# Compass on rear view mirror, power consumption



## RonArt (Mar 6, 2020)

Regular compasses don't seem to work in my car (too much metal?), so I want to replace the mirror with one that has a compass built in (different sensing method). The one I want takes <200mA to feed the compass, but I'm not sure if that means its memory or its display. Could I leave it plugged in to 12 volts at all times? 

There is a pin on the compass that senses when the ignition is on. So I think the display only comes on when the car is on. 

Again, could I leave it plugged in to 12 volts at all times? This way I could share the 12 volt line nearby, the one that feeds the dome light, without having to run a wire to sense the ignition state.


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## de-nagorg (Feb 23, 2014)

Probably can.

The only problem that I foresee, might be draining the battery, if it is weak, or you don't drive regularly, like months at a time that it is not ran.

Otherwise the draw is not very harmful, just remember that you need to run the vehicle often enough to keep the battery charged. 

The clock in the stereo, if you have one, is a draw also, as well as many of the electronic memories if you have a modern vehicle.


Most dome lights are only fed voltage when the door is ajar.
ED


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## RonArt (Mar 6, 2020)

Thank you for the timely response, de-nagorg. I do drive every day, rarely miss a day. The clock in the dashboard always shows the time in its LCD (not LED) display. Agreed regarding dome lights, but my car's don't work that way, there is no switch on either door, but you make a good point for the majority of vehicles. 

I'll give it a try then. My insurance does have a free jump start option. I'll only report back here if I end up needing that service, but it sounds like <200mA is going to take more than a weekend to drain the car's battery.


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## ron45 (Feb 25, 2014)

Find a fuse that is only on when the car is running and use it for the compass.

There's no problems that way.

Or.

You could go with your idea and install a toggle switch.

Camping world has good installers. I have used them to put electric, heaters/airconditioners, sockets and switches in V-nose utility trailers.
Flat tow packages on jeeps, Silverado 2500 HD crew cab.

Check 'em out.
Free estimates.


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## RonArt (Mar 6, 2020)

ron45, both of your suggestions would work. The first sounds a bit complicated plus it would require finding a way to manage the wire from the mirror to the fuse. The second is spot on for me. My car is very simple: no power windows or power door locks, plus I have to manually turn the lights off (not even a warning bell). So adding "turn the toggle switch off" to my shut-down routine is not a problem. I'll add the toggle switch (to whichever pin(s) is(are) used to signal the ignition status). So then the only "overnight" draw would be very minimal (to keep the compass from losing its bearing). Thanks!


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## lenaitch (Feb 10, 2014)

By the sounds of things your vehicle may be older, but if it is new and has a Body Control Module, tapping into a line used for something else may not be that straight forward.
Check to see if your aftermarket mirror/compass has an internal battery to maintain it's settings.
Compensating for the metal mass is do-able (calling 'swinging a compass') but it is unlikely that a dash-mounted aftermarket floating magnet automotive compass has the adjustment capability. Magnetic fields change as things turn on an off but the overriding impact is the large metal bits like body, engine, etc. Most vehicles with built-in compasses have a procedure in the owner's manual. Then again, it is unlikely most motorists need that level of accuracy and I'll bet most folks with a built-in compass have never bothered.


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## ukrkoz (Dec 31, 2010)

I leave dashcam plugged into hot 12V for days and it never drained anything. Yes, it stays on. I doubt it will drain anything, of you drive car and my truck is garage queen. Driven once every other week.


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## Mystriss (Dec 26, 2018)

Related: 

My dodge durango had a compass and temp reading on the rear view (really liked it btw) and it never had any trouble battery wise - even over the winter when it was 20-30*F below. Though to be fair, the transmission was NOT happy about being outside so after a few years we had decided she was an "indoor truck" heh


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## RonArt (Mar 6, 2020)

All great info/advice, lenaitch, ukrkoz, and Mystriss. Thanks. It's time to do it. There are a bunch to pick from online. The salvage yards may have some too, at lower prices.This is not an urgent issue, so results of my experience may be posted ?next month?.


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## MTN REMODEL LLC (Sep 11, 2010)

I don't actually know how much drain your battery can take....good that it is driven often.

However, my BMW 528 has an intrinsic problem common to all those BMW's...well documented, however it is a little different from yours.

BMW has numerous systems that slowly shut down (not immediate, as you can hear things shutting down 15 minutes after you shut it off....so it allready has a high drain on it.

But, from literature I've read , it should not have over 50 millamps draw when it is fully shut down....and if you expect 200 milliamp draw, that seems like alot to me. But you likely don't have the shut down draw either.

