This post presents circuit for blinking two LEDs alternatively using two BC547 transistors. This circuit is commonly called a flip flop LED flasher. Generally used in alarm systems to produce flashing lights effect.
|1.||Power supply (3V – 5V)||1|
|5.||100μF electrolytic capacitor||2|
The blinking rate of the LEDs can be increased or decreased by changing the values of R2, R3 resistors, and C1, C2 capacitors. The frequency of a flashing LEDs can be calculated by given formula:
If R2, R3 resistors (R2=R3=R) and C1, C2 capacitors (C1=C2=C) have identical values then frequency can be calculated as follows:
The values of resistors are specified in ohms (Ω), values of capacitors are specified in farads (F).
By using values given in the circuit diagram (R2=R3=10kΩ and C1=C2=100μF), the frequency is about 0.72Hz and a time period is 1.386 seconds.
Circuit is designed on a breadboard.