Dual LED Flasher circuit using PNP transistors

I like this dual LED flasher circuit. Two LEDs flash alternately. There are many ways to flash LEDs on and off using transistors. We may call it that Free Running Multivibrator. It works like Flip Flop that triggers itself repeatedly. It also demonstrates a very important kind of digital logic circuit, the a stable multivibrator.

First, see in the circuit below. There are ten components only. I think you do not need to know its principles very very deep. I just want to see you use it in an easy way.

Dual LED Flasher  using 2N2907

Four important things! you should know

First, Both Q1 and Q2 are general PNP transistors such as 2N3906,2N2907, BC558, etc. They are like switches on-off to drive two LEDs.

Second, R1 and R2 limit current to LEDs. If you use 9V battery, you can use them up to 1K, 3mm LEDs. In lower resistance will be high current, high lighting.

Third, R3 and R4 make a bias current to base of transistors to conduct current. They control the gain of amplifiers.

And important, they increase the time required to charge capacitors and speed up the discharged of capacitors.

Final, the Flash rate is easily changed simply by changing one, or both, of the timing capacitors C1 and C2. Reducing them will fast the flash rate. When they have different values, one LED will stay on longer than the other.

Hope friends have fun LED Flasher. This circuit has plenty of fun and practical application.

Keep reading: ‘Two LED Flasher using Gate of IC 4011’ »

This circuit is working well on breadboard. below..

Update
There is the friend of mine want a PCB layout of this circuit. So I designed the PCB layout for You easy to builds this circuit as Figure below.

components-layout-of-dual-led-flasher-by-2n2907
The components layout of Dual LED Flasher using BC556 or BC557 or BC558

copper-layout-of-dual-led-flasher-by-2n2907
And An actual-size of Single-sided Copper PCB layout.

Keep reading: ‘Blinking two LEDs using transistor BC548’ »

11 Comments

  1. farid August 8, 2013 Reply
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