Co2 ppm, Air Temp, Res Level monitor/controller

Hey here is a little controller i built, because there wasnt any on the market that fit my need, and i was too cheap to buy a co2 controller... even tho this son of gun cost me 3x what a factory built one would by the time i ended up with a properly working unit.

This controller will :
Monitor and control Co2 ppm from 0ppm - 10,000ppm, and will turn on and off a Co2 regulator based on your Co2ppm and Dead Band Settings.
Monitor your air temp inside your grow room from -50F - +200F. (Well beyond what is normal )
If running a hydroponic system, this unit will monitor your reservoir level via a float sensor installed onto the side of your reservoir or mounted to your water pump.

The Dead Band setting incase you are not familiar with Dead Bands it is an area of a co2 range where no action occurs. IE: If you set your Co2 set to 1200ppm and have a Dead Band setting of 100ppm. The controller will allow the Co2 ppm to drop to 1100ppm before bringing back on the co2 reg. Then shut the reg back off again at 1200ppm or greater. This is important so you do not short cycle your Co2 Reg which means to turn it on and off multiple times and hour. Witch can cause premature failure.

As well as monitor and control co2, temp and res level, This unit also has a built in clock for keeping track of the time of day. Its very useful if you are like me and keep a physical written log of PH, Temp, Res level, Co2 and nute solution PPM.

== See exactly how this thing works here! ==

also none of this uses the adruino uno or any shield, its all put onto 1 solid board made from eagle cad with the arduino chip running solo with a 16Mhz crystal and a cpl caps.


  1. Relay/SSR for lighting control -or- a photosensor to detect lighting... elevated CO2 is wasted if there's no metabolism occurring.. with this much effort, you might as well maximize the efficiency by handling the lighting integration. The "dead band" logic you are talking about is referred to as "PID" in some circles, that type of programming is an art unto itself.. there's a well-done PID library for Arduino out there, you might want to look at it, if even to see how someone else came at the problem of using digital means to control analog processes...

  2. Serial output of the collected data.. keep a rolling buffer of data (you should be able to make the data pretty small with a little creative use of int/char) that you can connect to the unit and download the buffered data. Make the data comma-delimited, so you can import it directly into spreadsheets. A query/response via serial is easy enough, and this will save you pencils and grief. Alternatively, you could add an SD card and log the data to the card... which is probably the better option. You could store months of data on an SD card, even if taken at pretty tight intervals.

  3. Recently read an article (may have been Nature or SciAm) on CO2 and hydroculture, and a recent trend of using CO2 for pest control. The idea is that periodically, say every few days, the CO2 levels are taken VERY high for a few hours during night.. in the range of five to ten times the PPM you normally "enhance" the growing air to. Apparently the idea is to suffocate insects and eggs, and the level is apparently even enough to kill many fungi and things, as that kind of level throws a pH monkeywrench into almost anything's respiration... but green plants take it okay as long as it's only for a few hours. Neat idea, it has to be better than dangerous chemical insecticides, I would think. It seems such a great idea, maybe you can give it a try and let us know if it works!

Cute device, great job!

As an aside, in the same article, it spoke on using yeast as the generator for the CO2.. brewer's yeast and sugar is apparently a great way to "naturally" produce CO2, less costly and more environmentally friendly than cylinders. I would think that using yeast you'd have little danger of raising levels too high; though I suppose the only "regulator" would be a feed system for the sugar.. but that would take hours at least, I would think, to change the air CO2 concentration.. Just a thought, anyway :wink:

If I can find the article I'll post a link. Interesting read, was a really good discussion of the use of CO2 in greenhouse hydroculture and it's ups and downs. I'm sure you already know this (but I'll say it for the kids reading this), but please be careful.. Carbon Dioxide displaces "Normal" air and it's possible to actually black out and then subsequently perish if you make too big a mistake and walk into a room at some ridiculous level of CO2 concentration. I'd hate to hear a software glitch led to some tinkerer's untimely demise!

Haha yea i have allready had a cpl mistakes and dumped a 20 lbs tank into the room in a day n a half, the co2 is on a reg so it dosnt dump huge ammouts out at a time even if the selnoid valve is open, but its a waste of money.

I really like your data logging via serial idea, 2 days ago i ordered. a couple PH modules from phidgets and once i implement that i will DEF add data logging, ideally i would love to bring this thing to market. The fact that it has a resivor level sensor and alarm is SO HUGE, I have come home to a garden full of 75% dead plants due to a leak.

As far as pumping up the co2 levels 5x-10x to kill bugs i will for sure read up on because once you are half into bloom you cant really use any harsh chemicals to treat the plants due to it effecting the product.

thanks for your input and i will def read up on your suggestions