IIRC, I used an RTD that I had left over from a 3D printer upgrade, but an 18B20 would fine as well. A 10K NTC resistor might even be good enough. For what I needed (and I think for what you need), just fixing the sensor to the outside of the pipe [if metal] will give you a usable signal. That sensor was just metal HVAC taped to the front cast iron door of the burner chamber.
But a dead-simple timer solution gets you pretty far as you know.
I have a mix of shame and pride that the chart (everything in the rectangle) is entirely hand-coded SVG elements emitted by the ESP web request handler.
IIRC, I used an RTD that I had left over from a 3D printer upgrade, but an 18B20 would fine as well. A 10K NTC resistor might even be good enough. For what I needed (and I think for what you need), just fixing the sensor to the outside of the pipe [if metal] will give you a usable signal. That sensor was just metal HVAC taped to the front cast iron door of the burner chamber.
But a dead-simple timer solution gets you pretty far as you know.