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Alternating Flasher -Designed by Naveen P N Click here for the circuit 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
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
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
If normally closed contacts are used, one bulb will be ON while the
other is flashing.
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