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While getting started electronics it is good if you do some basic experiments related to 555 Timer IC. The basic experiment includes Automatic LED Blinking Circuit using 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.
1. IC 555 Timer 2. Resistor 1K - 2 nos 3. Resistor 470K - 1 nos 4. Electrolytic Capacitor 1 uf 5. LED 6. 9 volt Battery
Here is a circuit diagram of Automatic LED Blinking Circuit using 555 Timer IC. Assemble the circuit in breadboard and connect the power supply, LED will automatic starts blinking.
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.
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 of the Circuit:
555 timer IC is used here in astable operating mode which generates a continuous output in the form of square wave via pin 3 which turns the LED on and off. Once you connect battery in the circuit, it should flash the LED. If it doesn’t work, check the connections again.
Also make sure that battery is connected properly in the breadboard and power is reaching to the components of circuit. Here you can change the flashing speed of LED by changing the capacitor with different capacitance. If you want to add more LEDs in this flashing LED circuit, connect them parallel with the first LED using proper resistors.