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Not electronics but who knows where to ask: anti-fog, anti-frost clear material?
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eliocor:
ever heard of Transparent Heater Windows?
Just some examples:
https://tfdinc.com/products/transparent-heaters/
http://www.visionteksystems.co.uk/transparent_heater_window.htm
https://diamondcoatings.com/ito-heater-windows/
https://abrisatechnologies.com/tech-notes/what-is-a-transparent-window-heater/
cdev:
Its my understanding from discussions here about OCXOs that most devices that need to generate heat in a very controllable and optimally energy efficient way use transistors to do it, not resistors.

There was one thread about a Bliley OCXO teardown where I think the use of transistors was discussed, perhaps in the thread about Lars Wallenius's simple GPSDO build.

 Sorry that I could not provide more info.


--- Quote from: mortrek on December 03, 2020, 06:19:59 pm ---I think there is genuinely no amount of current, accessible materials science that will solve my problem. Hydrophilic surface is great for fog, but terrible for frost. Hydrophobic is great in theory, but in practice just makes the viewport area filthy and doesn't really eliminate fog that well anyway.

I think my only choice is to use the hydrophilic coated viewport, and use some sort of heating to melt off frost.

I have two options (that I can come up with, anyway). First, use batteries to heat a focused part of the viewport, where I melt just enough for the lens view angle. I have  DS3231 connected to the uC, so I could probably just use the thermal data from that to tell if it's close to or below freezing. Then, whenever needed (possibly just once per day) I trigger a mosfet or relay or whatever to turn on a heating element that blows air onto the window. I would need to figure out how long this is necessary to melt the unknown thickness of ice on the window.

I do not have a heater that is compact enough to do this. It needs to be very small, have a fan, only consume maybe 1A, and run from 9V. Since I can't find this, I will try building my own from a fan and some power resistors w/heatsinks or nichrome or something. Probably the resistors, since they would be safer. So maybe a 10W heater with a fan. Hopefully this would not take too long to clear out a little frost.

Another option, which limits placement of the entire system, bulks it up and costs more, would be a solar cell connected to a mechanical thermostat that just runs a heating element inside the main rig as long as it receives power, possibly with a battery backup. It would likely stay above freezing much of the time, but that introduces not only the problems I already mentioned, but then the solar system becomes a whole issue to deal with in addition to everything else. I would like to be able to put my project in a wooded area, so solar dependency is not ideal.

So, for now, I'll experiment with the battery-based air heating system.

** What I could really use from someone is a source for a very small ~10w forced air low voltage (5-9V) heater. If such a thing doesn't just exist to buy, is there some sort of product that exists that I could cannibalize for parts? Like even cheapo heat guns are usually AC or, if low-voltage DC, are very high current devices. It needs to be very compact, the smaller the better. It's hard to specify an exact size, but something like less than 4cm cubed would be great, or even a form factor like a thick permanent marker would work.

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