Flashing LED Circuit using 555 timer ic

A Circuit that flashes an LED on and off. 

Overview 

This circuit uses the 555 timer in an Astable operating mode which generates a continuous output via Pin 3 in the form of a square wave. This turns the LED (D1) on and off. The speed at which the LED (D1) is turned on and off is set by the values of R1 and R2. 

Schematic 


Guys ,check out the follwoing video for its working:
http://www.youtube.com/watch?feature=player_embedded&v=bJa0oiV6B24

Astable mode will be discussed in the session.
for further queries,comment below

AUTOMATIC STREET LIGHT

Requirements

• LDR Light Dependent Resistor
• Take 2 transistors. (NPN transistor- BC547 or  BC548)
• Resistor- 1K, 330Ohm-2
• Light emitting diode (LED) - Any color
• Connecting wires- Use single-core plastic-coated wire of 0.6mm diameter (the standard size)-You can use wire that is used for Computer Networking.
• Power supply-6V or 9V

Procedure

• Insert first transistor Q1-BC548 (NPN) on breadboard (or general PCB) as shown in the circuit diagram 1.
• Connect another transistor Q2- BC548 (NPN) on breadboard as in step 1.
• Connect  wires across emitter pin of both transistors and –ve terminal of battery (lowest/ bottom row of breadboard.)
• Connect  a wire across Collector pin of transistor Q1 and Base pin of transistor Q2.
• Connect a resistor 1K across positive terminal of battery (topmost row of breadboard) and Collector pin of transistor Q1.
• Connect  Light Dependent Resistor (LDR) across positive terminal of battery (topmost row of breadboard) and base terminal of transistor Q1.
• insert a resistor- 330 Ohm across base pin of transistor Q1 and negative terminal of battery (lowest bottom row of breadboard).
• Connect a resistor 330R across positive terminal of battery (topmost row of breadboard) and anode terminal of LED (Light emitting diode) & Connect the cathode terminal of LED to Collector pin of transistor Q2.

The simple circuit is ready for testing now. Connect 6V battery terminals to the circuit as show in figand see the output. As you block light falling on Light dependent resistor (LDR), the LED glows.

LED GLOWS EVEN IN LESS DARKNESS. Use torch light or Lighter if the LED glows in less darkness. in addition, you can try to adjust the sensitivity of this circuit by using a variable resistor in place of R1-300Ohm. Try this circuit with other resistances as well, (e.g, 1KΩ, 10KΩ and 100KΩ, etc)

 

Circuit Diagram 1.Automatic Street Light Control System.(Sensor using LDR & Transistor BC 547.) Very Simple.  We have tried this one in this tutorial bu you can also try the second one

Circuit Diagram 2 .Automatic Street Light Control System.(Sensor using LDR & Transistor BC 547/ BC548.) Very Simple.

astable multivibrator mode of 555 timer ic

IC555 operating modes

IC555 has three different operating modes. These operating modes actually correspond to three different multivibrator configurations. 

     1.  Astable mode – it is also known as self triggering or free running mode. It has no stable state. It has two quasi stable states that automatically changes from one to another. It changes from high to low state and low to high state without any trigger input after pre determine time. This mode is used to generate square wave oscillations, clock pulse, PWM wave etc.

     2.   Monostable mode – it is also known as single shot mode. It has one stable state and one quasi stable state. It jumps into quasi stable state from stable state when trigger input is applied and comes back to stable state after pre determine time automatically. It is used in generating pulses, time delay etc.

      3.   Bistable mode – it is also known as flip-flop mode. It has both stable states. Two different trigger inputs are applied to change the state from high to low and low to high. It is used in automatic switching applications, to generate pulse of variable time etc.

frfrequncy modulation can be done using astable multivibrator mode of 555 timer 

8^th and 1^st pin of the 555 are used for giving power, Vcc and GND respectively. 4^th pin is the Reset pin which is a active low input, since it is tied to Vcc. When the output is high, capacitor C1 charges to Vcc through R1 and D. When the output is low, capacitor discharges through resistor R2 and 7^thof the IC. This charging and discharging time periods determines the time period of output. Message signal is fed to 5^th (Control Voltage) pin of the IC through a coupling capacitor and the output can be taken from the 3^ed pin of the IC.