How to make fast blinking lights for bike

This is a fast blinking LED bike light circuit For safety when the bike at night. We use two-NPN-PNP transistor oscillator circuit and RC circuit only show on 4 LEDs use low current.

We take the four LEDs to parallel. Because of each LED use voltage about 3 – 4.5V
We want this circuit for a long time using so use the LED voltage is 3V only. And makes them blinking as the LED flasher.

Testing the LEDs in parallel

Figure 1 Testing the LEDs in parallel. They use current about 0.077A.
But we use them in switching so low

How this circuit works

This is a simple transistor oscillator circuit as a flip-flop. We use a simple RC. Here is the schematic of my two-transistor LED flasher: The RC circuit is connected to the base of the NPN transistor (2N3904) and it gives the signal to the PNP transistor (2N3906) to turn on the LED. When the PNP transistor is ON, it discharges the capacitor and it turns off itself, so the cycle repeats again.

Parts will you needs
Q1: 2N3904, Transistor General Purpose BJT NPN 40V 0.2A
Q2: 2N3906, Transistor General Purpose BJT PNP 40V 0.2A
C1: 22µF 25V, Electrolytic Capacitors
C2: 100µF 25V, Electrolytic Capacitors
R1: 330K, 1/4W Resistors tolerance: 5%
R2: 15 ohms, 1/4W Resistors tolerance: 5%
LED1-LED4, Color as you like
Battery, Switch, and more

How to build

Today I want tech my son assemble circuit on cardboard because he did not want to use PCB. We use the cardboard from old Desktop calendar that unused. We design the components layout on a paper. Then stick it on the cardboard with glue. As Figure 3

the layout on cardboard
Figure 3 the layout on cardboard

to use iron spikes holes to insert pins
Next step, to use iron spikes holes to insert pins as Figure 4

put the components on layout
And Then, put the components on layout as Figure 5

to use pin devices Or copper wire connected
After that, to use pin devices Or copper wire connected as Figure 6

Solder pins and copper wires to complete
Next, Solder pins and copper wires to complete. as Figure 7

Then, Test to use it as video below

And then,Apply glue pin devices, the access point and devices. In order to prevent vibration. As Figure 8
Apply glue pin devices

Last, To bring the circuit trial, mounted on a bicycle as Figure 9

and test it at night as video LED flasher good look and low current use.

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13 thoughts on “How to make fast blinking lights for bike”

  1. To anyone reading… I have a bunch of little electrical parts such as: transistors, diodes, led bulbs (white, red, and green). Jameco; Fairchild; lite -on; and so on. I really have no use for em and don’t know what they are really for. Everything is still new, never been used sealed in separate packages in quantities of 10pcs. If anyone interested in buying these from me please call me at 415 724 7358.

  2. Great circuit in which I am planning on making, but before I do, I was wondering what is the wattage of the 15 ohm resistor in the circuit?
    It looks like a 1/2 watt resistor, am I right?
    Thanks for the help and your contributions to those in the community that share the same interest in electronics.


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