LED FLASHER WITH ONE TRANSISTOR
This is a novel flasher circuit using a single driver transistor that takes its flash-rate from a flashing LED. The flasher in the photo is 3mm. An ordinary LED will not work.
The flash rate cannot be altered by the brightness of the high-bright white LED can be adjusted by altering the 1k resistor across the 100u electrolytic to 4k7 or 10k.
The 1k resistor discharges the 100u so that when the transistor turns on, the charging current into the 100u illuminates the white LED.
If a 10k discharge resistor is used, the 100u is not fully discharged and the LED does not flash as bright.
All the parts in the photo are in the same places as in the circuit diagram to make it easy to see how the parts are connected.
source : http://www.talkingelectronics.com.au/projects/200TrCcts/200TrCcts.html