I'm making a circuit right now that uses an op-amp powered by a rail-splitter IC. The "virtual ground" created by the rail-splitter is 9V. i know Arduino analog inputs can only accept up to 5V, so my question is if Arduino's ground is connected to the virtual ground, is it safe to use? The voltage level in regards to the virtual ground will be around 1.5V (so 10.5V relative to 0V - but that shouldn't matter if Arduino's ground is connected to virtual ground, right?).
Same with a headphone jack - can I have the signal fluctuating around 9V when the jack/signal ground is connected to virtual ground?
Keep in mind, Arduino's actual ground has to be held at the virtual ground level and all voltages must be referenced to this ground. If ANY voltages or connections are referenced to the "true ground" they could kill the arduino. For example, your power connection will have to be referenced to the virtual ground (so ground=9V and power=14V).
Whatever your signal system is connected to, it is almost certain that things to which the Arduino will be connected, will actually be grounded and so would your "headphone jack".
It sounds as if you need a supply inverter - a switchmode device that provides a negative supply from a positive one. Can't recall seeing these on eBay as such but then of course, I haven't looked.
If you can guarantee the voltage to the input is within 0-5 volt relativ the aurdino ground you are safe.
If you draw a schematic it is MUCH more easier to say if it works or not. Paul B are sure it's a bad idea but how do he know?
You only need pen, paper and a camera.
Yes that will work providing the 9V source is floating with respect to the arduino's power supply. For example if the 9V came from a battery and the arduino's power came from USB or other power supply.
It wont be safe unless you protect the Arduino inputs - at power-up the opamps output could go anywhere
within its supply rails briefly. Also an analog signal below virtual ground will be negative from the Arduino's
PoV