Alternating Flasher Diagram

This circuit uses three easily available 555 timer ICs. All three work as astable multivibrators. The first 555 has an on period and off period equal to 1 sec. This IC controls the on/ off periods of the other 2 555s which are used to flash two bulbs through the relay contacts.
The flashing occurs at a rate of 4 flashes per second.
The diodes are used to protect the 555 ICs from peaks. The relays should have an impedance greater than 50ohms i.e, they should not draw a current more than 200mA.
The flashing sequence is as follows:


The bulb(s) connected to the first relay flashes for about 1 sec at a rate of 4 flashes per second. Then the bulb(s) connected to the second relay flashes for 1 sec at a rate of 4 flashes per second. Then the cycle repeats.
The flashing rates can be varied by changing the capacitors C3 and C5. A higher value gives a lower flashing rate.
Note that the values of C3 and C5 should be equal and should be less than that of C1.
The value of C1 controls the change-over rate ( default 1sec). A higher value gives a lower change-over rate.
If you use the normally open contacts of the relay, on bulb will be OFF while other is flashing,and vice versa.
If normally closed contacts are used, one bulb will be ON while the other is flashing.

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LED Flasher Circuit Using 555 Timer IC

This is a simple LED flasher project that uses a common 555 timer IC for its operation. It is configured as an astable mode which means that its output is a square wave oscillator. Two LEDs are connected to its output in such a way that when one LED is ON, the other LED will turn OFF. 

It uses only 10 simple parts that are easily available at any electronic shops. Capacitor C2 charges exponentially through resistors R1, R2 and the resistance of the trimpot. When C2 has charged to about 2/3 VCC it stops charging and it discharges to about 1/3 VCC through R2 and the trimpot resistance via pin 7. This is the standard operation of a 555 timer. When a Vcc of 5 V to 15 V DC is applied to the circuit, the LED will start to flash.

The frequency of the flashing can be changed by varying the resistance of the potentiometer or trimpot.Parts List The parts list of the simple LED project is as shown below.

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