How to Make a Blinking LED using a 555 Timer IC?

This article explains the circuit design for blinking LED using a 555 timer IC. This is a simple circuit designed to explain the working and use of a 555 timer IC. This circuit is designed using a low power consumption output device, a red LED. There are many applications of 555 timers, generally used in Lamp Dimmer, Wiper Speed control, Timer Switch, Variable duty cycle fixed frequency oscillator, PWM Modulation etc.

Blinking LED Circuit Using a 555 Timer IC

Circuit Components

• 555 timer IC
• LED
• 9V battery
• 1KΩ Resistor – 2
• 470KΩ Resistor
• 1µF Capacitor
• Bread Board
• Connecting wires

Circuit Diagram

The following circuit design explains the design of the blinking LED  (Light Emitting Diode) with the 555 timer IC. Here in this configuration, the 555 timer IC has connected in an Astable mode of 555 timer operation.

• Collect all the required components and place the 555 timer IC on the breadboard.
• Connect pin 1 of a 555 timer IC to the ground. You can find the pin structure of a 555 timer IC in the circuit diagram shown above.
• The longer lead of a polarized capacitor is the positive and the shorter lead is negative. Connect pin 2 to the positive end of a capacitor. Connect the negative lead of the capacitor to the ground of the battery.
• Now short the pin 2 to pin 6 of the 555 timer IC.
• Connect the output pin 3 with the positive lead of the LED using a 1kΩ resistor. The negative lead of LED needs to be connected with the ground.
• Connect pin 4 to the positive end of the battery.
• Pin 5 does not connect to anything.
• Connect pin 6 to pin 7 using a 470kΩ resistor.
• Connect pin 7 to the positive end of the battery using a 1kΩ resistor.
• Connect pin 8 to the positive end of the battery.
• Finally, connect the battery leads with the breadboard to start the power supply in the circuit.

Physical Diagram

555 timer IC is used to create time difference in various applications. The Blinking LED circuit uses a 555 timer in astable mode, which generates a continuous output in the form of a square wave at pin 3. This waveform will turn LED ON and OFF. The duration of ON/ OFF depends on the time cycle of the square wave. We can change the speed of blinking by changing the value of capacitance.

555 Timer IC

555 timer IC is the cheap, popular and precise timing device used in various applications. It gets the name from the three 5KΩ resistors that are used to generate two comparator reference voltages. This IC is operated as monostable, bistable or an astable multivibrator to produce a variety of applications.

This IC comes with bipolar 8 pins dual in-line package. It consists of 25 transistors, 2 diodes and 16 resistors arranged to form two comparators, flip-flops, and high current output stage.

Pin Description

The following is the pin description of the 555 timer IC.

Pin 1-Ground: It is connected to ground as usual. For the timer to function this pin should be connected to ground.

Pin 2-TRIGGER: The negative input comparator No 1. A negative pulse on this pin “sets” the internal Flip-flop when the voltage drops below 1/3Vcc causing the output to switch from a “LOW” to a “HIGH” state

Pin 3-OUTPUT: This pin also has no special function. This pin is drawn from PUSH-PULL configuration formed by transistors.This pin gives the output.

Pin 4-Reset: There is a flip-flop in the 555 IC timer chip. The output of flip-flop controls the chip output at pin 3 directly. This pin is connected to Vcc for the flip-flop to stop from hard resetting.

Pin 5-Control Pin: The control pin is connected from the negative input pin of comparator one. The function of this pin to give the user the direct control over the first comparator.

Pin 6-THRESHOLD: Threshold pin voltage determines when to reset the flip-flop in the timer. The threshold pin is drawn from positive input of comparator1.

Pin 7-DISCHARGE: The discharge pin is connected directly to the Collector of an internal NPN transistor which is used to “discharge” the timing capacitor to ground when the output at pin 3 switches “LOW”.

Pin 8-Power or VCC: This pin also has no special function. It is connected to a positive voltage.

Working Modes OF 555 Timer IC

The 555 timer IC operates in modes

• Astable mode
• Monostable mode
• Bistable mode

Astable mode

Astable mode means there will be no stable levels at the output. Thus the output will fluctuate from high and low. This character of the astable output is used as a clock or square wave output for many applications.

Features of 555 timer IC

• It operates from a wide range of power supplies ranging from + 5 Volts to + 18 Volts supply voltage.
• Sinking or sourcing 200 mA of load current.
• The external components should be selected properly so that the timing intervals can be done in several minutes along with the frequencies exceeding several hundred kiloHertz.
• The output of a 555 timer can drive a transistor-transistor logic (TTL) due to its high current output.
• It has a temperature stability of 50 parts per million (ppm) per degree Celsius change in temperature, or equivalently 0.005 %/ °C.
• The duty cycle of the timer is adjustable.
• The maximum power dissipation per package is 600 mW and its trigger and reset inputs has logic compatibility.

Thus, this is all about making of Blinking LED using a 555 timer IC. We hope that you have got a better understanding of this concept. Furthermore, any queries regarding this topic or 555 timer based projects, please give your valuable suggestions by commenting on the comment section below.