This is a complementary relaxation oscillator based on two transistors. It can be used as a low current flashing pilot lamp for battery operated equipment where current conservation is essential.
The base bias for TR1 is provided by the the potential divider formed by R1/R2.The positive feedback capacitor C1 is 10uF. Any 20mA LED can be used.
The circuit's operating frequency depends upon a number of factors, such as, characteristics of transistors used; the value of capacitor and resistor C1, R2; and the DC voltage. With the default components values shown in the circuit schematic above, the flashing rate of the LED is about 1Hz and the duty cycle is about 30%.