I built one basically the hardest way possible.
There’s a lot of debate about what “magic” the Cannatrol has. I talked to David/his salesman about his machine at Cannacon here in Albuquerque and noted the differences and similarities to what I’ve been playing with.
Last season I dried using a constant-VPD method based on independent thought and research about how to best dry plant material. This essential controls the “rate” of water removal. Cannatrol uses a slightly different method of fixing the dew-point, or absolute humidity. This controls the end state moisture of the product but less so the rate of water removal. If both setups are stable, they function equivilently when programmed with the same settings, although the two techniques differ slightly in reality.
In general I noted that his targets are a bit more aggressive than what I used (VPD=0.7kPA), resulting in predictably shorter drying times.
This season I’m going to modify the software to accomodate a two-stage drying/curing process. Initially, I’m going to dry the buds using constant-VPD (0.6-0.8kPa), say for a week. For week two I’ll transition to fixed absolute humidity (8-9g/cubic meter).
You can do all this with Inkbirds, although if you want to accomplish the cannatrol goal of fixed absolute humidity (this is the real meaning of dewpoint - the same as saying “controlled dew point”) you need to adjust the two settings based on each other. For example, if your drying space is hotter, you need a different RH setpoint.
Cannatrol you set a dewpoint. It’s easy to make a calculator that tells you the RH setpoint for a given temperature and dewpoint (or absolute humidity).
Here’s my machine.