PID temperature controller, works!
Thought I'd post this in case anyone else is interested. I got this handy-dandy "PID" controller, it adjusts electrical output to a target heating (or cooling) device based on realtime feedback from a temperature probe. It took me a day to figure it out and get it set correctly, but it is now calibrated for the heating device I am using. For me, the controller only takes a few minutes to go from a room temp to the set-temp, and is accurate to appx +/- 0.5 degrees of the target temp. Most of the time it is spot-on. It has a nice feature of defining schedules in advance with 6 steps max. For example, if you want something to be held at 50C for 2 hours, then at 60C for 2 hours, you can pre-program it and walk away. Each step has a max of 9999 minutes. It has many ways to configure it, you can either set the P. I. D. values directly, or use a "Auto-Tune" feature (automatic calibration). Ultimately, I had to lower the max electrical output by 80% to my heater, effectively turning my 1000-watt burner into a 200-watt burner, then used the auto-tune, and it calibrated itself perfectly.
The controller was inexpensive, less than $200 USD. My heater is a cheap $15 single-coil burner from the local drugstore.
Here it is, holding a mash steady at 60C. (60.2C at the time I took the photo). The tip of the probe is metal (stainless steel I think..) and is submerged entirely in the mash.