MTH smoke units have no “brains” in them… they have a 4 wire interface, 2 for the fan, and 2 for the heater element.
All the puffing, etc, is handled by their MTH DCS decoder.
There are DCC decoders that will the same kind of control, like Zimo decoders.
In another category, are smoke units that have an input to control the fan and/or heater.
TAS used to make them, they got bought by Lionel, Massoth sells one, it has an input that you pulse to make it “puff”…
Yet another category are units with electronics that keep them from burning out, but just basically have a constant smoke output, normally somewhat more at higher voltages, like the Aristo unit.
Finally, there are the really dumb smoke units, that are just a heater that will burn out if you run it dry, like the stock LGB units, and the old Aristo units.
You want to so some more reading on these, it’s easy to get confused, especially since some are advertised in a somewhat misleading way.
You can read up a bit on my site:
http://www.elmassian.com/trains/dcc-battery-rc-electronics/smoke-units
Regards, Greg