Here is a very simple circuit of a LED flasher using a 2N2646 transistor. 2N2646 is a PN unijunction transistor or in short it is called UJT. The UJT transistor contains three pins, which are two bases and one emitter. In this circuit it is working as an oscillator with 10K resistor and 100uF capacitor.
The 390 ohms resistor is used to limit the current going to the transistor and the LED. The flashing frequency of the LED is depends on the value of R1 and C1. You have to make some little experiments with the values of R1 and C1 to make the desired flashing rate of the LED. For R1 you can use any value between 10K and 1M. You can also use a 1M variable resistor or potentiometer for R1. For C1 you can use any value between 1uF to 100uF. The circuit can be operated with 9 to 12V DC.
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