecture 3.30 PM to 4.30 PM .. 5th lecture 4.30 PM to 5.30 PM ..last one

I want to make project based on IC 555 and decade counter. But I have no idea about this. Please help me guys how to make project for duration 1 hour .

  • 1
    \$\begingroup\$ This is a very bad idea. The 555 is not suitable for long times like that. Instead you need a real-time clock with a digital display and some buttons to allow editing of the ring times and bell duration. Use something like a Raspberry Pi instead. \$\endgroup\$ – Transistor Jul 14 '18 at 12:52

A 555 timer is totally inappropriate here. You want to trigger events at specific points in real time, and it sounds like you want this to run for days on end. A 555 timer simply doesn't have the accuracy required. Not even close.

Do the math. A 555 timer clock is derived from the values of a resistance and a capacitance. Typical resistors are good for 1% and capacitors for 10%, resulting in overall 11% accuracy.

Let's say you spend a lot of money and manage to get 2% accuracy overall. It should be obvious that this is still grossly inadequate. 2% error means 1.2 minutes drift each hour. If you started the timer at 10:00, then it would be off by 9 minutes by your last bell at 17:30. By the 10:45 bell the next morning, it would be off by 30 minutes. That would clearly make the device useless.

So how should this be done? Use a crystal for the timing component. Fortunately, accurate crystals for this purpose are readily and cheaply available due to the high volumes of the wristwatch industry. You can get 32.768 kHz crystals that are good to a few PPM (parts per million, 106). At 10 PPM, the error is less than half a minute/month, or less than a second per day. That should be acceptable for a class project.

You also need some logic that tracks the date and time of day. There are chips called real time clocks that do this, and that can even drive a 32.768 crystal directly.

However, you still need some additional logic anyway. All you really need is a small microcontroller. Most are also capable of driving a 32.768 kHz crystal and running from that directly, while drawing very little power. Just about any of the Microchip 16F parts with the "ELP" (extra low power) feature would be appropriate here, for example.

You can implement the real time clock function in firmware, then add your own logic of when to activate a bell and for how long.

Some microcontrollers even have real time clock hardware built in. This does the date and time of day generation from just a clock oscillator, and can usually trigger events tied to time of day. This is certainly not required, but it eliminates the need to implement this logic in firmware.


This is the way I would do it:

Major components required:

1) ESP8266

2) RTC module with battery backup

3) LCD display (optional but useful for showing time and other useful info)

4) Low voltage piezo buzzer if you want the sound to stay inside a room. A relay to connect a big bell if you want to notify a building

5) resistors, capacitors, a power supply, tact switches etc as per requirement

Thought process:

Hook up the RTC module to ESP using i2c lines. ESP should be programmed to connect your local wi fi and it should be configured to fetch time from some reliable time server on a button press (to correct time sync issues).

Use the display to show current time. Add a button which when pressed shows the next alarm time on the display.


Not the answer you're looking for? Browse other questions tagged or ask your own question.