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Yesterday I was driving back from Scotland to England, doing 70ish, when we ran into a really heavy thunderstorm. Went from good visibility to almost zero in seconds, and the only thing I could properly see was the crash barrier alongside the lane. I found myself desperately trying to see where the road was, simultaneously trying not to get rear-ended as I slowed up, switch on the rear fog lamps and hazards, max wipers, and select max demist because suddenly the windscreen had fogged up. Was one of those thankfully-rare maximum mental workload moments. Thank god for manual controls and muscle memory. Pretty such I wouldn't have had enough spare attention and/or brainpower left over for operating a touchscreen.

Honest question: Why don't modern cars yet monitor humidity in and outside the car and make the correct decisions to keep your windows clear? Why are we focusing on self-driving cars while our cars are too dumb to do this much on their own?

It isn't caused by any specific humidity levels. While it is depositing water droplets on to the glass surface, that same water is normally suspended harmlessly in the air (it is effectively de-humidifying the air onto the cold windows).

It is caused by the glass's surface temperature being much lower than the air temperature inside the car. Humans are warm. The air we breath is warm. We're heating up the interior of the vehicle. When that warm air contacts the cold surface of the glass, the water droplets migrate from the air onto the surface.

In order to detect it you'd need to know the glass's surface temperature ideally in the middle (away from the car's body) and also know the interior temperature. The interior temp they already have. But figuring out the glass's temp is non-trivial. Infrared camera is the only thing I can imagine working (since a sensor wouldn't be transparent or wouldn't be replaced when the glass is) but that would likely give inaccurate readings due to the outside temperature.

Yes, but could we maybe get a decent approximation of the windshield temperature from interior temperature, exterior temperature, and speed? Combined with interior/exterior humidity (maybe these gauges might be the expensive/finicky part of this project?), we could calculate a probability of window fogging.

It doesn't have to be perfect -- we can have it just turn on the defrost whenever the probability of window fogging is >10% or something.

Could glue/epoxy a sensor right behind the centre mirror I’d think. It’s far enough from the defroster vents that it wouldn’t heat up quickly from the hot air.

You could do one of two things. First, a heated windshield like I believe some Landrovers have. It’s about $5000 to replace, last I heard, but it works. Second, a double pane windshield like house windows or some motorcycle helmet face shields. These work 100% of the time, but would definitely be more expensive as well.

Best car I had for window defrosting/demisting was a Ford Mondeo which had a fine-mesh heating element embedded. Super fast clearing. More expensive than regular glass but not $5000 by a long shot.

I had a Honda Accord with a cracked radiator.... It defrosted right quick, but idling it after it warmed up was very ungood. After the radiator was replaced defrost went back to normal.

You can get it for most Fords. It's one of my favorite features, and any car maker that caters to the more northern people should have that option.

When it's sort of cold, but not "ice on the car" cold, it works great as defogging. Way faster than waiting for the car to heat up. When there is ice on the car, you turn on the heaters and within a minute or two you can simply use your wipers to clear the window of ice.

But, figuring out if visibility is good through the windshield is still manifestly a much easier problem to solve than self-driving cars.

It's not super accurate, but most cars these days also have outside temperature. Add a humidity sensor inside and outside, and we have temperature and humidity inside and outside the car, which should give us enough information for a basic microcontroller to approximate the temperature differential across the glass and whether or not fog (or frost) is likely.

I think knowing the temperatures and such amounts to predicting the foggy state. Detecting it could look much different. Visual observation is obvious. With purpose built glass, perhaps one could look at electrical properties on the inside of the windshield. Maybe changes in the reflectivity of the glass could be used. Maybe some refractive index shenanigans?

This seems like a simpler route. Why not just a camera pointed at a test mark on the windshield that checks if it is visible through the glass?

Or simply look for reflectivity at an angle, like the recent HN story about the guy who implemented a touchscreen on his Macbook by adding a small mirror to the camera above the screen.

