This tutorial is about Tone Generator Doorbell Circuit using Dual IC 555 timers.
This circuit is simple and works well when button is pressed.
One IC works in astable mode and other in monostable mode.
It is very important for making sound to run a 8Ω speaker.
The circuit needs 9V DC power and makes nice sound to welcome the guests.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | ||
| 4.7k | 1 | |
| 10k | 1 | |
| 1k | 1 | |
| Preset 100k | 2 | |
| Capacitors | ||
| Ceramic 0.01µF | 3 | |
| Electrolytic 33µF 25V | 1 | |
| Electrolytic 100µF 25V | 1 | |
| Semiconductors | ||
| IC 555 Timer | 2 | |
| Push Button Switch | 1 | |
| Speaker 8Ω 1W | 1 |
This circuit uses two 555 timer ICs.
First one is IC1 which gives one pulse when switch is pressed.
Second one is IC2 it keeps turning ON and OFF and makes square wave.
When we press switch S1 it triggers IC1 at pin 2 and then pin 3 goes high for some time and is set by VR1 and VR2.
We can change sound by adjusting VR1 and VR2.
This pulse turns on IC2 and IC2 makes square wave signal.
Signal goes to 8 ohm speaker and this speaker makes sound while IC1 is active.
When IC1 time ends then IC2 stops and sound stops too.
Formulas with Calculations:
Formulas and simple calculations for Tone Generator Doorbell using 2 IC 555 timers:
IC1 monostable mode time:
T = 1.1 × VR1 × C1
where,
- T is the pulse time in seconds
- VR1 is 100k ohms
- C1 is 33µF
Calculation:
T = 1.1 × 100,000 × 33 × 10⁻⁶ = 3.63 sec
So sound lasts 3.63 seconds.
F = 1.44 / [(R2 + 2VR2) × C3]
where,
- F is the frequency in Hz
- R2 and VR2 are resistors in ohms
- C3 is the capacitor in farads
We can change R2, VR2 and C3 to get different tone and sound.
How to Build:
To build a Tone Generator Doorbell Circuit using Dual IC 555 Timers following steps need to be followed:
- Gather all parts shown in circuit diagram.
IC1 connections:
- Pin 1 connects to GND
- R1 and switch S1 connects from +V to GND
- Pin 2 connects between R1 and S1
- Pin 3 connects to pin 4 of IC2 and to resistor R2
- Pins 4 and 8 connects to +V
- Pin 5 connects to GND through C2
- Pin 6 connects to pin 7
- Pin 7 connects to one leg of VR1 and other leg of VR1 connects to +V
- C1 positive connects to pin 6 and C1 negative connects to GND
IC2 connections:
- Pin 1 connects to GND
- Pin 2 connects to pin 6
- Pin 3 connects to +ve of C5 and one end of 8Ω speaker
- C5 –ve connects to speaker and GND
- Pin 5 connects to GND through C4
- VR2 one leg connects to pin 7 and other leg connects to pin 6
- R3 one end connects to +V and other end connects to pin 7
- C3 connects between pin 2 and GND
- Pin 8 connects to +V
Conclusion:
This Tone Generator Doorbell Circuit using Dual IC 555 Timers is cheap and works well.
Monostable IC1 controls how long sound plays.
Astable IC2 controls how fast sound pulses.
Circuit is good project for beginners and it helps to learn how 555 timer can make sound.