During this lockdown I got the idea of using one of the unused inputs on my Davis weather station for a cloud detector. A thermopile detector of the sort used for infrared thermometers, when pointed at the night sky, does a fine job of sensing clouds: a clear sky has a temperature near absolute zero, while clouds have a much higher temperature.
One of the practical issues in a cloud sensor is keeping dew off of the detector. (Clearing away rain and snow is another concern, not addressed here.) To this end, it's good to heat the sensor just enough to maintain it at the ambient air temperature. The thermopile device already has a thermistor inside the can, because you have to know the device temperature to figure out the temperature of the object it's looking at. A similar thermistor facing the ground could be used to switch on a low-power heater whenever the upward-facing sensor drops below the temperature of the downward-facing sensor, with perhaps 1-2 degrees of extra safety margin.
The thermopile detector comes in a TO-style metal can. I'd like to find a resistor / heating element which I could thermally couple to the thermopile can and drive at ~ 1/4 watt. I have some really thin Nichrome wire, but it would be a pain to insulate, and the resistance still isn't high enough. Ordinary SMD resistors could, I suppose, have one end soldered to the can, but it would be even nicer if there were a "resistance thingie" with an isolated metal casing which could be soldered to the can. Anyone know if something like this exists?