Here is a simple LED flasher for decoration purpose. The High bright LEDs flashes alternately giving a brilliant colour display. The circuit is a simple Astable multivibrator using two NPN transistors T1(left) and T2(right).The circuit works on the principle of charging and discharging of capacitors C1(left) and C2(right). Current from the positive of battery flows through first set of LEDs D1-D4(red LEDs) to the collector of T1 through resistor R1(100R left).
Resistor R1 limits current through the LEDs to protect them. The current through R1 and LEDs charge capacitor C1. It then discharges through the base of T2 and resistor R4(150k right). This gives base current to T2 and it conducts. As a result second set of LEDs D5-D8(green LEDs) lights. As the Capacitor C1 discharges completely, T2 turns off.LEDs D5-D8 also turns off.
The same thing happens in the other side also.This gives alternate flashing of LEDs.Thus the flashing effect is produced through the switching of T1 and T2 by the charge from capacitors.Flashing rate
can be changed by changing the value of R3,R4 or C1,C2. If 500K preset is used in the place of R3,R4, flashing rate can be varied.
