Here the schematic diagram of Easy LED Flasher circuit:
Parts List:
| R1 = 10M ohm R2 = 1K – 100K ohm R3 = 470 ohm C1 = 0.47μF – 10μF/25V | D1 = 1N914 Q1 = 2N3904 Q2 = 2N3906 Led = High Brightness Red LED |
This circuit will flash a bright or high-brightness red LED (5000+ mcd). Very good for fake car alarm or other attention getting device. Part values are not significant, test something else to start with from your junkbox.Certainly, the 470 ohm resistor (R3) determines the LED's brightness and limits the current supply to around 20mA. R3 value of 390 ohm may also be applied as a save value.
If you decide to go using a green or yellow led, which take more current, you might want to change the 470 ohm with an suitable value. Flash speed is established by R2 and C1 and is roughly three time constants (3*R2*C1). R1 provides bias to Q1 which ought to be small enough not to saturate Q2 with the capacitor disconnected. When the circuit doesn't oscillate, R1 may be very low or R2 too high. D1 allows for highter duty cycle operation and limits the feedback at the base of Q1 to -0.7 volts. D1 might be ommited for low supply power like 6 - 9V and low duy cycle operation.