Clever design, Andrew. Congrats. I'm curious about the cost of this compared to conventional technology. Is the cost higher? Are there some applications that would need this extra precision at any cost?
If you bought all the parts new, it would cost you about $30 to make. Depending on where you live, it might take a couple of years to get that back, but your comfort level will be greatly improved. The circuit can be made to be much more precise if needed. I'd replace the SCR power supply with a zener diode circuit or added an electronic regulator. This would only be needed if you used the thermal air pump to pull air through the box. If you used an isolated 24 volt power supply, the temp sensor could be brought outside the box, eliminating the need for the thermal air pump and any kind of regulated power supply.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.