This easy to construct “Handy pen torch” electronic circuit and low component count, uses two power white LEDs for lighting. Low volt (4.8V dc) supply available from the built in rechargeable Ni-Cd ...

The 555 circuit below is a flashing bicycle light powered with four C,D or AA cells (6 volts). Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second using RC values shown ...