> In order to detect it you'd need to know the glass's surface temperature ideally in the middle (away from the car's body) and also know the interior temperature

Or, perhaps more simply, have an optical sensor that detects and reacts to the fogging itself sooner than a human would.

Wouldn't it be easier to point a camera at the windshield and detect a change in opacity? I would think that's a far easier problem to solve than, say, facial recognition.

But figuring out the glass's temp is non-trivial.

Not really. Many windshields already have elements embedded in them like the ultra-thin wire used for the AM radio antenna. Sensing temperature via the resistance of a wire like that is about as trivial as it gets.

What if the glass had some small heating applied to it constantly?

Complete waste of energy? Additional energy required for AC when it is hot?

Because when the sensor goes screwy I don't want my car to start flipping shit like the defroster on when it's not needed? Because manual controls make such automation totally unnecessary? Because even if the automated system were designed to be "fail safe", the state that's 'safe' is actually context dependent, therefore manual controls will be necessary anyway?

It ain't broke, so stop trying to 'fix' it.

The problem is the current solution doesn't work. Because trying to perfect those settings manually while driving in near zero visibility is scary and dangerous. And nobody even knows the correct settings to use! There are YouTube videos testing whether cold or warm air is the fastest way to defrost and/or defog your window, because nobody knows or remembers.

I honestly don't remember and my solution is "try both for a little bit while maintaining control of the car".

I just leave the defrost on when it's raining or cold regardless of whether my windshield is fogging. No need for an automated system and my windshield never fogs up.

it's really not that complicated, you just have to understand why condensation is happening in the first place. it's always because the glass is colder than the moist air it is touching. there are two strategies to deal with this: either blow air with very low relative humidity over the glass, or fix the temperature differential itself. if you're using the "blow dry air" strategy, you always want to turn on AC and at least some heat, as this will create low relative humidity.

now in the winter you can sometimes do better than this by fixing the temperature differential itself. you can either lower the windows or cool the entire interior by blowing air with no heat. in reality, most people don't actually want to drive around in the winter with windows down or no heat, so the best tolerable option is usually to do as above: turn on AC and heat.

in the summer you can also get fogging on the outside of the windows. just use your wipers for this.

>it's really not that complicated

After reading this I am still not sure which one to use. They seem to both work.

Both work, one is just faster than the other. The post you replied to seems to imply that cold air is better in the winter, but that is absolutely not my experience.

When I get in the car in the morning, the air is already cold. No amount of more cold air from the vents will clear that. What's making it fog up, is the moisture I'm exhaling. More cold air is not going to fix that unless I drive with all windows down. So the only reasonable option since AC don't work at low temperature, is waiting for the car to heat up.

tl;dr of my post: turn on AC and blast hot air at the windshield. if that doesn't work in the winter, open your windows. if it doesn't work in the summer, it's because the fog is on the outside of the windshield; use your wipers.

In my car there is a front window defrost button that turns on the a/c (to dehumidify) but also the heat. Dry warm air does the best to remove condensation.

Perfect the settings? I've never driven a modern car that can't do it perfectly well when you hit the demister button. You're well overthinking things.

Manual works just fine. I just drove clear across the Trans-Canadian Highway, east to west, in a car with manual controls and it all worked great. Your eyes stay on the road because sober people can reach out and grab objects, like knobs or buttons, without looking. If the matter of defrosting confuses you then maybe you should sit down in your car for five minutes and learn how the multi-ton machine works before attempting to operate it; you owe that much to the rest of society. Don't ruin a car just because you are too lazy to work a damn knob.

(Warm dry air evaporates water that's condensing on cold surfaces. That's very far from rocket science.)

One: I think we can discuss this without condescension for anyone who doesn't agree with you.

Two: You are making a false choice: Automatic settings need not replace manual ones. Essentially what we are talking about is a spot on the dial that says "auto" which you are free to not use, much like headlight controls on higher end cars.

