This will make an automatic dispenser that will flash rapidly.
***Do not attempt to make if certain flashing patterns could trigger a medical problem.***
Step 1: Items Needed
First add five redstone dust to the floor in a straight line like the picture above.
Add a lever to one side of the line of dust.
Add two blocks of smooth stone next to the third redstone dust. Then put redstone on top of the smooth stone blocks.
Next add redstone torches to the side of the stone going parallel with the line of dust. It will start to blink rapidly. When it's blinking just turn the lever to the off position.
Add a dispenser to the other side of the redstone line.
Fill up the dispenser with arrows and flip the lever.
Step 8: The Finishing Step
When the lever is flipped it should blink rapidly and shoot.