When used on numerous stop/start very short trips, it will run my battery down....never had a problem starting it, but when the battery gets low, it shuts off the clock/callender and shuts down the anti-hill and traction systems that come up on the dashboard...drive it a few miles and everything goes back to normal.


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## RonArt (Mar 6, 2020)

@MTN REMODEL LLC, so the BMW system accepts a 50mW long-term draw. Then, I'll take ron45's advice and add a toggle switch for the display. Should I forget to flip it off (no pun intended), then we'll see if the drain turns out to be a problem. I'm guessing the compass memory's draw is really small, but the display's draw is the issue.


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## MTN REMODEL LLC (Sep 11, 2010)

RonArt said:


> @MTN REMODEL LLC, so the BMW system accepts a 50mW I think you mean MAlong-term draw. Then, I'll take ron45's advice and add a toggle switch for the display. Should I forget to flip it off (no pun intended), then we'll see if the drain turns out to be a problem. I'm guessing the compass memory's draw is really small, but the display's draw is the issue.


I like your approach..... but I still "flip it off" (pun intended)

Matter of fact, there is a Chicago Tribune article with a guy bit__ching that he did not buy a 70K car that could not take repeated short trips.

BMW has corrected that since is my understanding.


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## RonArt (Mar 6, 2020)

You are correct, MTN REMODEL LLC, I should have said 50 mA (.050mA), not 50 mW (.050mW), which is 12V times .004166 amps . The term "toggle switch" also implies changing state with every touch. Just plain "on-off switch" would be a better choice (some have a "lever" making them look like cockpit switches). 

This could be a fun project. The follow-up would be a "wireless" rear view camera plugged into the cigarette lighter (so just one cable between the monitor on the dashboard and the lighter on the console). The "wireless" camera bleeds off the backup lights in the trunk when they are on. 

It's going to take some time to shut down this puppy. Turn the monitor off (check), turn the compass off (check), turn the radio off (check), turn the lights off (check), take the keys (check), lock the door (check). Whew.


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## de-nagorg (Feb 23, 2014)

RonArt said:


> You are correct, MTN REMODEL LLC, I should have said 50 mA (.050mA), not 50 mW (.050mW), which is 12V times .004166 amps . The term "toggle switch" also implies changing state with every touch. Just plain "on-off switch" would be a better choice (some have a "lever" making them look like cockpit switches).
> 
> This could be a fun project. The follow-up would be a "wireless" rear view camera plugged into the cigarette lighter (so just one cable between the monitor on the dashboard and the lighter on the console). The "wireless" camera bleeds off the backup lights in the trunk when they are on.
> 
> It's going to take some time to shut down this puppy. Turn the monitor off (check), turn the compass off (check), turn the radio off (check), turn the lights off (check), take the keys (check), lock the door (check). Whew.


Does your car have a sensor in the seat, where you need to be seated, before it will crank?

If so , use that as your "toggle" switch to activate the compass.

Not seated, no power to the ignition, and the compass.


ED


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## RonArt (Mar 6, 2020)

@de-negorg Thanks. While the seat switch idea is pretty clever -- I wouldn't have thought of it -- my car is super simple. Plus, my goal is to minimize the wires visible to the driver and passengers. I'm heading off to a salvage yard today. Whatever is available will influence how this rear view mirror gets implemented. 

I did order a rear view camera and monitor from Banggood last night ($37 USD incl shipping(. When it arrives, it will be quarantined for 2 weeks. I understand that previous viruses cannot survive over 9 days without a host. They don't carry mirrors with built-in compasses. Some on Amazon and eBay are quite expensive (>$100). "The collar is worth more than the dog!" -- old Spain-ish saying.


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## de-nagorg (Feb 23, 2014)

Every car that I have seen in the last 60 years , ( this includes those that are now 100 years old), had a trim piece that surrounded the inside of the windshield edge that a wire can be placed under to run down to the dash, and hidden behind there, and attached to the fuse panel.

ED


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## raylo32 (Nov 25, 2006)

My Toyota Tacoma has an OEM rear view mirror compass. You might could find one of these at a bone yard... although I am not sure the guts of the compass are in there. It might just be the display? There is an associated circuit board in the overhead. In any case, I don't find the compass to be all that useful as I usually have to go in the direction of the road I am on. ;-)


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## RonArt (Mar 6, 2020)

Again, this is the most stripped down car I have ever owned. It does not have any trim along the top of the windshield. I plan to remove the dome light housing and drill a hole to pass a cable through to the new mirror, and replace the housing with a switch installed. 

