In my conversion I am using a 4X relay board that turns on and off the blower and compressor’s AC (no DC supply needed). This relay board is set up to interface to the smoothie when I am ready to control it from G/M code. It also can be controlled from the front panel.
I like this air pump very quiet with simple 1/4" air hose connections.(https://www.amazon.com/gp/product/B002JLGJVM/ref=oh_aui_search_detailpage?ie=UTF8&psc=1)
More info here: http://donsthings.blogspot.com/2016/11/the-k40-total-conversion.html
https://www.amazon.com/gp/product/B002JLGJVM/ref=oh_aui_search_detailpage?ie=UTF8&psc=1air