First thing is the temperature sensor, arguably the most important part to calibrate. I just get a value from 0 to 1024, the meaning of which is mainly determined by the 1K resistor I put across the thermistor.
At first, the PWM is giving trouble, not heating. But measuring the stepper motor driver heatsinks is interesting: X is pretty cool (34º), Y is really hot (95º), Z is pretty hot (70º), and EX is medium (90º)
Turns out I had misread the wiring markings on the heater. Now it heats, but slowly when I pause the heating to do measurements. I should rather go for a number of specific readings and hold each of those for a while with a little hysteresis.
But first, I need to get the thermistor properly connected. The little wires next to the extruder are hard to get on a connector, so I soldered some larger wire on, and now at least it seems solid.
Looked a bit more at the little thermistor print board, and realized I only had the GND and 5V connections, where I should have GND, 5V and a measurement. Fixed that (with a fixed-mount measurement wire), and now I get reasonable temperature numbers.
Raised the Z stage to see if I could get better temperature measurements.
According to the hand-held thermometer, I have the following measurements:
55º at 680
64º at 800
75º at 890
90º at 900
At 900, the remaining plastic started flowing out - I don't think that happens at 90º.
When cooling down:
68º at 825
69º at 760