Hi Everyone, Earlier I asked about Wood Stove controllers, and showed some working examples of reading high temperatures with Thermocouples (HERE). I'm still working on that but another project has taken priority.
The more complex project is for the design and construction of a electrically-heated kiln for making "Warm Glass", which is glass heated until pieces fuse together or "slump" or "drape" over shaped molds. This requires a careful profile of kiln temperature over a multi-section sequence of heating, "soaking" at a high temperature, rapid cooling to an intermediate temperature, annealing to stabilize stresses, and finally cooling to room temperature.
I would like feedback on what you see on the project progress so far. Comments/suggestions/critique welcome. I also am trying to make the project description page show some techniques of construction of a system like this. It's a big step for many people to go from a desktop prototype to a packaged system, and I get many questions (and see many here) about the problems in making a more complex system. There are both electrical challenges like Common Ground Point and mechanical challenges like cutting rectangular holes accurately in metal. Then there's mounting/packaging Arduinos and many peripheral modules. And cabling. So I'd also appreciate comments/suggestions/critique on that aspect: hopefully a practical example of making stuff like this. Lately I have been mostly making kits and writing how-to for relative newbies and younger people, and it's been a while since I've done a project like this.
So, my project page is HERE and I hope you may have time to look it over.
AND I have stuff I don't know how to do yet, and I'm asking for suggestions/pointers:
The active multi-level temperature control will use Brett's great Arduino PID library. I am getting to understand it a little, but this specific situation requires not just a PID approach to a single temperature, but control that follows a needed profile of temperature rate-of-change. So I THINK it's like "do a PID to the next intermediate setpoint in the next minute, then go to the next setpoint along the profile path". Or something like that. Anyone seen an example of doing that kind of control??
I need to initiate a read of a small text file on the PC into a buffer in the Arduino Mega. I didn't find a good example of that yet? Seen one??
I have seen/done some datalogging. But here I need logging over several hours, and hopefully nice graphing on the PC of Temperature vs Time. Any pointers??
I would LIKE to keep backing up critical parameters including "where in a firing schedule sequence I am" with the hope of being able to recover from a crash without destroying the Product in Process. I assume I can save this kind of information in EEPROM memory. Anyone seen example(s) of this crash/recovery/restart function?
I will put the CodeOfTheMoment on another page HERE
So far quite a bit of stuff is working. The one temporary disaster was the attempt I made to use a couple of small optically-isolated 30A relays to turn the main 240V power on and off. I have the main power cable (8-3 copper) wired to a 50 Amp outlet I use for a welder and plasma cutter. Hmmmm... What Could Go Wrong? Last night after dark I finally plugged that big plug in and flipped the 50 Amp breaker. BLAM!! FLASH!! ALL THE LIGHTS WENT OUT!! Jeezum Crow! (A Vermontism).. I stumbled blindly to the shop door where I knew the backup flashlight was. Got it. UNplugged The Project. No lights on in the house at all. Hmmm.. Went to the main breaker panel. Main breaker is ON (cycled it) but no lights. Doggone! There is another 100 Amp breaker, out on the power pole. In a locked box. In the Snow. Fortunately I had compulsively marked and tagged and hung up the KEY next to the panel. Flashlight out the door, through the snow, unlock the box, Cycle the breaker.. Lights!!
This was easily the most spectacular failure I've had in the past 20 years. Impressed my wife, too.
I read something about modern project management and agile development. "Fail Early" was one idea. Got That. That little relay was Way Overdone Toast. I have a real one coming from Digikey.
UPDATE I removed the toast and put in a temporary fuseblock with two 1/2 amp fuses. Plugged that big cord back in.. .. Flipped the breaker and.. the pilot lights came on, the power monitor showed 242 volts at 0.12 amps and the little (failsafe) temperature controller came up. It complained the Thermocouple was bad(gone) so I made a quick 6 inch long one with a propane torch and a hammer weld. OK for now..