AO

I'm looking to install a GPS NAV system in my car sometime in the next few months. I was looking at a couple systems and they require it to be wired up to a speed sender.

I recall reading a long time ago that this was a problem for our cars. Does anyone know where one would tap for this?

There's a speed sender on the alarm system on the 91+. Would this work? (Term II)

John Krawczyk

Really? Why would the GPS unit need a speed sensor? I have a handheld Garmin that tells me the speed of anything holding it. I would have thought the only thing needed is a hot 12v lead and maybe a remote antennna.

Imo000

What happens when the tires start spining and the car is stationary?

BrettStrikes

My Magellan roadmate 700 tells me the speed I am going and the height above sea level at all times. This technology is at least three years old. I would have to believe the new indash GPS units must have the same technology. The speed is calculated based on the amount of time you take to pass through longitude and latitude. Signal is picked up by one of 7 satellites in orbit around the earth...which transmits those times into a calculated speed back to your GPS unit. It is dead nuts all the time....When I step on the gas there is a slight delay until the unit catches up to your speed...but on a constant highway speed...always matches my speedo...

docmirror

Minimum of three sats. Four for WAAS(augmented) service for altitude and location within about 30 meters.

Some of the high end units use a dead reconning system that can approximate your location with a speed sensor as discussed and an accurate time base(on the GPS unit). I don't know how they handle curves, but it would need to be inertial. I doubt they use that, so I'm guessing it's not very accurate, nor needed unless you drive in tunnels, or under bridges constantly.

AO

I'm looking at the just released JVC KD-NX5000. Single DIN with HDD based NAV.


I asked them to email me the manual and installation instructions, and all they would send me was the manual. In it it said I needed to have the speed sender signal. I don't know what it's used for, but I thought others had encountered this before. That all I know.

mnotz

I used to have a Blaupunkt Stereo that also had a GPS NAV system as an add-on in a 911 that I drove for a short time in '97 (I saw the light...was just not my ride! :-) ), and this system had additionally to the GPS antenna as far as I remember multiple speed sensors to aid in navigation when reception was bad or you were going through a tunnel, etc, as docmirror said through dead reckoning. Back then there was also no WAAS available yet, only differential GPS in the US, but not in Germany far away from the coast, so the accuracy was not great with plain GPS and the speed sensors made some difference there too.

I did not know that there are still systems out there that use speed sensors, but it makes sense, although my portable Garmin Streetpilot c340 is awesome and very accurate just plugged into a cigarette lighter and stuck on the windshield ;-)

Marcus.

Imo000

That's correct. Minimum 3 required but the more you can lock on the better the accuracy. Also there are 24 satelites in orbit and not 7.

TRUESCOTSMAN

If your looking for a pinout for the speed sensor, there is one on the abs psd unit. I think it is pin 16 but i will check it out. It is used in the 92 on cars as a take off for the speedo and goes to a relay that counts the pulses. On the uk cars the control unit is just above the ce box and it is quite easy to splice into it...... Jim

AO

Oh yeah! I believe that's under the driver seat in my car. Thanks... I 'll look up the pinouts.

AO

Found it. Thanks. Am posting for others.

PorKen

Cruise control connector.

928ntslow

The speed control hook up is essetial for internally fixed mounted units, not walkabout units. Thats why you will find it clearly states in your manual, that acuracy is within 4-6 feet depending on the unit. Is it necessary to be more accurate than that?...who know, who cares, but never the less, these hook ups are necessary for fixed units. Reverse and parking are necessary as well. Be informed also, that your walkabouts cannot compare to the power these fixed units have...unless of course you work for the USGS and have some incredibly expensive mobile GPS device. I have a NAVMAN which is quite powerful, but falls short compared to the power and information library of a fixed device.

This is out of the AVIC-D2 installation manual.

docmirror

I take it back, some of these high end units are indeed inertial at least partially. Useful when driving where sat reception is poor, and 4 sats cannot be resolved. Amazing what is being embedded in modern electronics. 25 years ago, inertial navigation was million dollar stuff.

The accuracy is gonna be resolved by a calculus of last position plus time base plus speed ticks plus inertial moments imparted. Drool......

heinrich

good choice Andrew