With -15V at one end of a potential divider and +5v at the other with equal resistors you will get -10V on the arduino's input.
something like this?:
CV POT PIN
7.5 2.5 5
5 2.5 3.75
2.5 2.5 2.5
0 2.5 1.25
-2.5 2.5 0
what i am unsure of, is the BAT46 diode. it says it has a forward voltage drop of 0.25v
(http://nl.mouser.com/ProductDetail/STMicroelectronics/BAT46/?qs=sGAEpiMZZMuIUjt4yeP9c4vDnG6dExKEZObNAFndhYk%3D). does this mean that the voltage on the microcontroler pin will always stay under 5.25V?
if i understand correctly this is what this "lsimaster" is saying over here:
CCS :: View topic - ADC input protection ?? (second post from the top).
i know you explain things here: Protection, thanks for that!
but i want to use the protection as a functional thing. so it will be protecting almost all the time if i send in a waveform that is clipping.. but in the datasheet of the atmega it says it can handle 5.5v and -0.5v but don't go to these voltages to often, because then it "may effect device reliability" (see text on image above) . so if i go to 5.25V and -0.25v allot will this be bad? it is over the standard voltage 5v and under the absolute maximum of 5.5V..