I have a working but early stage project that controls solenoid valves. The solenoids are isolated via TIP120’s. At the moment I am using 2 separate power supplies. The first is a 12V supply for the solenoids and the second is a 9V supply for the Arduino Nano.
Can I use the 12V supply for the Arduino as well as the solenoids, make a connection from the power in straight to the Arduino vin, or should I add some kind of protection between power supply and Arduino?