In the real world they sell a "carbon doser" based primarily on a 555 timing chip and a Clippard mouse solenoid.
Like the concept and Theatrus has attempted (probably succeeded but proj appears dormant) to duplicate it here:
Micro solenoids for CO2 regulators - Reef Central Online Community
It dawned on me that using PWM and a MOSFET seems a somewhat similar concept but not the same...
Being mostly electronic basics idiot.. that may, in effect be what the 555 chip does but looking for alternates to skin a catfish..
Basic concept would be to control the PWM "duration" as usual. (bubble size)
Change the PWM dwell (on time) using a change in frequency. (bps)
All fed to a MOSFET to run a Clippard.
Advantage is w/ the right chip I believe one could eliminate the MOSFET
The above chip could output up to a 6w coil (?) giving one a one chip board..
excuse the ignorance of this but a Thurs thought
Addendum: Looking at the output waveforms.. seems one could "log" the output.. i.e like a slow ramp up in CO2.. ramp down..
does any of this make sense to anyone?