jimmyblue

iTrader: (11)

I was asked about a way to fool a navigation unit to
think it's seeing a real, but acceptably low road speed.
Here is a notional circuit schematic using Radio Shack
parts. It pulses the VSS input low at about a 1Hz rate.
I don't know what the rate has to be, to make the
NAVI think you're in the parking lot; might have to
play with the timing capacitor (pin 6 to GND) some to
find what works.

todddchi

iTrader: (3)

My understanding has always been that the speed is calculated from the satellites, and the vss input is only used to supplement/average for hilly terrain or a bad satellite signal.

I didn't hook up my vss sensor, but couldn't you check to see if this method would work by just jacking the drive wheels up and generating a low speedo signal? I suspect the GPS would still show 0, unless there is no sat signal.

WhiteBird00

iTrader: (4)

The VSS provides 4000 pulses per mile so you can calculate your necessary pulse rate based on that (4000 pulses per minute @ 60MPH, 2000 pulses per minute @ 30MPH, etc.)

I assume you want this so that the controls aren't locked out. But doesn't fudging the speed input affect the NAV unit's normal navigation operation? Or does it independently calculate vehicle speed based on change of position over time? If that is the case, won't it still lock out the controls based on calculated speed regardless of the VSS signal? And if not, can't you just leave the VSS wire disconnected to show 0 MPH?

todddchi

iTrader: (3)

Also, a lot of Nav units can be used all the time just by grounding the brake wire. I just bought a new Kenwood unit that still has that workaround as an option. Though, I have heard that some of the nav units are now starting to use the gps readings to only take inputs while at 0mph.

What I don't understand, is why would you want to trick it into thinking it's moving?
Just curious.

Jpr5690

iTrader: (13)

no my stock navi\radio locks out menus while moving..

the idea here is to trick it into thinking your not moving or moving at under 5 mph.. just cutting the wire or grounding it dosent work for verry long as the computer faultsd and it starts back up using some other measure of vehicle spped to lock it out...

Jpr5690

iTrader: (13)

**** that diagram is gonna take me a week to understand

Jpr5690

iTrader: (13)

btw vss pulses are gonna be based on tire size and rear end gear so i guess that needs to be taken into consideration too

Jpr5690

iTrader: (13)

also why do you think it dosent work when grounded or unplugged? im guessing it realises its moving from the satalight and sees the discrepency so then it switches to satalight tracking of vehicle speed to disable the features

habeba86

iTrader: (2)

On a jvc unit we jst did the vss had to be hooked up or the unit will never calibrate and wont work

Jpr5690

iTrader: (13)

Ok New Idea,

Make A Relay That Is Connects The Ground When Activated And Source It From Either Your Hazard Flasher Or An Automotive Flasher That Is Added For This Reason,

Also Mabye I Can Find Some Sort Of 2 Pole Relay That Will Switch Between The 2 Modes (ie: No Signal= Vss Sensnsor Is Connected To Radio , Signal = Pulsing Ground)

Im Guessing I Will Need A Combo Of A Automotive Flasher, A Relay, And A 2 Pole Switch .. I Will Try And Diagram This Out Latter To Get My Thoguht Together..

As Of Now Just Cutting The Signal Will Buy You About 20 Secconds B4 The Raiod Figures It Out (which Aint Bad, But Id Like A Better Solution)

jimmyblue

iTrader: (11)

As long as the relay coil draws enough current for the
flasher to toggle (old-school ones need at least two
filaments, you'll see it get slow or not flash on turns
with a lamp out) that should work. Of course you'll
have to live with the click, click, click of the mechanicals.
Not sure how a solid-state flasher would work here. And
you're probably going to spend about the same money
either way.

Since you have 20 seconds, maybe just a SPST momentary
switch to ground and you get 20 seconds to dick with it,
want more, push the button again. Better than a bare wire
flapping around looking for sheet metal, anyway.

WhiteBird00

iTrader: (4)

I assume that this is all related to the "Pinout Diagram for 2007 Silverado" thread from a couple of days ago. I have been looking on some truck forums and the consensus seems to be that putting a simple on/off switch in the VSS line will work until the system loses satellite signal (overpass, tall buildings, or whatever) and tries to use the VSS signal to compensate. On open road you should be able to switch off the VSS signal, program your changes, and switch the signal back on without the nav unit even noticing.

Disclaimer: I have not tried this - it's just information posted by other GM truck owners. Your mileage may vary.

Jpr5690

iTrader: (13)

Just The Oppisite, The Vehicle Will Fault The Vss Signal As Soon As It Notices Its Not Present And The Satalight Says The Vehicle Is Moving..

If You Constantly Occilate The Signal At A Low Interval Then The Headunit Dosent Fault And I Guess Just Uses The Vss Ir Updates Every Now And Then To A New Position ( I Hadent Checked That Yet)

What I Do Know Is I Can Drive Arround For Like 10 Min With My Menus Unlocked So Long As Somebody Sits There And Taps The Vss Wire To A Ground Every Seccond Or So.. If You Let It Go For 10-20 Secconds With No Vss Signal It Seems To Ingore The Vss Signal There After Until You Shut Off The Car

Im Gonna Build This Little Device (this Week) And Ill Update To My Progress