Wow! That is an impressive amount of work put into that. I'm posting a screenshot from your video so others can appreciate the complexity of at least the breadboard part -
All the lights, hoses, and gauges connected outside of the box are pretty impressive too.
I can't really tell exactly what is digital vs. analog as far as what goes where. It does look like you have maybe 8 analog signals being read by the Arduino itself. Just from my experience with much smaller
mixed projects, I'd strongly suspect you are getting a lot of signal noise on the power lines causing issues. And, on the video I saw the temperature reading jump up and down about 10° in a matter of seconds. If that's a rolling average with that large of swing....well.
You can think of the entire circuit as a complex system of thin, high-pressure water pipes with many outlet spigot/faucets throughout constantly being opened & closed at different frequencies. ...You already know how just a small leak can affect pressure.
Here is a few short articles which explain how power supply & circuit layout can affect analog signals & overall performance. http://www.eetimes.com/document.asp?doc_id=1272289http://www.analog.com/static/imported-f ... N-1103.pdf
I wouldn't even know where to begin turning your breadboard into a soldered PCB. But, I think your issue has less to do with contact/connection quality and a lot more to do with noisy/over-taxed power supply, signal 'crosstalk', and possibly even some other unwanted electrical phenomena from the breadboard and bundles of wires.
Are those graphs all from the data logger, or do you also have an oscilloscope? Exploring the different areas of your design with even a relatively inexpensive scope would possibly shock you and really help you understand what the individual signals really
look like. Instead of a smooth line or the nice square digital signals you see in datasheets, it probably looks more like the "Eng" line on your data graph. :o
• Trying to separate the the digital & analog power rails as much as possible and maybe using multiple regulated power supplies. (All grounds need to be connected, but things can be done to keep that somewhat isolated.)
•Look into using decoupling/bypass capacitors for each major component or group/section. The important considerations are noisy digital vs. quieter analog circuits & making sure larger power consumers (like the LCD) don't steal power from nearby components.
•Using the AREF pin (and add code to use it). The idea is to have the voltage at AREF match as closely as possible the exact voltage being used by the analog sensor device. That way any voltage fluctuations at the sensor are reflected at AREF, and the Arduino will use that as reference for measurement, keeping the readings much more accurate.
There are a lot of articles & resources about mixed signal circuit and power supply designs. Just google around. Analog.com is also full of great searchable technical reference.
Good luck! I may be watching for updates on your website...
Just for my own interest - When did you start building/using that Arduino sensor project?