Finally, some heat. Today I set up the induction heater described previously with some control circuitry including an ATtiny85, mosfet to switch the heater on and off, and a thermistor attached to the tube. I'll start by showing you the setup.

And here's the schematic.

The test was a partial success. Everything worked. The tube warmed up to about 150C in 30 seconds or so and would have continued on to the target of 180 if I had let it. But I saw a faint wisp of of smoke rising from the rectifier. Indeed the rectifier and the two mosfets in the heater were very hot. So I investigated and found that it was drawing around 6.5A with the tube which is more than double the current when I was heating a screwdriver. Although it is well within the specs of the parts, I will have to attach some hefty heat sinks before I try again.

More details - The tube is 16mm OD, 1mm thick steel. The thermistor is connected to very small coaxial cable as close as possible to the sensor to avoid any loops that the magnetic field could sneak through. The tube is wrapped in electrical tape and a small hole was cut in the tape for the thermistor and a small dab of thermal conducting grease. The thermistor was them wrapped in tape. Here are a couple more pictures.