Thank you so much for the detailed responses. One (hopefully) simple question i can never tell what grounds to common up. For instance, in that second picture it indicates a +vcc (5v) but doesn't show where -vcc is. On some of my EWB tests i've used the same ground for everything, my 10mV input (from a sig gen) and my comparator suppy i've been putting to the same ground point, is this incorrect? cheers