I want to design a torch height controller for plasma cutters. Power for my controller will be coming from either a computers power supply or wall-wart and then run though TI dc/dc converter to output regulated 3.3v for mcu, relays and LEDs.
An output from the plasma cutter will be connected to an ADC pin on my mcu via a resistor divider and this output will vary from 0 - 7v DC (which indicates 50:1 ratio of plasma cutter ARC voltage). I need to read this voltage signal output from plasma cutter with my mcu so that I know when to respond with an appropriate action.
http://www.hypertherm.com/en-us/Products/Handheld_cutting/Systems/powermax45.jsp#6
Question is, can I connect the grounds of these two power supplies together without damaging anything or does my controller power supply need to be isolated?
Thank you.