I have what looks like a similar oven I use for reflow. It has heating elements above and below the racks. I have a single sheet of aluminum in the middle position to hold my circuit board being reflowed. I use a thermocouple attached to a chunk of circuit board, screwed to the aluminum tray. I don't have a door actuator, but rely on me being there to open it during the cool-down cycle.
I'm never going to run this thing when I'm not physically present, but the door actuator seemed prudent based on the experience a buddy of mine had with his oven. He found that his oven doesn't cool fast enough during the "cool" parts of the cycle, to track the temperature profile well. He could only get the cooling to be fast enough by opening the door.
My controller is an arduino-style "ItsyBitsy M0", and it drives an optoisolated SSR between the wall power and the oven power cable.
Hmmm... opto-isolation, that's probably a good idea. I should do that. Glad you mentioned that.
My oven is un-modified, and I found that the heating and cooling rates with the heater 100% on and off were pretty close to the desired profile.
Gotcha. Other than the door actuator (and adding thermocouples), I don't plan to modify the core of the oven itself. It's all about switching the power on and off as needed through the SSR.
I have an auto-learning program that adjusts the on and off timing to hit my targets after a few calibration runs. There is no fancy PID loop or proportional heat control, it's just on and off.
I thought about going that route as well, but this is as much a didactic exercise for me as it is just a tool building exercise, and I've always wanted to learn more about control theory, so I think I'm going to go the PID route. Although once all the "pieces" are in place (thermocouples, door actuator, SSR), then I can tweak everything else through software, so I may experiment with different algorithms and approaches as I learn more about control theory.
I have the electronics in a small aluminum chassis, with a couple of buttons and a display, and I can control it with those. I also have a USB serial-port interface which lets me control the thing from a program running on a PC -- this gives me nice charting and logging. I also have duty-cycle heater control capability, and sometimes use that if I want to use the oven for medium-temperature thermal testing, but for soldering the on/off heater control works well. Duty-cycle control would only slow down the heating ramp, and it's already barely fast enough.
Sounds pretty close to what I'm planning. I definitely want to support data logging / control via a PC. I might use wifi for the connection instead of a USB cable though. Heck, I could even experiment with using Bluetooth, I suppose.
That said, I like the idea of having a display and some sort of input mechanism right on the oven... at the very least I'd like a way to select which temperature profile to run, a "start" and "stop" button, and a display of the instantaneous temperature in the oven.
That's an interesting thought about using the oven for thermal testing, and possibly other uses, besides just for soldering. I hadn't even considered it having any application besides soldering (and learning control theory stuff).