555 timer Integrated Circuit

555 Timer IC

Complete Guide to the Most Popular Timer Circuit

What is 555 Timer IC?

The 555 timer IC is a widely used and highly reliable integrated circuit in the field of electronics. It is commonly used to produce accurate time delays, pulse generation, and oscillations. Whether you're building simple LED blinkers or more complex timing circuits, the 555 timer is an essential component. It was designed by Hans Camenzind and introduced by Signetics Corporation in 1971. Since then, it has become a fundamental building block for hobbyists, students, and professionals.

Why it is called 555 Timer IC?

The name "555" comes from the three 5k ohm resistors used inside the IC, forming a voltage divider network. These resistors play a crucial role in determining the reference voltage levels used by the internal comparators.

555 Timer IC Circuit Diagram

Internal Circuit

Pin Diagram

This is the pin diagram of the 555 timer IC. It follows an 8-pin Dual In-line Package (DIP) configuration.

555 Timer IC Pin Configuration

1. GND (Pin 1): Connect this to the ground (0V) of the power supply.

2. TRIG (Pin 2): Trigger input, used to start the timing cycle when the voltage drops below 1/3 of VCC.

3. OUT (Pin 3): Output pin, goes high or low depending on the mode and timing state.

4. RESET (Pin 4): Resets the timing operation when pulled low (connect to VCC if not used).

5. CTRL (Pin 5): Control voltage (optional), used to adjust threshold voltage levels (usually connected to a capacitor).

6. THR (Pin 6): Threshold input, ends the timing cycle when voltage exceeds 2/3 of VCC.

7. DIS (Pin 7): Discharge pin, used to discharge the timing capacitor to ground.

8. VCC (Pin 8): Power supply (typically from 4.5V to 15V).

Modes of 555 Timer IC

The 555 timer IC can operate in three main modes:

Monostable Mode

Bistable Mode

Astable Mode

Monostable Mode 555 Timer IC

Monostable mode is a one-shot pulse mode. In this mode, the 555 timer output stays LOW until a trigger input is given. Once triggered, the output goes HIGH for a specific time period and then returns to LOW. It's useful in applications like timers, pulse generation, and switch debouncing. A common example is a doorbell – press once, and the bell rings for a specific time regardless of how long you hold the button.

Circuit Diagram of Monostable Mode 555 Timer IC

Credit:- Monostable Mode Circuit Diagram / Electrosome

Bistable Mode 555 Timer IC

Bistable mode is similar to a flip-flop. The output stays in either a HIGH or LOW state until you press a switch to change it. It has two stable states, hence the name "bistable." This is like a toggle switch or a lamp with a push-button switch: press once to turn it ON, press again to turn it OFF.

Circuit Diagram of Bistable Mode 555 Timer IC

Credit:- Circuit Digest - Electronics Engineering News, Latest Products, Articles and Projects

Astable Mode 555 Timer IC

Astable mode continuously switches the output between HIGH and LOW, without requiring any external trigger. It's often used to create blinking lights, tone generators, and clock pulses. The timing is controlled by two resistors and a capacitor.

Circuit Diagram of Astable Mode 555 Timer IC

Credit:- 555 Timer Astable Oscillator Circuit - Engineering Calculators & Tools

Graph of All Modes of 555 Timer IC

Monostable Mode

Credit:- 555 Monostable | Electronics Club

Bistable Mode Graph

Since bistable mode does not involve automatic transitions or timed changes, it does not have a traditional timing graph. The output only changes when an input (set/reset) signal is given.

Astable Mode Graph

555 Timer IC Datasheet

Get the complete technical specifications and detailed information

Download Datasheet

Prices of 555 Timer IC

The price of a 555 timer IC generally ranges from ₹5 to ₹40 depending on the brand and supplier. It is often cheaper when purchased in bulk. You can find it at local electronics markets or components stores at a better price than online retailers.

Conclusion

Hope you found this blog informative. Feel free to comment below if you have any doubts or want a dedicated blog post on any specific mode in detail. I'd be happy to write it. Don't forget to like and share!