Bed Heater Control Circuit & Software

I’m working on a project that needs a ‘pretty accurate’ heated panel, and so the first thing I thought of is the TAZ 6 print bed. I’ve dug around on the Lulzbot site and found some reference. The best thing I came up with is this pdf. It gives me the power requirement for the heater, and a part number for the Honeywell thermistor, but I am looking for more details on the rest of the circuit for the sensor and how to calibrate it. Honeywell has this page for it, and I’m familiar with Wein Bridge circuits but it would be nice to see how you folks are doing it and how to scale the sensor readings.

Also, I plan on using a PWM on the heater element with an off-the-shelf 24V/15A capable supply, thinking that a properly rated SSR will do the trick, but would like to see the circuit that you’re using. Is there a directory or repo that you could point me to?

I believe the Taz6 uses the Rambo v1.4 like the workhose. The schematic can be found in the link below. The board files are Altium but the board itself is a real basic Arduino derivative.

If temperature uniformity and accuracy is important across the build plate then you may want to pick up a FLIR camera and some thermal paste. I had an issue with one of the corners being colder than the rest. I’m waiting for a new toolhead before I do the experiment.

Depending on the magnitude of the desired accuracy a TEC might be a better option. They’re pretty easy to get down to a stable +/- 0.01C.