Sat nav day/night screens ..

[Jethro_uk]

Anyone know what they work by ?

[Harry Bloomfield]

on 02/10/2018, Jethro_uk supposed :

They get the time from the gps sats, they know where they are and from that can determine sunrise and sunset - so at those times they can use different screen colours for bright and dim, or in fact dim the actual brightness of the LCD.

[Tim Watts]

Time for the most part IME - I've not observed a purpose built GPS switch screen modes in a long tunnel for example.

[Vir Campestris]

You mean the way they switch?

I've always assumed that having an accurate clock and position looking up the local sunset time is trivial. I usually turn my lights on by it.

Andy

[Brian Gaff]

Must be one of them Bonnie Tyler sat navs. Keep telling you to turn around and every now and then they fall apart. Could your answer be as simple as the bloomin clock? Brian

[Halmyre]

My Garmin does switch in some tunnels.

[Andy Burns]

Mine works off a light sensor, e.g driving through an under pass can dim/reverse the colours.

[Tim Streater]

So does mine.

[alan_m]

My dedicated Tomtom and the Tomtom app on the phone both seemed to use the time of day to adjust (possibly based on time, date and location) although the setting could be user overridden.

The SatNav inbuilt to my car reacts to the light level and will change when going through a tunnel.

[Jethro_uk]

Thanks for the comments, and guesses at what I meant ...

I was indeed wondering how the sat nav (in this case it's an inbuilt one, but I have seen the same behaviour with a Garmin, and my phone-as-sat-nav, which suggests there's some common software somewhere ????)

... wondering how the sat nav knows what time to switch ?

I don't think it's photocell triggered, as yesterday I saw it happen at

08:12 - about 15 minutes after the auto-lights had turned off. But looking at the almanac, sunrise was 07:10 ???

I guess there's an experiment to be done placing all 3 units on, and seeing if they switched simultaneously (suggesting common software) or varied (suggesting something else) ?

Incidentally, all 3 dim when going into tunnels - and I'm pretty certain there's no photocell on the Garmin.

I asked this query here, because googling "how do sat navs day/night screens know when to switch" bought up a useless combination of ads for satnavs *with* a day/night feature, combined with articles on "how does a sat nav work". Notice the lack of any "intelligence" in parsing the query, let along "artificial" intelligence.

[GB]

The rear view mirror in my car has a sensor, so I wouldn't be surprised if that is used to dim other items.

[T i m]

My Garmin Nuvi does both.

Cheers, T i m

[T i m]

As did mine yesterday, 3 times (inc Dartford and a couple more on the M25).

Cheers, T i m

[T i m]

My Garmin Nuvi 'inverted' (Night mode) 3 times on the M25 yesterday whilst going though tunnels so it would have to (also) be a light sensor on that model (fairly new Nuvi).

Cheers, T i m

[Harry Bloomfield]

T i m formulated the question :

It could simply be basing the decision on knowing where it was and that it was in a tunnel based on its maps.

My built in satnav, before I replaced it was rather clever. In tunnels where there was no sat reception, it would use the ABS sensors to determine where it was inside the tunnel, plus some sort of giro system.

[DerbyBorn]

and I'm pretty

I Googled the same and got some good responses. What is wrong with your Googling?

[Brian Gaff]

When you are in a tunnel, noo time from the sats is there. After all it would be pretty easy to do it from a clock knowing the time zone and region and monitor the sat signals. Brian

[Vir Campestris]

There's a tunnel under Baden-Baden in Germany. We went through it with my Tom-tom. It was amazingly accurate all the way through - within 50 metres by the end.

Without ABS sensors of course. I suppose it _may_ have an accelerometer, but I'll be surprised. This would be the only use for it.

Andy

[JoeJoe]

Don't think Tom Tom has anything like that - their hardware is typically

10 years out of date.

Much more likely that it simply continues to move along the map inside the tunnel at the same average speed that you entered it.

[Andy Burns]

Andy Burns wrote

And mine now appears to have stopped switching (it can be set to day/night/auto in the menu) I noticed yesterday it was in "dark mode" mid afternoon ... maybe some birdshit on the sensor?