In practice the introduction of high-tech options reduces the availability of the manual options as manufacturers seek to reduce costs. Touch screen AC controls don't supplement manual controls, they replace them. This leaves people without irrational infatuations with tech high and dry, hence why I'm annoyed at anybody who advocates for it. If you've been in the market for a new car recently you'd see what I mean. Considering the state of the automotive industry right now, I think my comment was gentle. The suggestion that defrosting windows should be a matter delegated to a computer because it's confusing made me roll my eyes so hard, I was nearly blinded.

But cars already have this. My 2014 Ford Edge has front/rear defrost/defog buttons and they work just fine. As "liability" said, the answer is warm, dry air which happily works for both the defrost and the defog requests.

Well, they worked fine, but my A/C just went out, so getting dehumidified air is a problem these days.

>It ain't broke, so stop trying to 'fix' it.

Sure, but the marketing department had to fill a few blanks in the "bad weather options pack" (optional but casually installed on all cars in production that will be available in the next six-eight months) for a mere US$ 3,000:

1) self-learning wipers (using AI to set automatically an appropriate wiping speed, including economode, that only wipes the right side of the windscreen when you make a free turn on right at a traffic light)

2) intelligent defrost (computing the correct defrost temperature through analysis of real-time satellite heat maps)

3) heated and ventilated mats (that can dry your wet shoes and lower half of trousers independently from heating/confitioning settings)

I hope you make an artistic statement and patent some of these awesome ideas. 1) for conversation starter purposes, and 2) so that we can make sure auto manufacturers never actually do this, or at least you get fabulously rich in the process...

Interesting this patent literally just expired today: https://patents.google.com/patent/US5412296

Expired in 2012, buddy.

oops, read that last line incorrectly, its more of a status than an event.

I'd rather have the AC system dehumidify outside air, then reheat it before blowing it on the inside of the windshield. Most car HVAC systems make AC and heat mutually exclusive.

Dry hot air to heat the windshield above the dew point avoids the "damned if you do, damned if you don't" choice of cold dry air to keep the inside from fogging up versus hot humid air to keep the outside from fogging up.

It's not a matter of temperature sensing on the windshield, but humidity sensing in the cabin air.

Automatics are great when they work. I do have automatic wipers, which usually work pretty well. Fortunately they didn't remove the manual controls though because I had a boat on the roof yesterday, and the rain sensor behind the rear-view mirror didn't really see as much rain as I did.

There is a max-demist button, which for me is the perfect automatic function - it says what I want, and lets the car get on with selecting max fan/heat/AC/flow to the demist vents. And I can find it with muscle memory when I need it.

This is the Airbus v Boeing problem. There are two schools of thought, one being that you the operator can control all the settings including the ones necessary to avoid the fogging. There are others that do so automatically. So many times people would be aggravated that my a/c would turn on with the heat in my Audi. What they didn’t realize was how that prevented fogging of the windows which inevitably would happen a few min later. I noticed my current car also does this but it turns itself on after the heat has kicked in.

Automatic things are annoying IF the user isn't sure what is happening or why.

Heat randomly turns on -> human is confused, maybe uncomfortable, and might think the car is broken/haunted.

Heat randomly turns on, car displays "Preventing windshield fogging" -> human is thankful car is thinking ahead.

Except that displaying unexpected content interrupts the driver’s attention and takes it way from where it needs to be.

It’s certainly not important enough to distract someone performing any delicate maneuver.

Thats why a good notification system comes in different levels. Like red and big for important messages, blue and small for information like "heating windshield".

> This is the Airbus v Boeing problem

This is a false dichotomy.

Why don't cars have 2 batteries? One for starting the car, and the other for all the crap that tends to kill the battery when you most need it?

Probably because it costs more money and nobody will pay for it. That's the best guess I have.

Some cars have do two batteries, one for start/stop and one for everything else. (For example, some Mercedes have these, Suzuki "mild hybrid" cars, etc.)

I know about the Mercedes but did not know about the Suzuki. My main point though is that this is not a feature in your bog standard Honda Civic or Toyota Corolla or Ford Fusion. I think it should be, it's a huge safety and convenience feature. That it is not in your average car implies it's probably too expensive for the utility it offers the average person.

