IF i had a negitive supply i could sum the inputs
. but i don't have negitive supplys at hand
Most (all?) "rail to rail" op-amps, aren't. Close maybe, but still asymptotic. Only way to get 100% of a voltage range is for the supplies to exceed it.
Here's a circuit that should work with any 5V rail-to-rail output op amp.
.75-3 & doing in software doesn't cut it - you loose 1/4 the range ... no point in having 12 bits (4096 ) if you toss out 1/4 of them plenty of rail to rail single supply opamps /
i had tried today with a similar circuit / but to find out that i have to wait for smd holders for the proper opamp - 8dip ones i was trying with didn't have the bandwidth ...