Simple blinkers.

Simple blinker or flasher. No fancy ic's (integrated circuits) are required. Perfect for robots.

Transistor: (NPN)
2n3904

For an alternate light blinker (like at a railroad crossing) you might try:

Blink lights on the parallel port.
#!/bin/bash
echo "infinite loops [ hit CTRL+C to stop]"
for (( ; ; ))
do
   sudo parcon 1h2h3h4h5h6h7h8h
   pause 1
   sudo parcon 1l2l3l4l5l6l7l8l
   pause 1
done