Personally I solved the problem by buying a lithium ion car starter for both of our cars. Works great, but I really would prefer the cars just had some redundancy built in.

You just have to be picky when you choose cars; my twenty year old Land Cruiser came with twin batteries factory fitted - though rather than one for starting and one for all the thingamajigs, they went with two beefy ones in parallel - 2*105Ah makes sure it starts every time.

I have been contemplating using the second one as an auxiliary battery after installing a fridge in the boot, though. Basically a matter of fitting a voltage monitor and a hefty relay.

Two beefy ones in parallel don't really solve the problem. If you leave your 1-Amp (probably a gross underapproximation) headlights on over the course of ~200 hours, you'll deplete the battery.

-It doesn't solve the problem (which is why I am considering splitting them now that I have added a ~1A consumer to the mix), but it does postpone the problem for long enough to (in most cases) ensure that you will realise your mistake before it causes you not to be able to start your car.

Leaving the headlights on (~10A) as you leave the car in the evening will still let you start it in the morning, for example.

It's an add-on you can choose for cars, if you want to. A lot of service vehicles in Australia have 2 batteries for this reason. 1 for the vehicle, the second for chargers (USB, DC, etc), routers, fridges, cameras, etc.

Not around here. I've never seen it offered for a non top of the line luxury vehicle.

on the other hand, AC is one of the only electronic features that causes a meaningful hit to fuel economy (and available power, if you have a weak engine). I very much prefer to decide for myself when it turns on.

Your car likely already turns off the AC when you accelerate hard. Most of them do that.

But not at cruise, which op was alluding to

The difference is so minute that I don't see what the point could be.

Some cars do that automatically - in which case there are tons of complaints about the car turning on the climate control automatically. This is something where you just can't win...

they do but people resort to hyperbole all the time to justify their hatred of touch screen interfaces or just interfaces they do not like.

there are bad touch screen systems and there are good ones. just as there are badly laid out physical controls and good ones.

even muscle memory works with touch screens, to say otherwise is just a lie. however the biggest oversight people tend to ignore is, how little they actually interact with controls of their car other than the turn signals and such. Most modern cars have full climate controls which does include humidity and such, many have automatic lights and wipers, and some go as far as doing the driving.

nineteen to twenty four buttons on steering wheel is just fine and intuitive to some just like the same number on a center console yet these same people will complain about the simplicity of a properly design touch UI and fewer physical buttons as being too complex.

Rear fog lights: something more cars should have in the US for this exact situation.

Or fewer. The only time I ever see them on is when it's a clear night and I'm getting blinded by the person in front of me. That said, they are pretty useful for more than fog... They're good for flashing at people behind you who don't have their headlights on.

...a rear fog light is an additional parking light on the rear driver side of your car to help other cars identify the width of your car in foggy or other incline to weather situations. They are not brighter than any other light that would regularly be present on that car. If it is brighter and blinding as you say, rest assured the car has been illegally modified and is subject to constant harassment by police in all other jurisdictions!

In the all cars I've owned, rear fog light is brighter than regular rear lights. Not sure if they are brighter than braking lights, but brighter than "position" lights for sure.

https://content.icarcdn.com/styles/article_cover/s3/field/ar... http://www.waycoolinc.com/graphics/z3/03/052503/jt/P5250326....

I've owned three cars with rear fog lights and all of them came from the factory with the rear fog light(s) being brighter than the rear parking lights. That makes sense too -- because if rear parking lights were bright enough for fog then you wouldn't need rear fog lights.

In cases like this I love the radar cruise control in modern cars it very accurately shows what's ahead even when you can't see anything. Agree with your conclusion some of the latest luxury cars have touch screens and the UX is awful.

My radar cruise control, on a Mercedes, fails with heavy rainfall. Warns you to switch to visual control.

Eyesight on my Subaru would fail as well. Manual basically says “if you can’t see, that thing can’t see as well”. It uses two cameras after all as well.

