555 Timer IC

1. Definition

1.1 What is the 555 Timer?

The 555 Timer is one of the most popular integrated circuits ever made.
It can create timing and pulses in electronic circuits, like a stopwatch inside a chip.

It’s famous because it’s:

  • Easy to use.
  • Cheap.
  • Works with just a few extra parts (resistors and capacitors).

It can work in three basic modes:

  • Monostable : one pulse when triggered (like a camera shutter).
  • Astable : keeps pulsing on and off (like a blinking LED).
  • Bistable : stays on or off until told to change (like a light switch).

555 Timer

555 Timer Pinout

555 Timer pinout

2. Features

  • Works with supply voltages from 4.5V to 15V.
  • Can drive LEDs, speakers, or small motors directly (up to 200 mA).
  • Adjustable timing with resistors and capacitors.
  • Simple and cheap , great for learning electronics.

4. How to Use

Safety Note

If wired incorrectly, the IC can overheat or stop working. Always double-check your pin connections.

4.1 Pin functions

  1. GND : Ground (negative side of the power supply).
  2. TRIG : Starts the timing cycle when voltage drops below 1/3 of supply.
  3. OUT : Output pin (goes HIGH or LOW depending on timing).
  4. RESET : Resets the timer when pulled LOW (connect to VCC if not used).
  5. CTRL : Changes the internal voltage threshold (usually left unconnected).
  6. THR : Ends the timing cycle when voltage rises above 2/3 of supply.
  7. DISCH : Discharges the timing capacitor.
  8. VCC : Positive supply voltage.

4.2 Example: Blinking LED (Astable mode)

In astable mode, the 555 outputs a repeating ON-OFF signal.

Frequency formula:

f = 1.44 / (R1+2r2).C

Example:

  • R1 = 1 kΩ, R2 = 4.7 kΩ, C = 100 µF
  • Produces about 1 blink per second.

4.3 Example applications

  • LED blinkers and flashers.
  • Tone generators for buzzers.
  • Delay circuits (e.g., light turns off after a few seconds).
  • Simple PWM motor speed control.

5. Video Explanation

video coming soon