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Description 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...

For a lower parts count than the 2 transistor multivibrators, 2 LED s can be alternately flashed with a 555 integrated circuit configured as shown in Schematic 2.  I chose the combination of a 2K2 and a 47K resistor to determine the oscillation frequency along with the 10 uF capacitor connected to pins 2 and 6. You can practically change the (R Speed) 47K value to between 10K and 100K or more. Greater resistance = lower speed. You may also wish to connect up a 100K or so potentiometer instead of the 47K resistor for a variable speed version. Additionally, the 10 uF capacitor value can be changed. Feel free to experiment. Although, alternately flashing LED s  is great for the beginner to electronics, the basic one ON, one OFF circuit gets boring quickly. In the next section, we will try to improve the look and try to approximate a flash like a police car (within limits).

This LED flasher is based on 555 timer. One can use this flasher circuit either on bike/cycle or in police car!. The operating voltage of the circuit is 9v, but you can also use it at 6v.  Two sets of six LEDs are used here, but you can extend it to 40 each set. Flash cycle is determine by the RC time constant. However by using the pot you can set the flash rate of your choice. Transistor are used; to provide the additional current for leds and to switch the LEDs set at a time. Rest of the circuit is simple, no need to explain it; i guess. Now come to the circuit schematic. Schematic: LED Flasher Components Required: R1----------------------------4.7k ohm R3, R4-----------------------220 ohm R2 (VR1)---------------------150k or 220k pot R5-R10-----------------------100 ohm C1-----------------------------100nF Ceramic C2-----------------------------1uF/25v Electrolyte Q1-----------------------------BC547 Q2----------------------------BC557 D2-D7------------------------Blue LEDs D8-D...