This
is a classic 2 transistor astable multivibrator. Many other small signal
or switching transistors can be used, including 2N4401, PN2222 or 2N2222.
The circuit can also be inverted (don't invert the LEDs), and implemented
using PNP transistors such as 2N3906, 2N4403, PN2907, or 2N2907. The 470 ohm resistors determine the LED brightness. Lower resistance means higher current, and more light. LEDs that require more current or have a higher operating voltage (such as green and yellow) may work better with 300 ohms.
The RC time constant of the 39K ohms resistor and the 10uF capacitor determines the on time for each side. (The two sides do not need to match - vary the RC time constant for one side to get a lower or a higher duty cycle).
With the values shown, the flash rate is about 1 cycle per second.
|
Part
|
Quantity Needed
|
G&E Order Code
|
|
470ohms resistor
|
2 |
30.0210
|
|
39Kohms resistor
|
2
|
30.0440
|
|
10uF Capacitor
|
2
|
65.0060
|
|
Red LED
|
2
|
07.0740
|
|
2N3904
|
2
|
01.2N3904
|