My Volvo has touch controls for AC but physical buttons for quickly toggling windshield fans/demist. Feels like a decent compromise.

Honest question: why didn't you take the train? This would have been a good time to take another sip of your whisky and soda.

In the UK taking a train is often (but not always) more expensive than driving and can take longer too. Depending on the route there might not be a viable service. The service in bad weather isn’t very reliable either.

But for some routes it’s really easy and convenient. It just depends on where you are and where you’re going.

I didn't take the train because I was transporting my son's sailing boat back from a competition. Also the train line was flooded yesterday, so that wouldn't have been an option. But normally that's not a problem, and I agree, if I'm just transporting myself, I do like the train.

On Friday this happened https://www.bbc.co.uk/news/uk-49300025

British trains are very expensive and unreliable at the best of times. Anyone who can drive, does.

Because he didn't know the whether would be like that?

And because he already owns a car?

You know, when you take your drivers test in the US, you have to demonstrate your ability to know where all those functions are before you even pull away to start your test.

The real question, as I found yesterday, is can you switch on high-speed wipers, rear fog lights, hazard lights, and max-demist, in a few seconds, while you're devoting 99% of your brainpower to not crashing into an unseen vehicle slowing in front, not veering out of the lane that you can't really see, and glancing repeatedly in the mirror in case you're about to be rear-ended.

The question is not whether you can operate the controls under normal circumstances. It's whether you can do it when task-saturated with more important tasks. Under such circumstances, I simply wouldn't have had any attention left for glancing at a touchscreen, but I did know and could hit all the manual controls rapidly without looking.

The answer is you focus on dealing with what's in front of you, so turn on wipers and demist. If all the drivers do that, then no one needs to worry about what's happening behind them. After you take care of being able to see and control the car, then you worry about rear fogs and hazards.

And if it's really, really bad, pull over. Don't be like those idiots who decide to stop in the middle of a highway with 75mph traffic around them, under an overpass to protect themselves from a hailstorm.

This is like the arguments that C programmers just need to be more careful about errors. We know that people make mistakes, get distracted, and get older. Real engineering is about designing systems which work well in actual conditions, not some unrealistic ideal case assuming perfect conditions.

It’s also simply wrong: in California, I had to show use of turn signals – not anything else – and no other place I’ve driven since has ever made me pass a test again. Assuming that everyone reads the manual and practices with every new vehicle is unrealistic, so you’re looking at potentially half-century lags between what’s tested and what people are driving.

I always wondered if Californians know what turn signals are.

About as well as the rest of the country, with the possible exception of Maryland, where they’re used to decoy people by indicating the turn required by the lane you’re in as opposed to the turn three lanes over you’re actually going to make.

I actually wonder whether google maps / Waze integration would be a worthwhile improvement: self-driving cars are a good ways off but simply signaling the direction which the driver was just told to turn would be nice, and a majority of drivers seem to be using mapping apps these days.

It is by far the worst state (or province) I've lived in for lack of turn signal usage. I want to get a bumper sticker that says, "Your Turn Signal is Broken".

How about a bumper sticker that says, "I slow down for stop signs".

This depends on the state/region. There's no universal standard in the US, and some states definitely don't require the operation of all of these controls before the test.


Hmm, this doesn't seem to be a response to what I said. Maybe you accidentally replied to the wrong comment?

> you have to demonstrate your ability to know where all those functions are before you even pull away to start your test

if only s/he had to pass the same threshold to post on HN!

Even if that were true everywhere, people drive vehicles other than the one they used for their drivers test in their lifetime.

And just like when they learn to use the shifter, they need to learn what that thing on the other side of the steering wheel does too before driving off whether it's tested or not.

I commend you on your attention to detail under every circumstance, but not everyone masters the windshield defogger (to the point where they don’t have to look at it) the moment they sit down in a rental car.

This was not my experience in New York. You don’t have to demonstrate anything other than knowledge of where the turn signal, ignition, brake and gas pedal are.

I took a driver's test 3 years ago and this was not included.

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