I've done some DIY C02 generators in the past, but I've always put them in the hoop houses. I've never really known if they provided any real benefit, but I knew they did produce some gas, because if I pinched the straw I could feel the pressure building.
In you haven't read my interview with Eddy, view it here. In it he details how he used CO2, was well as other things, to grow a 2255 pound pumpkin last year. This year I decided to try something new. I put my DIY CO2 generator and put it in my grow closet (standard closet with grow lights in it that I use to start my plants). For the first time today, I put a CO2 sensor in my closet and was pleasantly suprised withe the results. My ambient, outdoor CO2 after calibrating was 360ppm (awe, the fresh mountain air). Typical would be around 400ppm. In my grow closet right now it is 858ppm. So that CO2 generator is doing its job with nearly double the CO2. I'll be putting these same CO2 generators in the hoop houses.
Eddy says he targets around 900ppm. Most professional growers will typically target 1000-1500ppm.
How do you make a CO2 generator. There are lots of great videos on youtube, but it is easy. I just take a milk jug and drill a hole in the cap so a straw would snuggly put int he hole. I then glued around the edge of the hole after inserting the straw. Put some warm water, a cup of sugar and some yeast in the jug. It will foam up sometimes, so don't put more than 1/3 of container full of the mixture. It doesn't take long for that yeast to start breaking down those sugars and for CO2 to start generating. Mix the container daily to help keep it going longer.