Just set something up like this-
R - redstone
P> - redstone repeater going ->
P< - redstone repeater going <-
T - redstone torch (break right after you put it down)
D - dispenser(s)
R-P>-P>-P>-R
PV PV
PV PV
T- R-R<-R<-R<-R-D
PearlCrafter (talk) 23:12, 25 February 2014 (UTC)