Use an Etho Hopper Clock (plenty of videos on Youtube) with 48 items in it (at 2.5 items per second going between the hoppers, it will take 120 seconds, or two minutes, for all items to go back and forth), and connect one side side to a rising-edge monostable circuit (Mumbo Jumbo has good videos on those). Every 2 minutes, all the items will go from one hopper to the other, and it will toggle, and then that signal can simply be turned to a pulse by the monostable circuit. Hope this helps
with my melon farm. I've tried all of the clocks I've seen on youtube. The problem with the etho hopper clock. the Redstone block connects to my Redstone for the 2 minutes while it goes back into the other hopper. so, therefore. the pistons stay extended. so the melons cannot grow. i need a clock that will quickly send a pulse. then the Redstone line goes dead. so the pistons only extend for the 1 tick
@BoomBap: Only trick is that signal is normally on rather than off. A simple redstone torch corrects that problem though. Also be careful that when you're pulling the signal from there that you keep the redstone line pointing into the piston. If you had put the repeater say facing "down" (in relation to the screenshot) rather than right, it would break the clock.
Or yeah, use a monostable. One of the easiest and most flexible is a dropper facing into a hopper that faces back into the dropper, with a single item in the dropper. You can orient it in almost any direction you want (just can't have the dropper on top, since hoppers can't face upwards.) Run the redstone line into a block beside the dropper (don't run it into the dropper directly -- hard powering the dropper will lock the hopper and break the thing,) and a comparator coming out of either the dropper (if you want default-on and pulses off) or the hopper (if you want default-off and pulses on.)