This week I got all the line voltage stuff working for the greenhouse controls. Reserc pump for hot water heating, 2 irrigation pumps, fans for venting. I still need to hook up the arduino controls for those, but it’s pretty simple since the SSRs are in place and the arduino can control those directly.
The load cells for measuring the weight of the plants have been giving me tons of trouble this week. About 10% of the time they work fine, calibrate, etc. But the other 90% of the time they just return garbage, like the conversion from data bits to floating point number is all screwed up. Or they just don’t read at all. Part of the problem was loose connections, I’d bump it and it would start or stop working. I ended up removing all the pin / breadboard like connections and soldering but still wouldn’t work. In the end I got 1 hx711 chip working consistently with a load cell giving reasonable data over the whole weekend. However, this chip was purchased from a different batch, so maybe I just have defective chips.
I also found that the hx711 chip is extremely temperature sensitive. Putting a finger on the chip or breathing on it changes the reading by up to 150g on a 50kg load cell. I was under the impression that the temperature sensitivity on load cells was the load cell itself, but that error seems to be dwarfed by the hx711 temperature dependence. I will try to keep the hx711 chips in a junction box under the hydroponic trays where the thermal mass of the soil will limit temperature swings.
I ordered some new load cells and hx711 chips in hope that that will solve the problem. In the meantime, next week I will work on getting the arduino actively controlling the greenhouse climate and insulated doors for the fan venting openings.
Sun Aquasystems 