# Transistor based LED flasher Circuits

Transistor based LED flasher circuits are commonly used in a variety of applications, including automotive lighting systems, alarms and security systems, medical equipment, and entertainment systems.

Here it is shown how to make one and two LED Flasher with 2N3904 general purpose transistor. This can be useful if you want to blink one or two LED if some event is detected. And so the LED flasher could be used to provide visual indication if something is detected. First one LED flasher circuit is illustrated and then two LED flasher circuit is illustrated.

### One LED flasher with Transistor

Here we will flash a LED with a general purpose transistor 2N3904. The following shows the circuit diagram of one LED based LED flasher.

The following shows the one led flasher circuit implemented on breadboard.

The rate at which the LED blinks is determined with the resister R3 and C2. The RC time constant is given by,

$$\tau = R_4 C_1 = 68K\Omega \times 10 \mu F = 1s$$

So the frequency of blinking led is,

$$f = \frac{1}{1s} = 1Hz$$

### Two LED flasher with Transistor

Next, the following circuit shows how to make a two LED flasher circuit with 2N3904 transistor.

The two led flasher circuit is just modification of the one led flasher circuit. We can just place another LED on the other side of the circuit.

The following shows the two led flasher circuit implemented on breadboard.

The working principle of the above led flasher circuit is based on the astable multivibrator circuit operation. This circuit works like an oscillator. Such principle of oscillation is also used in 555 Timer(555 Timer Oscillator Animation). Such led flasher circuit is useful and can be used with Light and Darkness sensor Circuit with LM393.

See the following video of animation and actual implementation of the transistor based LED flasher circuit.