This project sort of began with me wondering if you could eject "x" number of items from a hopper by powering / powering it fast enough. Unfortunately the best I could do was eject 48 items at a time. As I was intending to use this for a low tech tree solution to an automatic soul urn bottler, I decided to look into the possibility of using a turntable, rather than the conventional block detector.
Here is the result:
A turntable on the first setting constantly powers a singular block dispenser (a normal dispenser could be used from a side but I thought that once I employ this into my survival world, a dispenser from on top may be easier to automatically refill via hopper.)
A block dispenser counter contains 7 half slabs and 1 solid block. Upon this solid block being placed, the final ground netherrack is ejected and, after a short delay, the inverter powering the block dispenser responsible for urn placement, flashes, placing a new urn below.
It's fairly difficult to see from this angle (next image shows better), but sprouting off from the pulse extenders power supply, a repeater is facing a block. When receiving power, the redstone on the flip side of the block is powered, triggering my nether friendly item sweeper :)
( I removed encasing blocks to display this part properly)
This is probably my favourite bit of the setup, as it will work beautifully in the nether: as most of you can probably work out, the redstone current then retracts a sticky piston. This sticky piston is extended during the "dispenser firing" time, pushing forward a siding making sure no ground Nettherack nor concentrated hellfire leaps out anywhere. This withdraws just as the last piece of Nettherack is fired, on a slight delay, a piston on the opposite side then fires, wiping the soul sand hopper free of concentrated hellfire, and into the powered hopper that was revealed by the withdrawn siding.
*edit* DERP; picture
Cheers!