Hi,
Here's a way with 8 sources, each one linked to a different midi note. They all use the same formula: trigger(midi.note(1, x+1)>0, 0.5, 0,100,0).
x is the horizontal position of the source. You can replace the x+1 by the midi note number you want or you can adjust it to track other midi note by changing the +1 value. For example, to track from midi note 40, you do +40.