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Not electronics but who knows where to ask: anti-fog, anti-frost clear material?
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mortrek:
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.
themadhippy:
wot about a usb soldering iron as the heat source,might finally find something useful to do with them,and a small fan
nali:
Is this a still or video camera? If still, could a mechanical wiper or shutter work?

Note that you'll also probably need to consider dew as well as frost depending on environment https://en.wikipedia.org/wiki/Dew_point


mortrek:
I'm using a still camera. A mechanical wiper would probably not work because the ice would form regardless. A mechanical shutter is an interesting idea but I have no idea how to implement it. It would likely lock up from ice exposure, for example. The interior needs to be kept sealed from the outdoors for the equipment inside to have any chance of surviving a year outside, so a shutter would have to be exterior, and my head starts spinning a bit from the challenges introduced by it.

Not to keep bumping this topic... but I've got some ideas/a loose plan.

I ordered a 20W 12V infrared halogen 35-degree angle flood bulb originally meant for saunas. I will see if that is an efficient way to melt the ice. I will likely add at least one additional parallel bank of batteries, as well. It will detect freezing conditions with the DS3231, turn on the bulb for some time that will need to be figured out, and hopefully focus the energy effectively enough to clear the ice. Once the ice melts, presumably the hydrophilic surface will spread it out and the viewport area will be optically clear enough for a photo.

Of course, one or many of these things may not work out. I may just have to implement solar heating or something, which makes my project much less flexible.

I'll also need some sort of test environment, since it won't be freezing at night forever where I live. Maybe I'll just toss the thing in the freezer...
Kleinstein:
I mechanical shutter (on the outside)  may still be a good option.  Even if it would not stop the icing all the way, it could reduce the ice and could help reducing the heat needed to clear the rest, as less heat is lost. For the shutter one could consider a rotating disk with a hole - possibly transparent, so that failure would not block the sight totally.

Already having a kind of tube for shade can help, as there would be less air movement and less dirt. Chances are the window would not be the coldest part and ice would form at the tube instead of the glass. A colder part can catch the water before it reaches the window.
Icing is often bad on parts that get especially cold in the night - e.g. the roof of the car that looses radiative heat to the sky.

For the heater it could help to check if there is actually ice. There can be quite some days below zero without icing.

Depending on the lens and distance, some local spots may not be so bad, if the window is rather close to the lens. The dirt that is way out of focus (e.g. on the cameras front lens) with no light from behind does not show up very much. So not sure if the hydrophobic surface is actually so bad.
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