Today I upgraded the Mass Flow Controller (MFC):
Previously I used a 9V battery + a potentiometer as a quick hack to control the MFC.
For the sake of fewer parts I wanted to remove the battery from the circuit. The power supply for the MFC provides +15V, which is way over the 0 to +5V I need to control the MFC.
To prevent over voltage I used a TVS diode which shorts to ground above +6V.
It seems to all work! Don’t have to worry about a dead battery now.
The hard part is the craftsmanship needed so it won’t short out. Work in progress: