I have a Raspberry Pi 2 Model B and I am wondering if there is a pre-made solution, if I have to make it myself, or if it isn't an issue. For my project, the GPIO pins will be in constant use as inputs to check whether there is a signal or not, and the circuit that sends signals to the GPIOs can still send signals to the pi while it is off as it is not ran off of the pi. The circuit is a 6.3 VAC signal being converted to roughly 3.3 VDC following the diagram below.
There are multiple AC sources but they have a common ground (not the pi). I have 20 inputs to the GPIO, each either ~3v3 (but not over) or 0. I am planning to order a custom PCB so I can edit as needed.