I have read that these mirrors use 3-axis to know which way is which (N, NE, etc.). One pin is for Ground, another for +12V to aliment (feed) the module in the mirror, and another +12V to signal that the ignition is turned on (this one will take the on-off switch). 

I think there is a City Ordinance here that no more than 2 blocks of road can be straight.


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## de-nagorg (Feb 23, 2014)

If you don't mind me asking, What kind of car is this.

A homemade dune buggy?


ED


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## de-nagorg (Feb 23, 2014)

raylo32 said:


> My Toyota Tacoma has an OEM rear view mirror compass. You might could find one of these at a bone yard... although I am not sure the guts of the compass are in there. It might just be the display? There is an associated circuit board in the overhead. In any case, I don't find the compass to be all that useful as I usually have to go in the direction of the road I am on. ;-)


For sure.

I must be different, I seem to have a magnet in my nose, I feel which way north is. 

Right now I am facing north. :biggrin2:


ED


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## lenaitch (Feb 10, 2014)

raylo32 said:


> My Toyota Tacoma has an OEM rear view mirror compass. You might could find one of these at a bone yard... although I am not sure the guts of the compass are in there. It might just be the display? There is an associated circuit board in the overhead. In any case, I don't find the compass to be all that useful as I *usually have to go in the direction of the road I am on. ;-)*



I was in a serious collision a week and a half ago. The county road I was on goes basically north for about 6 or 7 km then bends west. For some reason, the nominal direction of the entire road is officially identified as east/west, which conflicts with my statement to the police and insurance company. My response is deal with it.
I put compasses on a vehicle right up there with the air temperature gauge on my motorcycle. Like I need a gauge to tell me how hot or cold I am.


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## RonArt (Mar 6, 2020)

No, no problem although it doesn't change anything. It is a 2011 Hyundai Accent. But this particular model is really basic. While it does have an automatic transmission, rear window defrost lines, and a radio with CD and XM, that's where the "luxury" ends. The windows are manual. There are no remote door locks. No power seats. I'll attach pics as this project moves on.


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## Mystriss (Dec 26, 2018)

RonArt said:


> @de-negorg Thanks. While the seat switch idea is pretty clever -- I wouldn't have thought of it -- my car is super simple. Plus, my goal is to minimize the wires visible to the driver and passengers. I'm heading off to a salvage yard today. Whatever is available will influence how this rear view mirror gets implemented.
> 
> I did order a rear view camera and monitor from Banggood last night ($37 USD incl shipping(. When it arrives, it will be quarantined for 2 weeks. I understand that previous viruses cannot survive over 9 days without a host. They don't carry mirrors with built-in compasses. Some on Amazon and eBay are quite expensive (>$100). "The collar is worth more than the dog!" -- old Spain-ish saying.


Related: https://www.amazon.com/gp/product/B07L6FJGR4/ref=ppx_yo_dt_b_asin_title_o01_s01?ie=UTF8&psc=1

With that thing you can pop your roof panel/cover off and put the wires under it. My husband just ordered that kit and two other tools from them to replace the rear hatch panel on one of the boys' cars and they're pretty nice quality.


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## RonArt (Mar 6, 2020)

Well that was fairly easy. Below is a link to some before-and-after pictures. 

At a local auto salvage yard, I removed a rear view mirror with a builtin compass, dimming feature, and temperature. Cost $15 USD. 

At a local electronics shop, the SPST toggle switch cost $2 USD. 

The internet shows which pin is +12 volts and which is ground. That's all that's needed. The mirror has a capacitor that powers the circuit and also lets it remember the previous setting. The switch is only needed to light up the LED display. Turn the powered mirror slowly 3 times to set the bearing. 

Some notes: 
GND on mirror goes to ground on auto body.
+12v on mirror goes to switch, which then goes to +12 on dome lights. 
Dome (Courtesy) lights do not require ignition to be on. 
Car battery is 45 Ah (Amp Hours). Compass LED is 180 milliAmps. 
.18A times 48 hours = 8.64 AHs, in case the switch is not turned off in 2 days. 
OPTION: Use an ignition-activated +12v terminal to avoid the switch altogether. 
MAJOR CHALLENGE: marrying windshield's "button" (metal plate) to new mirror. 
Avoid a lot of trouble by buying a mirror with the same "shoe" type.

Link to pics on Google Drive:
https://drive.google.com/open?id=1gG8vDMpL4JECszW4lLvO9C-F0gAfIhQ7


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